Autodesk AliasStudio 2009
SDL: The Alias Scene
Description Language
March 2008
©
2008 Autodesk, Inc. All Rights Reserved. Except as otherwise permitted by Autodesk, Inc., this publication, or parts thereof, may not be
reproduced in any form, by any method, for any purpose.
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Published by:
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Contents
SDL: The Alias Scene Description Language . . . . . . . . . . . . 1
Chapter 1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
C Pre-Processor "#include" Statements . . . . . . . . . . . . . . . . . . . 7
The Rendering Pipeline . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Command Line Options . . . . . . . . . . . . . . . . . . . . . . . . . 11
Inserting comments in SDL . . . . . . . . . . . . . . . . . . . . . . . . 16
Scene Description Language Reference . . . . . . . . . . . . . 19
Designing SDL . . . . . . .
Notation . . . . . . . . . .
Layout . . . . . . . . . . .
New Keyword Equivalents
SDL File Roadmap . . . . .
Index of reserved words . .
Chapter 2
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. 19
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MODEL Section . . . . . . . . . . . . . . . . . . . . . . . . . . 37
assignment .
for . . . . . .
{}. . . . . . .
if . . . . . . .
instance . . .
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. 38
. 38
. 39
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iii
literal . . . . . . .
(null) . . . . . . . .
print . . . . . . . .
rotate . . . . . . .
translate . . . . . .
scale . . . . . . . .
translate_pivot . . .
translate_ripivot . .
translate_ropivot .
translate_sipivot . .
translate_sopivot .
Chapter 3
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. 42
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. 42
. 43
. 44
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. 45
. 45
. 46
. 46
. 47
DEFINITION Section . . . . . . . . . . . . . . . . . . . . . . . . 49
aalevelmax . . . . . . .
aalevelmin . . . . . . .
aathreshold . . . . . .
animation . . . . . . .
byextension . . . . . .
byframe . . . . . . . .
composite_rendering .
coverage_threshold . .
create . . . . . . . . .
endframe . . . . . . .
even . . . . . . . . . .
extensionsize . . . . .
fast_shading . . . . . .
fields . . . . . . . . . .
grid_cache . . . . . . .
hidden_line . . . . . .
hline_from_global . . .
hline_to_fill_color . . .
hline_fill_color . . . .
hline_line_color . . . .
hline_isoparam_U . . .
hline_isoparam_V . . .
ignore_filmgate . . . .
image_format . . . . .
matte . . . . . . . . .
max_reflections . . . .
max_refractions . . . .
max_shadow_level . .
motion_blur_on . . . .
odd . . . . . . . . . . .
odd_field_first . . . . .
output . . . . . . . . .
post_adjacent . . . . .
iv | Contents
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. 53
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. 56
. 57
. 57
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. 59
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. 61
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. 63
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. 65
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. 66
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. 70
. 71
. 72
. 73
. 74
. 74
. 75
. 76
. 77
post_center . . . . . . . . . . .
post_diagonal . . . . . . . . . .
post_filter . . . . . . . . . . . .
preview_ray_trace . . . . . . . .
quiet . . . . . . . . . . . . . . .
resolution . . . . . . . . . . . .
show_particles . . . . . . . . . .
shutter_angle . . . . . . . . . .
simulation_substeps . . . . . . .
simulation_frames_per_second .
small_features . . . . . . . . . .
startextension . . . . . . . . . .
startframe . . . . . . . . . . . .
stereo . . . . . . . . . . . . . .
stereo_eye_offset . . . . . . . . .
subdivision_control . . . . . . .
subdivision_recursion_limit . . .
textures_active . . . . . . . . . .
use_wavefront_depth . . . . . .
use_saved_geometry . . . . . . .
version . . . . . . . . . . . . . .
xleft . . . . . . . . . . . . . . .
xright . . . . . . . . . . . . . .
yhigh . . . . . . . . . . . . . .
ylow . . . . . . . . . . . . . . .
Chapter 4
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. 78
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. 83
. 84
. 84
. 85
. 86
. 87
. 87
. 89
. 90
. 91
. 92
. 93
. 93
. 94
. 95
. 96
ENVIRONMENT Section . . . . . . . . . . . . . . . . . . . . . . 99
background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
fog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
dynamics global parameters . . . . . . . . . . . . . . . . . . . . . . . 103
gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
air_density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
floor_offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
ceiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
ceiling_offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
left . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
left_offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
right . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
right_offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
front_offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
back . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
back_offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
wall_friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
wall_elasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Contents | v
turbulence_animated . . . .
turbulence_granularity . . . .
turbulence_intensity . . . . .
turbulence_persistence . . . .
turbulence_roughness . . . .
turbulence_space_resolution .
turbulence_spread . . . . . .
turbulence_time_resolution .
turbulence_variability . . . .
photo_effects . . . . . . . . .
auto_exposure . . . . . . . .
film_grain . . . . . . . . . .
filter . . . . . . . . . . . . .
master_light . . . . . . . . .
intensity . . . . . . . . . . .
light_color . . . . . . . . . .
shader_glow . . . . . . . . .
glow_color . . . . . . . . . .
glow_eccentricity . . . . . . .
glow_opacity . . . . . . . . .
glow_radial_noise . . . . . .
glow_star_level . . . . . . . .
glow_spread . . . . . . . . .
glow_type . . . . . . . . . .
halo_color . . . . . . . . . .
halo_eccentricity . . . . . . .
halo_lens_flare . . . . . . . .
halo_radial_noise . . . . . .
halo_spread . . . . . . . . .
halo_star_level . . . . . . . .
halo_type . . . . . . . . . .
quality . . . . . . . . . . . .
radial_noise_frequency . . .
star_points . . . . . . . . . .
threshold . . . . . . . . . . .
Chapter 5
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. 111
. 112
. 112
. 113
. 113
. 114
. 114
. 115
. 115
. 116
. 116
. 117
. 117
. 118
. 118
. 119
. 120
. 120
. 121
. 122
. 123
. 123
. 124
. 125
. 125
. 126
. 127
. 127
. 128
. 129
. 129
. 130
. 131
. 132
. 132
Data Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Creating Data Items . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Declaring Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Specifying Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Chapter 6
Data types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Array Data Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Camera Data Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Curve Data Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
vi | Contents
CV Data Type . . . . . . . .
Face Data Type . . . . . . . .
Filename Data Type . . . . .
Light Data Type . . . . . . .
Motion_curve Data Type . . .
Parameter_curve Data Type .
Parameter_vertex Data Type .
Patch Data Type . . . . . . .
Polyset Data Type . . . . . .
Scalar Data Type . . . . . . .
Shader Data Type . . . . . . .
Texture Data Type . . . . . .
Transformation Data Type . .
Trim boundary Data Type . .
Trim b-spline Data Type . . .
Trim curve vertex Data Type .
Trim edge Data Type . . . . .
Trim face Data Type . . . . .
Trim_vertex Data Type . . . .
Triple Data Type . . . . . . .
Chapter 7
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. 172
. 173
. 185
. 186
. 286
. 286
. 288
. 289
. 314
. 330
. 331
. 364
. 377
. 377
. 378
. 380
. 381
. 382
. 383
. 384
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. 387
. 389
. 392
. 394
. 397
Procedural Textures and Natural Phenomena . . . . . . . . . 407
Common Texture Parameters . . . . . . . . . .
Common Parametric (2D) Texture Parameters .
Solid and Environmental Texture Parameters . .
Textures . . . . . . . . . . . . . . . . . . . . .
About solid textures . . . . . . . . . . . . . . .
About environment maps . . . . . . . . . . . .
Chapter 9
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Scene Description Language Reference . . . . . . . . . . . . . 387
Using Data Items . . . . . .
System Defined Variables .
System Defined Constants .
Expressions . . . . . . . . .
Functions . . . . . . . . . .
Chapter 8
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. 408
. 409
. 411
. 412
. 449
. 471
Tutorials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
Creating Rendered Cubic Environment Maps .
Creating projectile movement . . . . . . . . .
Programming Movement with Constraints . .
An Introduction to Dynamics . . . . . . . . .
Creating Fiery Smoke . . . . . . . . . . . . .
Animating a Sunrise . . . . . . . . . . . . . .
Creating a Tree . . . . . . . . . . . . . . . . .
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. 487
. 495
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. 515
Contents | vii
Creating Rendered Stereo Pairs . . . . . . . . . . . . . . . . . . . . . 519
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523
viii | Contents
SDL:The Alias Scene
Description Language
1
2
Introduction
1
SDL is the Scene Description Language. SDL programs, in the form of ASCII text files, specify
all the information necessary to render a scene, including models, shaders, lights, and
animation.
Because they are simple text files, SDL programs can be created “by hand”. That is, it is possible
to create a scene entirely using SDL commands. Usually, however, you will not need to directly
edit SDL files. Instead, they will be generated by an interactive modeling program. In fact,
most people will never need to read an SDL file, and will simply output SDL from the modeler
directly to the renderer automatically.
There are some cases where you may want to use SDL:
■
for absolute, mathematical control over scene elements such as models, animation paths,
and shaders
■
to modify a generated SDL file manually, or with another program
■
to create new procedural effects using the general programming features of SDL
Applying basic programming constructs to scene descriptions allows useful and spectacular
effects that would be tedious or impossible to create with the interactive modeler alone. SDL
can augment the dynamics and particle systems of the interactive modeler with the flexibility
of a programming language.
Once you have an SDL file describing a scene, you will run it through a renderer to create an
image of the scene.
Renderers
The renderers take an SDL file and create an image or images, as if it built the world described
in the SDL file and then photographed it. AliasStudio supports two methods of converting
the procedural information of the SDL file into an image: RayCasting and RayTracing.
3
RayCasting
The RayCaster follows a line (ray) for each pixel on the screen, from the camera eye into
the scene. As the rays meet objects in the scene, the RayCaster calculates the light reflected
off the object at that point. In effect the RayCaster work backwards from the real world, by
tracing light hitting the eye back to the object that reflected it.
How It Works
This illustration shows how the raycaster works:
■
Ray 1 doesn’t hit any object, and so hits the background. The RayCaster assigns the
background color (or picture) to the pixel where the rays passed through the screen.
■
Rays 2,4, and 5 hit opaque objects in the scene. The RayCaster calculates the color of
the objects where the rays hit them. It then takes into account lights, shaders, and special
effects (such as fog). Then it assigns that color to the pixel where the rays passed through
the screen.
■
Ray 3 passes through a translucent glass cup before hitting the tabletop. The RayCaster
calculates the color of the tabletop at that point, just as for rays 2,4, and 5. Then it adds
the amount of color the ray received from passing through the glass cup. Finally it assigns
that color to the pixel where the ray passed through the screen.
4 | Chapter 1 Introduction
At each intersection between a ray and an object, the RayCaster combines the surface
geometry, the lights in the scene, and the surface shading model to calculate the color for
that spot. The shading model is a mathematical expression of the way the surface interacts
with light. It is controlled by several parameters, such as surface color and shinyness, that
can be constant over the surface (for solid colors), vary with U and V (for 2D textures), vary
with XYZ (for solid textures), or vary with time (for animated colors and textures).
After calculating the color of the surface hit, the RayCaster takes into account atmospheric
effects. That is, the medium through which the rays travel (for example, fog or water). These
effects are controlled in the ENVIRONMENT section of SDL.
Once the RayCaster has completely processed a ray, taking into account surfaces and
atmospheric effects, it has an RGB color value for the corresponding pixel on the screen.
Depending on the options set when the RayCaster was run, it will use assign this color to
the pixel, or calculate many rays per pixel and average their colors together for a
“representative” color. This averaging is called anti-aliasing, and it helps to smooth out the
blocky look of computer graphics. The amount of anti-aliasing is controlled in the
DEFINITION section of SDL.
RayTracing
RayTracing is similar to RayCasting in many ways, but has one important difference — the
ray of light doesn’t necessarily stop when it hits an opaque object. It can bounce off to
another object and another and another, retracing and reflecting everything it sees in the
scene. The AliasStudio RayTracer follows as many bounces as you want.
RayTracing is more time-consuming than RayCasting, and for most scenes is not worth the
extra time. However, it gives you the most realistic image possible. Because the ray is traced
through multiple bounces, the RayTracer is able to produce effects the RayCaster cannot:
■
true reflections from reflective surfaces (to save rendering time, AliasStudio lets you
choose which objects in a scene will have reflections)
■
true refraction through transparent surfaces
■
true shadows from multiple light sources
■
shadows cast through transparent objects
How It Works
The RayTracer follows the path of rays from the camera eye into the scene. Rays originating
at the camera are the primary rays. As the primary rays intersect objects, they may reflect
or refract according to simplified optical physics, and produce secondary rays. The secondary
rays are followed in the same manner, and so on.
|5
Each time a ray intersects an object, the RayTracer traces shadow rays from that point toward
each lights set to cast shadows. If the shadow ray meets another surface before reaching the
light, the point is shaded from the light.
The following illustration shows what would happen to ray 3 of the RayCasting example
above, if it were rendered with RayTracing.
The ray (a) travels from the eye to the glass cup. Where it contacts the shiny translucent
glass, it splits into secondary rays (b) and (d). One secondary ray (b) refracts through the
glass a different angle (according to the material of the glass cup). The other secondary ray
(d) reflects off the glass and hits the tabletop. The refracted ray (b) hits the other side of the
glass and refracts again (c), hitting the tabletop at a different place.
The RayTracer processes all this information and calculates a color for the pixel where the
ray passed through the screen. To save rendering time, the RayTracer lets you limit the
number of bounces or secondary rays it will generate from an intersection with a surface.
PowerCaster and PowerTracer
PowerCaster and PowerTracer are multiprocessor versions of the RayCaster and RayTracer.
6 | Chapter 1 Introduction
C Pre-Processor "#include" Statements
Even a basic scene composed of cubes — each of which is represented by six
patches — can look very imposing when printed out in a single SDL file.
To reduce the bulk of SDL files, you can use “#include” statements in the main
SDL file and break the monolithic scene description into smaller, more
manageable pieces. Before rendering, you use the C Pre-Processor to replace
the “#include” statements with the smaller auxiliary files.
This method has several benefits when working with large SDL files by hand:
■
allows you to isolate and separately maintain different types of scene
description (for example, CV lists in one file, lights in another file, shaders
in another file)
■
makes it easier to edit files (smaller files load and display faster in an editor)
■
allows you to replace redundant geometry (for example, two identical
objects in a scene) with #include statements referencing the same file,
while the different transformations for the objects remain in the main SDL
file
Setting Up Include Files
Before beginning to create include files, consider creating a directory called
include in the sdl directory. Putting SDL include files there reduces clutter
and confusion.
To move parts of a master SDL file into smaller include files:
1 Copy the SDL text you want to include into a new file.
2 Candidates for replacement are long CV lists, lights, shaders, repetitive
or complex geometry and transformations, and animation definitions.
3 Give a meaningful name to the new file containing the text to be
included.
4 By convention, include files end with “.h”, but you can give them any
name you want.
5 In the master SDL file, replace the text you just copied with a line
beginning with #include, followed by a space and the quoted path to the
file to be included. For example: #include “/h/frank/includes/geom.h”
C Pre-Processor "#include" Statements | 7
6 Repeat for each section of SDL text you want to move into an include
file.
Recreating the SDL File for Rendering
Before you can render SDL files with #include statements, you must expand
them by replacing the #include statements in the master SDL file with the
text contained in the corresponding include files. To do this, you will run the
master SDL file through the C Pre-Processor, cpp.
NOTE The AliasStudio interactive software and the renderit script both run cpp
on SDL files automatically.
To manually expand an SDL file for rendering:
1 At a shell prompt, type
2 /lib/cpp -C -P sdl/masterSDLfile temp
3 Where masterSDLfile is the name of the SDL file with the include
statements. This runs the master SDL file through cpp and creates a new
file called temp, which is the result of replacing the “#include” statements.
4 At the prompt, type
5 renderer temp
6 This runs the renderer on the recreated file.
The Rendering Pipeline
In the pre-processing phase, the RayCaster:
1 Takes face, patch, and polygon statements from the SDL file.
2 Transforms the control vertices of each object according to the SDL
hierarchy of transformations.
3 Converts the geometry into triangles.
4 The number of triangles depends on the tessellation control settings. The
vertex of each triangle stores surface U and V parameters, tangent vectors,
surface normal, and position in world space.
8 | Chapter 1 Introduction
5 Applies the perspective viewing transformation, which includes the
camera location, viewpoint, field of view, and twist.
6 This step converts the triangles from world space to perspective (screen)
space.
7 The triangles are “scanned out” to the triangle buffer (each pixel inside
the two-dimensional boundary of the screen space triangle is identified).
In the rendering phase, the RayCaster loops through each pixel of the new
image and calculates:
1 The light reflected toward the camera by each surface.
2 U and V parameter values, tangent vectors, surface normal, and position
for each intersection point with a triangle (calculated by interpolating
from the information on the intersected triangle in the triangle buffer).
3 Color and transparency values for the intersected triangle(s) based on
the geometry of the intersecting point, the lights in the scene, and the
surface shading model.
4 Final color (RGB) and transparency (alpha) of the pixel based on the
colors and transparencies of the intersected triangle(s).
The final step of combining all the intersected triangles into a final color is
complex.
If the ray intersects more than one triangle, the list of intersections is sorted
by distance from the camera and processed from back to front. The renderer
builds the final color and transparency by combining the colors and
transparencies of each triangle, along with the atmospheric effects between
the triangles. See the Procedural Textures and Natural Phenomena on page
407section of the SDL Reference Manual for more information on how these
colors are calculated and combined.
This illustration shows the complex process by which the renderer combines
the colors of the intersected triangles. It does not show the additional
complexities introduced by motion blur.
The Rendering Pipeline | 9
10 | Chapter 1 Introduction
The following illustration shows an example of how both the surfaces and
ray segments are used to calculate the color and transparency of a pixel.
To calculate the ray illustrated above, the renderer starts with the color and
transparency of the background. Then it calculates the atmospheric effects of
the rightmost ray segment (the segment between the farthest surface and the
background) and adds them to the color and transparency of the background.
Then it adds the color and transparency of the farthest surface, then the next
closest, and so on. Note that if any of the surfaces are opaque (transparency
0), the color information of farther surfaces is lost, since the opaque surface
completely obscures the surfaces behind it.
Command Line Options
Any options you give the renderer on the command line override internal
variables in the SDL file. These options allow you to change the behavior of
the renderer without having to edit the SDL file.
Usage
To use the command line options
1 Use the cd command to move to your project directory (for example, cd
user_data/demo).
2 Enter the command for the renderer, followed by any options (see below),
and the name of the SDL file (for example, renderer -s10 sdl/animation_1).
Command Line Options | 11
Options
renderer|raytracer [-H] [-an]
[-bn] [-en] [-f script] [gn][-hn] [-m filename] [-p
filename] [-d filename] [-C
color_map_filename] [-c
quantized_output_file] [-j]
[-k] [-Kn] [-on] [-O][-qn][P][-sn] [-Sn] [-Bn] [-En] [rn] [-tn] [-wn] [-Wn] [-xn]
[-yn] [-Yn] [-zn] [-Zn] [file
name]
-an
Use the integer n as the aalevel.
-tn
Use the integer n as the aathreshold.
-sn
Use the float n as the starting frame number.
-bn
Use the float n as the by frame number.
-en
Use the float n as the ending frame number.
-Sn
Use the integer n as the start extension.
-Bn
Use the integer n as the by extension.
-En
Use the integer n as the size extension.
-fstring
invoke the program string after each frame.
-gn
Use the float n as the gamma correction
value.
12 | Chapter 1 Introduction
-mstring
Produce a matte file and Use string as the
filename.
-pstring
Use string as the pix filename.
-dstring
Use string as the depth file name.
-C string
Use the SGI imagelib image format file to
quantize to after each frame.
-c string
Output the quantized image to the file
string after each frame.
-j
Raytrace transparent objects without attenuation (Beere’s law ignored).
-k
Keep depth maps in memory after reading
(read them once).If used, a depth map file
will be read ONCE, or if depth map saving
is not turned on, the map will be created
ONCE and used for all subsequent frames.
-Kn
Turn depth maps on disk usage to n. 0=off,
non-zero =on.If used, a depth map file
named the same as the light will be created
if it doesn’t exist, and used if it does exist.
-O
Use byframe of 1.0 as applied to motionblur.
-on
Use byframe of n as applied to motionblur.
-P
Preserve the non-glowed image.
-qn
Set the quiet flag to n (0 or 1).
Command Line Options | 13
-Tn
Use the integer n as the number of Y pixels
in a tile.
-hn
Use the integer n as the image height.
-wn
Use the integer n as the image width.
-Wn
Use the integer n as the ylow for backgrounds.
-xn
Use the integer n as the xleft.
-yn
Use the integer n as the ylow.
-Yn
Use the integer n as the yhigh for backgrounds.
-rn
Use the float n as the aspect ratio.If more
than one camera is defined in the SDL file,
this option only affects the first camera.
-Gn
Turn saved geometry on (non-zero n) or
off (0).
filename
Use filename as the SDL filename. If no filename is present standard input will be
used.
-zn
Make camera depth output respect transparency, if transparency is greater or equal
to n.This allows transparency mapped objects to affect the camera depth output
files. If the flag is set to 1, anything that is
at least 1% transparent will not show up
in the depth file. If the flag is set to 50,
anything that is more than 50% transparent will not show up in the depth file. If it
is set to 99, only things that are totally
14 | Chapter 1 Introduction
transparent will not show up in the camera
depth file.
-Zn
Set fast_shading to n (0 or 1).
-H
Print a usage message.
PowerCaster and PowerTracer Options
The multi-processor renderers have a few extra options for controlling how
they use multiple CPUs.]
powertracer|powercaster [-H] [-an] [-bn]
[-en] [-f script] [-gn][-hn] [-m filename] [p filename] [-d filename] [-C color_map_filename] [-c quantized_output_file] [-qn] [sn] [-Sn] [-Bn] [-En] [-rn] [-Wn] [-Yn] [-k] [Kn] [-on] [-O] [-P][-tn] [-wn] [-xn] [-yn] [nn] [-I] [-Tn] [-U] [-zn] [-Zn] [filename]
-nn
Use the integer n as the number of processors to PowerTrace on.
-I
Print out statistics at the end of the
PowerTrace.
-Tn
Use the integer n as the number of Y pixels
in a tile.
-U
Leave output pix file uncompressed (not
Run Length Encoded).
All other options are identical to the single
processor commands.
Command Line Options | 15
Examples
Example 1
To render every other frame (“by frame” of 2) of frames 4 through 8 of an
animation, but number the output files 10,11 and 12, enter:
renderer -s 4 -e 8 -b 2 -S 10 -B 1 sdl/animation_scene_1
This produces the following pix files:
pix/animation_scene1.10 (which is frame 4)
pix/animation_scene1.11 (which is frame 6)
pix/animation_scene1.12 (which is frame 8)
Example 2
To test a few frames of an animation (say, frames 1 to 5) without overwriting
existing pix files, enter:
renderer -e 5 -p pix/test_anim -m mask/test_anim sdl/anima
tion_scene_1
This produces the following pix and mask files:
pix/test_anim.1
pix/test_anim.2
pix/test_anim.3
pix/test_anim.4
pix/test_anim.5
mask/test_anim.1
mask/test_anim.2
mask/test_anim.3
mask/test_anim.4
mask/test_anim.5
Inserting comments in SDL
To insert comments in an SDL file, enclose the line or lines with a “C style”
slash-asterisk pair:
/* comment */
or
16 | Chapter 1 Introduction
/*
comment
comment
comment
*/
You cannot nest comments.
NOTE The numeric sign (#) followed by a blank space is not a comment.
Inserting comments in SDL | 17
18
Scene Description
Language Reference
Designing SDL
The Scene Description Language is intended to describe a scene. It is not meant
for interaction. When Autodesk created SDL, the most important consideration
was its ability to clearly and succinctly describe a scene. This includes sufficient
scope to describe all aspects of a scene.
In addition, SDL had to be
■
practical in normal and extraordinary usage;
■
extensible to evolve as new features are added in the future;
■
flexible to cope with the differing needs of ID and video animation;
■
intuitive for first time and casual users;
■
rich with options for skilled and demanding users;
■
internally consistent for ease of teaching and documentation;
■
and consistent with the interactive package to avoid confusion.
The above considerations argued for a language rich in nouns and adjectives,
with fewer verbs. In terms of computer language design, that means many data
types with many optional modifiers and relatively few operations. The bulk of
this document, therefore, deals with data.
19
Notation
We have tried to keep the vocabulary in this document strictly defined. For
example, each data type has a unique name. That name is not used with any
other meaning in this document.
This document does not include a glossary, since any description of the terms
used would simply repeat the description of the language feature. Please check
the table of contents for any term which is unfamiliar, since most terms
important to SDL have their own section.
Three-dimensional coordinates and directions are specified using the x,y,z
system, corresponding to the system used by the modeler.
Reserved words are printed in bold.
Layout
There are five sections in this part of the manual:
■
SDL File Roadmap on page 20
■
Using Data Items
■
System Defined Variables on page 389 and System Defined Constants on
page 392
■
Expressions on page 394 and Functions on page 397
New Keyword Equivalents
Starting with version 7, some keywords have shorter “nicknames”, allowing
smaller file sizes and easier typing. For example you can now use cl instead
of cluster, inst instead of instance, pc instead of parameter_curve, and so on.
SDL File Roadmap
This is a roadmap of an SDL file. Every item that can be included is shown
here, but if your model does not use any of these features they should not
appear in the SDL file.
20 | Part 1 Scene Description Language Reference
An SDL file is divided into three sections: DEFINITION, ENVIRONMENT, and
MODEL. The sections are preceded by section titles, which are entered on a
line in all caps with no punctuation.
The camera is listed last in this example layout, but it may appear anywhere
in the MODEL section, and there can be more than one camera. Note that
the camera object contains the mask, depth_file, and pix file name
specifications.
DEFINITION Section
■
system variables (for example, aalevel, frame range, ray tracing levels)
■
animation curves (motion paths and timing curves)
■
camera view variable(s)
■
light definitions
■
shader and texture definitions
■
trim curve definitions
■
patch and face definitions (note: text is now represented as faces)
ENVIRONMENT Section
■
background type (file, ramp, color, procedural, none)
■
fog specification
MODEL Section
■
instances and transformations (the building blocks of a model)
■
camera(s) (contains output image file name)
Index of reserved words
Reserved word
Type
aawidth
keyword
abs_bump
keyword
Index of reserved words | 21
Reserved word
Type
abs_disp
keyword
acos
Scalar Function
acosd
Scalar Function
active
keyword
ambient_shade
keyword
animate
Function
animation
keyword
array
keyword
asin
Function
asind
Function
aspect
keyword
atan
Function
atan2"
Function
atan2d
Function
atand
Function
AVERAGE_TAN
keyword
B
background
keyword
22 | Part 1 Scene Description Language Reference
Reserved word
Type
besselj0
Function
besselj1
Function
besseljn
Function
bessely0
Function
bessely1
Function
besselyn
Function
biasmax
keyword
biasmin
keyword
BLEND_TAN
keyword
boundaries
keyword
bump
keyword
by_extension
keyword
C
camera
keyword
casts_shadow
keyword
ceil
Function
cl
CV Function
cluster
CV Function
Index of reserved words | 23
Reserved word
Type
clusters
keyword
clm
keyword
cluster_matrix
keyword
color
keyword
color_table
keyword
colour
keyword
colour_table
keyword
CONSTANT_TAN
keyword
cos
Function
cosd
Function
cosh
Function
create
keyword
current_position
Function
current_transformation
Function
cur_xform
Transform function
Curvature
keyword
curvature
keyword
curve
keyword
24 | Part 1 Scene Description Language Reference
Reserved word
Type
cv
keyword
cvs
keyword
D
decay
keyword
DEFINITION
Header
degree
keyword
depth_input
keyword
depth_file
keyword
depth_of_field
keyword
depth_output
keyword
diffuse
keyword
direction
keyword
displacement
keyword
divisions
keyword
doublesided
keyword
drop_size
keyword
dropoff
keyword
E
Index of reserved words | 25
Reserved word
Type
ease
keyword
eccentricity
keyword
else
keyword
end
keyword
ENVIRONMENT
ENVIRONMENT Header
environment
keyword
erf
Function
erfc
Function
even
keyword
execute_edl
keyword
exp
Function
EXPIN
Ease type
EXPOUT
Ease type
extension_size
keyword
eye
keyword
F
f_stop
keyword
fabs
Function
26 | Part 1 Scene Description Language Reference
Reserved word
Type
face
keyword
far
keyword
fast_shading
keyword
fields
keyword
filename
keyword
floor
Function
fmod
Function
focal_distance
keyword
focal_length
keyword
fog
keyword
for
keyword
fov
keyword
frame_rate
keyword
G
gamma
Function
gauss
Function
grid_cache
keyword
H
Index of reserved words | 27
Reserved word
Type
Highlight
keyword
hypot
Function
I
if
keyword
IN
Ease type
incandescence
keyword
INOUT
Ease type
INOUT_TAN
keyword
inst
keyword
instance
keyword
intensity
keyword
J
jitter
keyword
JOINT
Cluster type
K
knots
keyword
L
LEAF
Cluster type
28 | Part 1 Scene Description Language Reference
Reserved word
Type
light
keyword
light_list
keyword
LINEAR
Ease type
LINEAR_TAN
keyword
lo_res
keyword
log
Function
log10
Function
M
mask
keyword
mate_curve
keyword
mate_patch
keyword
mate_type
keyword
matte
keyword
max_reflections
keyword
max_refractions
keyword
max_shadow_level
keyword
mode
keyword
MODEL
MODEL Header
Index of reserved words | 29
Reserved word
Type
model
keyword
motion
Function
N
name
keyword
near
keyword
O
odd
keyword
opposite
keyword
optical_medium
keyword
OUT
Ease Type
output
keyword
P
parameter_curve
keyword
parameter_vertex
keyword
patch
keyword
pc
keyword
pix
keyword
position
keyword
30 | Part 1 Scene Description Language Reference
Reserved word
Type
pow
Function
preview_ray_trace
keyword
print
keyword
procedure
keyword
pv
keyword
Q
quiet
keyword
R
ramp
keyword
rand
Function
raycast
Mode Type
record_device_number
keyword
reflection
keyword
reflection_limit
keyword
reflectivity
keyword
refraction_limit
keyword
refractive_index
keyword
resolution
keyword
Index of reserved words | 31
Reserved word
Type
respect_reflection_map
keyword
rot
keyword
rotate
keyword
S
scalar
keyword
scale
keyword
sclr
keyword
shader
keyword
shadow
keyword
shadow_level_limit
keyword
shadow_output
keyword
shadow_volume
keyword
shadowmult
keyword
shadowoffset
keyword
shared_edge
keyword
shine_along
keyword
shinyness
keyword
sign
Function
32 | Part 1 Scene Description Language Reference
Reserved word
Type
sin
Function
sind
Function
sinh
Function
size
keyword
SLOWIN_TAN
keyword
SLOWOUT_TAN
keyword
smallfeatures
keyword
space
keyword
specular
keyword
spread
keyword
sqrt
Function
srand
Function
start
keyword
start_extension
keyword
stereo
keyword
stereo_eye_offset
keyword
subdivide
keyword
subdivision_control
keyword
Index of reserved words | 33
Reserved word
Type
subdivision_recursion_limit
keyword
T
tan
Function
tand
Function
tanh
Function
tb
keyword
tbs
keyword
tcv
keyword
te
keyword
texture
keyword
tf
keyword
time_code
keyword
transformation
keyword
translate
keyword
transparency
keyword
transparency_shade
keyword
trim_curve
keyword
trim_hole
keyword
34 | Part 1 Scene Description Language Reference
Reserved word
Type
trim_region
keyword
trim_vertex
keyword
triple
keyword
trn
keyword
trn_ro
keyword
trn_ri
keyword
trn_so
keyword
trn_si
keyword
twist
keyword
type
keyword
U
uclosed
keyword
udegree
keyword
uknots
keyword
units_to_feet
keyword
up
keyword
use_saved_geometry
keyword
V
Index of reserved words | 35
Reserved word
Type
value
keyword
vclosed
keyword
vdegree
keyword
version
keyword
view
keyword
viewport
keyword
vknots
keyword
W
warp
Function
wireframe
Mode
X
xaxis
Axis Type
xform
keyword
Y
yaxis
Axis Type
Z
zaxis
Axis Type
ZERO_TAN
keyword
36 | Part 1 Scene Description Language Reference
MODEL Section
2
The MODEL section describes the instances of the objects that were defined in the DEFINITION
section, along with information for position, orientation, relationships between objects, and
behavior over time. The MODEL section contains statements about data items (for creating,
inspecting, and transforming), and control statements (for conditional execution and looping).
NOTE The MODEL section is similar to the old GEOMETRY section, but uses objects
defined in the DEFINITION section.
The MODEL section begins with the word MODEL in all caps on a separate line with no
punctuation. The section ends when the SDL file ends.
The following statements are described in this section:
■
<assignment on page 38>
■
for on page 38
■
if on page 40
■
instance on page 41
■
<literal on page 42>
■
print on page 42
■
rotate on page 43
■
scale on page 44
■
<(null) on page 42>
■
translate on page 44
■
translate_pivot on page 45
■
translate_ripivot on page 45
■
translate_ropivot on page 46
■
translate_sipivot on page 46
37
■
translate_sopivot on page 47
■
{ } on page 39
assignment
Syntax:
<left hand side> = <right hand side> ;
Purpose:
This assigns the value of the item on the right to the item on the left. The
item on the right is not modified or otherwise effected in any way. The <left
hand side> may be a variable name, an array name, or an array element
reference. The <right hand side> may be a literal, a variable reference, an array
name, or an array ele-ment reference or a function. However, only certain of
the possible combinations are valid. The following rules de-termine the validity.
If the <left hand side> is an array element reference, then any of the <right
hand side> possibilities may be used.
If the <left hand side> is a variable name, the <right hand side> may be a
literal, a variable reference, or an array element reference or a function,
provided that the data types of the <left hand side> and the <right hand side>
are the same.
Example:
switch = FALSE;
bunch[1] = some_var;
for
Syntax:
for ( <initial statement>; <condition> ; <iteration statement>; ) <body
statement>
38 | Chapter 2 MODEL Section
Purpose:
The for statement provides a means of iterating loops of statements. The
struc-ture of the for statement is considerably more powerful than that
provided by most lan-guages. The particulars of it are different than “C”, but
have a similar flavor.
The <initial statement> is any statement valid in the MODEL section. Typically
it will be an assignment, but it is not limited to that. (It could be a (null) on
page 42 grouping or even a nested for statement.) An <initial statement> must
be specified.
The <condition> is just an expression interpreted as a truth value. An
expression is considered true if its value is non-zero, and false if its value is
zero. If <condition> is true, then the <body statement> will be executed. If
<condition> is false, then control immediately passes to the statement
following the for state-ment. A <condition> must be specified.
The <iteration statement> is any statement valid in the MODEL section. An
<iteration statement> must be specified. The <body statement> is any statement
valid in the MODEL section. A <body statement> must be specified.
All the elements of a for statement are always required. The parentheses and
semi-colon are part of the syntax, and required. The end of a for statement is
marked by the end of the <body statement>.
There are four parts to the execution of a for statement. First, the <initial
state-ment> is executed. Second, the <condition> is tested. The result of this
is either continued execution or the end of the for statement. Third, if
execution is to be continued, the <body statement> is executed. Fourth, the
<iteration statement> is executed. Following this, control reverts to the second
step, testing the <condition>, and pro-ceeds from that point. Execution
continues in this way until the <condition> evalu-ates to false.
Example:
for ( x=0; x < 10; x = x+1;) print("digit =", x );
{}
Syntax:
{ <statement> <statement> … <statement> }
{ } | 39
Purpose:
An arbitrary number of MODEL section statements may be grouped together
through the use of the brace bracket characters, { and }. The start of the group
is marked by the opening brace, {. The end of the group is marked by the
closing brace, }. All statements between the braces are treated as though they
were one single statement. Transformation statements (rotate on page 43,
translate on page 44 and scale on page 44) only have effect within the group.
Instances and literals create objects in the scene. Assignments effect the value
of variables, which retain their values across the boundaries of the group. All
other statements behave in their normal manner. Groups may be nested to
any degree.
Groups are useful for two purposes. First, groups allow hierarchies of objects
and transformations to be constructed. When used in this sense, they are
identical to the groups found in the interactive package. Second, groups are
useful for ex-tending the range of effect of if statements and for statements.
This usage of groups is not presently available in the interactive package. It
is, however, vary similar to syntactic constructs in “C” and other programming
languages.
if
Syntax:
if ( <condition> ) <true statement> else <false statement>
or
if ( <condition> ) <true statement>
Purpose:
The if statement is used to conditionally execute statements. The <condition>
is just an expression interpreted as a truth value. An expression is considered
true if its value is non-zero, and false if its value is zero. If <condition> is true,
the <true state-ment> is executed. Otherwise, the <false statement> is executed.
The if statement can be abbreviated by omitting the else and the <false
statement>.
In its abbreviated form, the if statement will execute the <true statement> if
the <condition> is true, and pass on to the next statement if it is false. <true
state-ment> and <false statement> may be any statement valid in the MODEL
section (including if statements and {} groupings). The end of an if statement
40 | Chapter 2 MODEL Section
is marked by the end of the <false statement> (or by the end of the <true
statement> in the abbreviated form).
Example:
if (frame > 1)
begun = TRUE;
instance
Syntax:
instance <object reference> ();
or
inst <object reference> ();
Purpose:
The instance statement creates an instance of an object. The <object reference>
may be either a variable reference or an array element reference. In either case,
an object is created from the data item. The data item being referenced must
be of an appropriate type (that is, Light Data Type on page 186, Patch Data
Type on page 289, Face Data Type on page 173, or Camera Data Type on page
140). If the <object reference> is a variable ref-erence, then the type check is
performed at parse time, otherwise it is performed at instancing time. If an
improper data type is given, a warning message is issued and execution
continues with the instance ignored. The effect of an instance is the same as
if a literal of the same type and having the compo-nent values of the <object
refer-ence> were used instead.
The end of an instance statement is marked by a semi-colon.
Note that inst and instance keywords can be used interchangeably.
Example:
instance sphere_patch();
instance | 41
literal
Syntax:
The syntax of a literal definition varies, depending upon the data type of the
lit-eral being defined. The reader is referred to the detailed description of the
data types for the exact syntax of each. Note that only literals of “objects”
may be used. That is, only Light Data Type on page 186, Patch Data Type on
page 289, Face Data Type on page 173, and Camera Data Type on page 140 are
valid. If an improper data type is given, a warning is issued and execution
continues with the literal ignored.
Purpose:
The specification of a literal object places that object in the scene at the
location and with the size and orientation determined by the current transform
matrix. The end of a literal statement is marked by a semi-colon.
(null)
Syntax:
;
Purpose:
The null statement (a lone semi-colon) is a valid and well-defined statement
that does nothing. It is useful in those situations where a statement is required,
but no action is desired. For example, a for statement with an empty initial
statement could be writ-ten as
for ( ; x < 5; x = x+1; ) print("count =", x );
print
Syntax:
print ( "string", <scalar | triple> ) ;
or
42 | Chapter 2 MODEL Section
print ( "string" ) ;
Purpose:
This statement prints a string and the value of a scalar, or just a string. The
string is required, although it may be empty.
print may be used by itself, for example
print ("This just prints a comment");
Alternately, print may be used as a function within some larger construct.
When used in this way, print passes the value of the variable through as though
the print were not there at all. For example,
x = print ("x = ", a );
results in x being assigned the value of variable a. If only a string is given (no
vari-able), the passed through value is scalar(0). Thus,
x = print ("This is just a comment");
is equivalent to assigning the scalar value 0 to variable x. The end of a print
statement is marked by a semicolon.
If the item being printed is a triple, the return value of the print statement is
also a triple.
Example:
print("a thing", thing);
rotate
Syntax:
rotate ( <axis index>, <scalar> ) ;
or
rot ( <axis index>, <scalar> ) ;
Purpose:
Rotations are performed about an axis. The <axis index> specifies which axis
to ro-tate about. The <axis index> is just a scalar, interpreted as an integer. It
must have a value of 0, 1 or 2, where a value of 0 indicates rotation about the
rotate | 43
x axis, 1 indicates rotation about the y axis, and 2 indicates rotation about
the z axis. Three system de-fined constants are provided (xaxis on page 393,
yaxis on page 393, and zaxis on page 394) for convenience in specifying the
<axis index>. The <scalar> specifies the amount of rotation (measured in
de-grees). The order of application for rotate statements is impor-tant. A rotate
statement for the x axis followed by one for the z axis does not have the same
effect as the re-verse order of application. The end of a rotate statement is
marked by a semi-colon.
Note that rot and rotate keywords can be used interchangeably.
Example:
rotate(zaxis, 45);
translate
Syntax:
translate <triple> ;
or
trn <triple> ;
Purpose:
The <triple> indicates the direction in which the subsequent geometry is
moved. The end of a translate statement is marked by a semi-colon.
Note that trn and translate keywords can be used interchangeably.
Example:
translate (0,15,0.2);
scale
Syntax:
scale <triple> ;
44 | Chapter 2 MODEL Section
Purpose:
The components of the <triple> multiply the coordinate values of points for
each of the x, y and z directions with respect to the origin. A scale of (1,1,1)
has no ef-fect on the objects, while a scale of (1, 1, 1.5) creates a 50 percent
increase in the z dimension. Note that a scale of (0, 0, 0) is an error; it is ignored
by the renderer, and a warning message is given. The end of a scale statement
is marked by a semi-colon.
Example:
scale (1,1,0.2);
translate_pivot
Syntax:
translate_pivot <triple>;
Purpose:
The <triple> indicates the direction in which the subsequent geometry is
moved. The end of a translate_pivot statement is marked by a semi-colon.
translate_pivot is similar to translate on page 44, except translations used in
translate_pivot do not get used in cluster matrix building.
Example:
translate_pivot (0.1, 3.0, 2.5);
translate_ripivot
Syntax:
translate_ripivot <triple>;
or
trn_ri <triple>;
translate_pivot | 45
Purpose:
The <triple> indicates the direction in which the subsequent geometry is
moved. The end of a translate_ripivot statement is marked by a semi-colon.
translate_ripivot is similar to translate on page 44, except translations used
in translate_ripivot do not get used in cluster matrix building and only affects
rotation in.
Note that trn_ri and translate_ripivot can be used interchangeably.
Example:
translate_ripivot (0.1, 3.0, 2.5);
translate_ropivot
Syntax:
translate_ropivot <triple>;
or
trn_ro <triple>;
Purpose:
The <triple> indicates the direction in which the subsequent geometry is
moved. The end of a translate_ropivot statement is marked by a semi-colon.
translate_ropivot is similar to translate on page 44, except translations used
in translate_ropivot do not get used in cluster matrix building and only affects
rotation out.
Note that trn_ri and translate_ripivot can be used interchangeably.
Example:
translate_ropivot (0.1, 3.0, 2.5);
translate_sipivot
Syntax:
translate_sipivot <triple>;
46 | Chapter 2 MODEL Section
or
trn_si <triple>;
Purpose:
The <triple> indicates the direction in which the subsequent geometry is
moved. The end of a translate_sipivot statement is marked by a semi-colon.
translate_sipivot is similar to scale on page 44, except translations used in
translate_sipivot do not get used in cluster matrix building and only affects
scale in.
Note that trn_si and translate_sipivot can be used interchangeably.
Example:
translate_sipivot (0.1, 3.0, 2.5);
translate_sopivot
Syntax:
translate_sopivot <triple>;
or
trn_so <triple>;
Purpose:
The <triple> indicates the direction in which the subsequent geometry is
moved. The end of a translate_sopivot statement is marked by a semi-colon.
translate_sopivot is similar to scale on page 44, except translations used in
translate_sopivot do not get used in cluster matrix building and only affects
rotation out.
Note that trn_si and translate_sipivot can be used interchangeably.
Example:
translate_sopivot (0.1, 3.0, 2.5);
translate_sopivot | 47
48
DEFINITION Section
3
The DEFINITION section contains definitions of all the entities that will be “instanced” later
in the MODEL section, similar to declaring variables before using them in traditional
programming languages.
The DEFINITION section is the place for definitions of:
■
system variables (for example, aalevel, frame range, ray tracing levels)
■
animation curves (motion paths and timing curves)
■
camera view(s)
■
lights
■
shaders and textures
■
trim curves
■
patches and faces
NOTE The background and atmospheric effects are defined in the ENVIRONMENT section.
The DEFINITION section begins with the word DEFINITION in all caps on a separate line with
no punctuation. The section ends where the next section begins.
The DEFINITION section contains declarations of data items (see below for data types and
syntax). The order in which items are defined is significant: declarations can only refer to
variables that were defined previously in the text file.
NOTE A large percentage of the SDL file is taken up by the DEFINITION section. See the
section on the C Pre-Processor and #include statements for ways to reduce the bulk of
the SDL file and increase clarity.
49
Render Parameters
The renderer is controlled by parameters in the SDL file. You can override many of the
parameters in the SDL file with command-line options. These parameters are included in
the DEFINITION section.
NOTE Most of the parame-ters are available as System Defined Variables on page 389 for use in
other parts of SDL.
The name of the output file can be specified on the command line or included in the camera
definition (since each camera outputs its own view of the scene). See the description of
Camera data types for more information.
DEFINITION section variable
command line equivalent
aalevelmax on page 390
-a amount
aalevelmin on page 390
aathreshold on page 390
-t amount
animation on page 56
byextension on page 57
-B by
byframe on page 57
-b by
composite_rendering on page 58
coverage_threshold on page 59
create on page 60
endframe on page 61
-e end
even on page 62
extensionsize on page 63
-E size
50 | Chapter 3 DEFINITION Section
DEFINITION section variable
command line equivalent
fast_shading on page 63
-Z switch
fields on page 64
grid_cache on page 65
hidden_line on page 65
hline_fill_color on page 67
hline_from_global on page 66
hline_isoparam_U on page 68
hline_isoparam_V on page 68
hline_line_color on page 67
hline_to_fill_color on page 66
ignore_filmgate on page 68
image_format on page 69
matte on page 70
-m mattefilename
max_reflections on page 71
max_refractions on page 72
max_shadow_level on page 73
motion_blur_on on page 74
odd on page 74
| 51
DEFINITION section variable
command line equivalent
odd_field_first on page 75
output on page 76
-p pixfilename
post_filter on page 79
post_center on page 78
post_adjacent on page 77
post_diagonal on page 78
preview_ray_trace on page 79
quiet on page 80
-q switch
resolution on page 81
show_particles on page 81
shutter_angle on page 82
small_features on page 84 (obsolete function)
simulation_substeps on page 83
simulation_frames_per_second on page
83
startextension on page 84
-S start
startframe on page 85
-s start
stereo on page 86
52 | Chapter 3 DEFINITION Section
DEFINITION section variable
command line equivalent
stereo_eye_offset on page 87
subdivision_control on page 87
subdivision_recursion_limit on page 89
textures_active on page 90
up on page 91
use_saved_geometry on page 92
-G
use_wavefront_depth on page 91
version on page 93
xleft on page 93
-x pixel
xright on page 94
-w wide
yhigh on page 95
-h high
ylow on page 96
-y pixel
aalevelmax
Syntax:
aalevelmax = <integer> ;
Option:
-a
aalevelmax | 53
Range:
0 to 6. If a different value is specified, the system will use the next highest
valid number, or 6 if the number input is too large. No message is given.
Default:
1
Purpose:
Determines the maximum number of subdivisions of a pixel.
Comments:
This limits the maximum number of subdivisions (rays), but does not
determine the actual number used. That number depends upon aathreshold
on page 55 and upon the actual scene being rendered. That is, the anti-aliasing
is performed adaptively, and only the rays (subdivisions) required to meet the
specified criteria are cre-ated.
Set aalevelmax to 0 for no anti-aliasing, and to 4 for a production level.
Example:
aalevelmax = 4;
aalevelmin
Syntax:
aalevelmin = <integer> ;
Option:
None
Range:
0 to 6. If a different value is specified, the system will use the next highest
valid number, or 6 if the number input is too large. No message is given.
54 | Chapter 3 DEFINITION Section
Default:
1
Purpose:
Determines the minimum number of subdivisions of a pixel.
Comments:
This limits the minimum number of subdivisions (rays), but does not determine
the actual number used. That number depends upon aathreshold on page 55
and upon the actual scene being rendered. That is, the anti-aliasing is
performed adaptively, and only the rays (subdivisions) required to meet the
specified criteria are cre-ated.
A setting of 0 prevents subdivision and generates 1 ray for each pixel. A setting
of 1 also prevents subdivision, but generates 4 rays for each pixel. A setting
of 2 allows 1 subdivision and up to 9 rays for each pixel. A setting of 4 allows
2 sub-divisions and up to 25 rays for each pixel. A setting of 8 allows 3
subdivisions and up to 81 rays for each pixel.
Example:
aalevelmin = 2;
aathreshold
Syntax:
aathreshold = <float> ;
Option:
-t <amount>
Range:
0 to 1. Values less than 0 are adjusted up to 0. Values greater than 1 are
ad-justed down to 1. No messages are given when adjusting.
aathreshold | 55
Default:
0.5
Purpose:
This statement determines the threshold for anti-aliasing.
Comments:
Set it to 0.5 for production-level anti-aliasing, especially when working with
sub-tle differences in shading. Set it to 1 if the picture shows high contrast.
When set to a high threshold, less anti-aliasing is performed, resulting in
quicker ren-dering. A set-ting of 0 forces maximum pixel subdivision
everywhere.
Example:
aathreshold = 60;
animation
Syntax:
animation = <scalar> ;
Range:
0 (FALSE) to non-zero (TRUE)
Default:
FALSE
Purpose:
To allow output of frame extensions on file names, even when only a single
frame is being rendered.
Example:
animation = TRUE;
56 | Chapter 3 DEFINITION Section
byextension
Syntax:
byextension = <integer> ;
Option:
-B <by>
Range:
Unbounded integer.
Default:
Rounded down integer from byframe, and if that value is 0, byextension is
set to 1.
Purpose:
To determine the pix file skip extension factor.
Comments:
This is used in conjunction with startextension on page 84 and extensionsize
on page 63 to label the output pix files with a different extension from the
frame number. If the value given to byextension on page 57 is a float, it is
rounded to the nearest lower integer.
Example:
byextension = 2;
byframe
Syntax:
byframe = <float> ;
byextension | 57
Option:
-b <by>
Range:
Unbounded.
Default:
1
Purpose:
This determines the frame skip factor.
Comments:
This is used in conjunction with startframe on page 85 and endframe on page
61 to determine the tem-poral extent of the rendering. If the skip factor is set
to 1, every frame is rendered. If it is set to 2, every second frame is rendered.
If it is set to -1, frames will be ren-dered in re-verse order.
Example:
byframe = -0.5;
composite_rendering
Syntax:
composite_rendering = <boolean>;
Range:
ON or OFF
Default:
OFF
58 | Chapter 3 DEFINITION Section
Purpose:
To create images that are not anti-aliased against a background.
Comments:
If set to ON, objects that are rendered will not be anti-aliased against the
background. For example, a pixel on the edge of an object will not be mixed
with black; only the subsamples actually striking the object will be used to
compute the color of the pixel. In TIFF terms, this button generates
unassociated alpha.
Example:
composite_rendering = OFF;
coverage_threshold
Syntax:
coverage_threshold = <float>;
Range:
0 to 1
Default:
0.5
Purpose:
To set a threshold of subsamples required for the pixel as a whole to be
considered part of the object and not part of the background.
Comments:
For example, if coverage threshold is set to 0.5 (50%) then at least half of the
subsamples must strike the object, or it will be considered as a “missed ray”
coverage_threshold | 59
determined by the mask generated by the renderer. This actually lets you
control the “bleed” around the edges of a sprite.
■
This feature is very important for games design, as all current games systems
have no way to alpha-blend a sprite into a background—sprite pixels are
either ON or OFF.
■
For image compositing, Coverage Threshold should be set to 0.0.
Used only if composite_rendering on page 58 = ON.
Example:
coverage_threshold = 0.5
create
Syntax:
create [shader|light|texture] (model = <name>, filename = "<filename>.o" );
Range:
Not applicable.
Default:
Not applicable.
Purpose:
After the create statement is placed in an SDL file, the OpenRender model
specified by the create statement can be used just like an AliasStudio model.
Comments:
See the OpenRender document for more details.
60 | Chapter 3 DEFINITION Section
Example:
create shader ( model = new_shader, filename = "new_shader.o" );
.
.
.
shader grey (
model
= new_shader,
lcolor
= (150, 150, 150),
ldiffuse = 0.8,
glow
= (20, 20, 180)
);
endframe
Syntax:
endframe = <float> ;
Option:
-e <end>
Range:
Unbounded.
Default:
1
Purpose:
This determines the last frame to be rendered.
Comments:
This is used in conjunction with startframe on page 85 and byframe on page
57 to determine the tempo-ral extent of the rendering.
endframe | 61
Example:
endframe = 50;
even
Syntax:
even = <scalar>;
Option:
None
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Purpose:
To allow individual control over the rendering of the even fields on page 64
of an animation. This will be useful if the animation has already been rendered
on frames and the user wishes to improve the quality of the animation, but
does not wish to re-render those fields which are already rendered as part of
the frames.
Comments:
These values are not animatable. They may not be overridden.
Example:
even = TRUE;
62 | Chapter 3 DEFINITION Section
extensionsize
Syntax:
extensionsize = <integer>;
Option:
-E <size>
Range:
Unbounded integer.
Default:
1
Purpose:
This determines the minimum number of digits in the pix file extension.
Comments:
This is used in conjunction with startextension on page 84 and byextension
on page 57 to label the files output by the renderer when animating with a
different extension from the frame number. If the value given to extensionsize
is a float, it is rounded to the nearest lower integer.
Example:
extensionsize = 3;
will create <pixfile>.001 for the first frame of an animation.
fast_shading
Syntax:
fast_shading <scalar>
extensionsize | 63
Option:
-Z <fast_shading>
Range:
0 (OFF) or non-0 (ON)
fast_shading is obsolete, and ignored in V7.5.
fields
Syntax:
fields = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default
FALSE
Purpose:
To turn on the rendering on fields option of the renderer (raycast or raytrace
only at the moment). If this component is TRUE, the output image files will
be of the form: <filename>.<frame>[oe] where the “o” extension stands for
odd on page 74 (the field containing the first scanline of the frame) and the
“e” extension stands for even on page 62 (the field con-taining the second
scanline of the frame).
Comments:
This component is not animatable. It may not be overridden.
Example:
fields = TRUE
64 | Chapter 3 DEFINITION Section
grid_cache
Syntax:
grid_cache = <integer>;
Range:
useful: 700 to 4000;
actual: 100 to infinity
Default:
4000
Purpose:
To reduce the amount of memory being used by the RayTracer, at the expense
of some speed. With all of the recursive subdivision in the RayTracer, a large
amount of memory can be used up in storing grids which undergo heavy use
at the start of a ray trace, but are not used at all later on in the process. These
grids and their associated memory may be reused to reduce the amount of
memory required by the ray tracer.
The ray tracer keeps an time ordered list of all the grids in the scene, based
on a Least Recently Used criteria. If grid_cache is set to some small integer
(say 600), then after 600 grids have been allocated, the Least Recently used
grid will be freed and that memory will be reused to store the next grid created.
This is not a data destructive process; the triangles in the freed grid are simply
placed back into the larger voxel which held the grid. That voxel may be
subdivided again should another ray enter that voxel in the future of the ray
trace.
This option is ignored by the PowerTracer, RayCaster, and PowerCaster.
hidden_line
Syntax:
hidden_line = <boolean>
grid_cache | 65
Range:
0 (OFF) or 1 (ON)
Default:
OFF
Purpose:
The hidden_line flag is used when hidden line rendering is desired.
hline_from_global
Syntax:
hline_from_global = <boolean>
Range:
0 (off) or 1 (ON)
Default:
OFF
Purpose:
hline_from_global lets you set the hline_fill_color on page 67, hline_line_color
on page 67, and number of patch lines (hline_isoparam_U on page 68,
hline_isoparam_V on page 68) for all surfaces in a hidden line rendering. In
order to use them, both hidden_line on page 65 and hline_from_global must
be set to ON.
hline_to_fill_color
Syntax:
hline_to_fill_color = <boolean>
66 | Chapter 3 DEFINITION Section
Range:
0 (OFF) or 1 (ON)
Default:
OFF
Purpose:
Use hline_to_fill_color to fill all surfaces in the scene with the hline_fill_color
on page 67. When set to OFF, hline_to_fill_color fills all surfaces in the scene
with the background color, as though the surfaces were transparent.
hline_fill_color
Syntax:
hline_fill_color = <triple>
Range:
effectively, 0-255 for R, G, B.
Purpose:
Defines the color of the filled regions for all surfaces in the scene, if
hline_to_fill_color on page 66 is set to ON.
hline_line_color
Syntax:
hline_line_color = <triple>
Range:
effectively, 0-255 for R, G, B.
hline_fill_color | 67
Purpose:
Defines the color of the lines for all surfaces in the scene.
hline_isoparam_U
Syntax:
hline_isoparam_U = <integer>
Range:
0 to infinity
Purpose:
Controls the number of lines shown in the U direction of each surface in the
scene. When set to 0, no lines are drawn on the surface other than edges.
hline_isoparam_V
Syntax:
hline_isoparam_U = <integer>
Range:
0 to infinity
Purpose:
Controls the number of lines shown in the V direction of each surface in the
scene. When set to 0, no lines are drawn on the surface other than edges.
ignore_filmgate
Syntax:
ignore_filmgate = <scalar>
68 | Chapter 3 DEFINITION Section
Range:
0 (OFF) or 1 (ON)
Default:
OFF
Purpose:
If there is a mismatch in the filmback aspect ratio and the rendering aspect
ratio, there can be a region outside the filmback in the rendered image . When
ignore_filmgate is OFF, this region is rendered black. If not, this region is
rendered with the usual geometry as if the boundary did not exist.
Example:
ignore_filmgate = OFF;
image_format
Syntax:
image_format= <string>
Range:
One of ALIAS|TIFF|TIFF16|RLA|FIDO|HARRY||SGI
Default:
ALIAS
Purpose:
To specify output format of generated images. In addition to the ALIAS file
format, we support TIFF and TIFF16, where the latter format contains 16 bits
of information per red, green, blue and alpha. Furthermore, we support
Wavefront’s RLA, Harry Quantel (HARRY), Fido Cineon (FIDO), and SGI.
image_format | 69
Example:
image_format = ALIAS;
matte
Syntax:
matte = <filename> ;
Option:
-m <filename>
Default:
Special — see below.
Purpose:
This determines the name of the output matte file created by the renderer.
Comments:
Each camera in the model is capable of producing output. Therefore, each
such cam-era must have the destination of that output specified. That is done
by means of the pix and mask components of each camera. Setting the output
destination with the matte parameter will apply only to the first camera.
Subsequent cameras must have the components specified. The matte parameter
is included simply for compatibility with previous versions of SDL. Users are
encouraged to use the camera components instead. See the description of
those components for the de-faults used, and for the order of priority among
the command line option, the components, and the matte pa-rameter.
The matte file specifies how the image must be weighted when compositing.
When using a matte for compositing against another image, the scene should
be rendered with composite_rendering = TRUE..
The <filename> can be a full or relative UNIX pathname. Relative path names
are applied with respect to the current working directory when the renderer
is in-voked.
When animating several frames in an animated sequence from a single SDL
file, the number of files (and their names) depends upon the renderer.
70 | Chapter 3 DEFINITION Section
For the Raycaster or the Raytracer, a series of files with names in the form
<filename>.<integer> are created. Note that this extension is in addition to
(and ap-plied after) any other extension that may exist as a result of using a
filename variable.
matte output is ignored when using the wireframer.
Example:
matte = "mask/blue_screen", frame;
max_reflections
Syntax:
max_reflections = <scalar> ;
Option:
None
Range:
Non-negative.
Default:
10
Purpose:
This limits the number of reflection rays that may be created.
Comments:
Ray tracing is a recursive process. Each ray bounces off of reflective objects.
This parameter allows the user to limit the number of bounces a ray may take
on a global basis. The global limit is pro-vided so that users may produce a
quick and dirty image to check the layout and/or texturing of the scene without
having to do a major edit of the SDL file. The global limit will only take effect
if it is LESS than the limit for the relevant shader, otherwise the shader’s limit
will be respected. The parameter is only use-ful, therefore, for reducing image
quality, not increasing it.
max_reflections | 71
Example:
A user wants to RayTrace an SDL file that has highly reflective surfaces with
a re-flec-tion limit of 6. He is not sure, however, of the placement of the objects
and wishes to do a quick test. So, the user sets the max_reflections = 1. When
a ray hits a surface with a reflection limit of 6, a reflection ray will be traced
only if the ray is a primary ray (i.e., its level is less than the value of
max_reflections).
If, on the other hand, a primary ray hits an object with a reflection limit of
0, no re-flected ray will be traced. This is because although the parameter
max_reflections specifies that a ray of level 0 may bounce off of a surface, the
surface itself does not allow ANY rays to bounce off of it.
max_refractions
Syntax:
max_refractions = <scalar> ;
Option:
None
Range:
Non-negative.
Default:
10
Purpose:
This limits the number of refraction rays that may be created.
Comments:
RayTracing is a recursive process. Each ray refracts through transparent objects.
This parameter allows the user to limit the propagation of such rays on a global
basis. The global limit is provided so that users may produce a quick image
to check the layout and/or texturing of the scene without having to do a major
edit of the SDL file. The global limit will only take effect if it is LESS than the
72 | Chapter 3 DEFINITION Section
limit for the relevant shader, otherwise the shader’s limit will be respected.
The parameter is only useful, therefore, for reducing image quality, not
increas-ing it.
Example:
max_refractions = 2;
max_shadow_level
Syntax:
max_shadow_level = <scalar> ;
Option:
None
Range:
-1 to infinity.
Default:
10
Purpose:
This limits the number of shadow rays that may be created.
Comments:
RayTracing is a recursive process. Each ray creates bundles of shadow rays (one
for each shadow casting light). The user can control whether or not these rays
are created on a global basis. The global limit is provided so that users may
produce a quick image to check the lay-out and/or texturing of the scene with
out having to do a major edit of the SDL file. The global limit will only take
effect if it is LESS than the limit for the relevant shader, otherwise the shader’s
limit will be respected. The parameter is therefore only useful for reducing
image quality, not increasing it.
max_shadow_level | 73
Shadow rays are defined to have the same level as the incident ray. Setting
max_shadow_level = 0, for example, will only trace shadow rays from primary
ray intersections (which by definition are level 0 rays).
Example:
max_shadow_level = 0;
motion_blur_on
Syntax:
motion_blur_on= <scalar>
Range:
0 (FALSE) to non-zero (TRUE)
Default:
FALSE
Purpose:
To blur visible parts of moving objects across the film plane. Note that if this
global flag is FALSE, no motion blur will take place, regardless of whether
specific objects or cameras have motion_blur set ON.
Example:
motion_blur_on= TRUE;
odd
Syntax:
odd = <scalar>;
Option:
None
74 | Chapter 3 DEFINITION Section
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Purpose:
To allow individual control over the rendering of the odd fields on page 64
of an ani-mation. This will be useful if the animation has already been rendered
on frames and the user wishes to improve the quality of the animation, but
does not wish to re-ren-der those fields which are already rendered as part of
the frames.
Comments:
These values are not animatable. They may not be overridden.
Example:
odd = FALSE;
odd_field_first
Syntax:
odd_field_first = <scalar>;
Option:
None
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
odd_field_first | 75
Purpose:
This parameter is only relevant when fields on page 64 rendering is turned
on. Once turned on, there needs to be the knowledge as to which frame should
come first (time-wise), be it odd or even scanlines.
Comments:
These values are not animatable. They may not be overridden.
Example:
odd_field_first = FALSE;
output
Syntax:
output = <filename> ;
Option:
-p <filename>
Default:
Special — see below.
Purpose:
This determines the name of the output image file created by the renderer.
Comments:
Each camera in the model is capable of producing output. Therefore, each
such cam-era must have the destination of that output specified. That is done
by means of the pix on page 160and mask on page 154 components of each
camera. Setting the output destination with the output parameter will apply
only to the first camera. Subsequent cameras must have the components
specified. The output parameter is included simply for compatibility with
previous versions of SDL. Users are encouraged to use the camera components
instead. See the description of those Camera Data Type on page 140components
76 | Chapter 3 DEFINITION Section
for the defaults used, and for the order of priority among the command line
option, the components, and the output parameter.
The <filename> can be a full or relative UNIX pathname. Relative path names
are applied with respect to the current working directory when the renderer
is invoked.
When animating several frames in an animated sequence from a single SDL
file, the number of files (and their names) depends upon the renderer.
For the Raycaster or the Raytracer, a series of files with names in the form
<filename>.<integer> are created. Note that this extension is in addition to
(and ap-plied after) any other extension that may exist as a result of using a
filename variable.
For the wireframer a single file is produced containing all frames.
Example:
output = ("pix/bike") ;
post_adjacent
Syntax:
post_adjacentr= <scalar>
Range:
0 to 20
Default:
1
Purpose:
The value in this slider represents the edge pixel weights for a 3 by 3 pixel
post-process Bartlet filter.
Example:
post_adjacent = 1;
post_adjacent | 77
post_center
Syntax:
post_center= <scalar>
Range:
0 to 20
Default:
8
Purpose:
The value in this slider represents the center pixel weight for a 3 by 3 pixel
post-process Bartlet filter.
Example:
post_center = 8;
post_diagonal
Syntax:
post_diagonal= <scalar>
Range:
0 to 20
Default:
1
Purpose:
The value in this slider represents the corner pixel weights for a 3 by 3 pixel
post-process Bartlet filter.
78 | Chapter 3 DEFINITION Section
Example:
post_diagonal = 1;
post_filter
Syntax:
post_filter= <scalar>
Range:
0 (FALSE) to non-zero (TRUE)
Default:
FALSE
Purpose:
Executes a 3x3 filter of image after it has been rendered.
Example:
post_filter= TRUE;
preview_ray_trace
Syntax:
preview_ray_trace = <scalar>;
Range:
0 (false) to non-zero (true)
Default:
1 (true)
post_filter | 79
Purpose
To generate a sample postage stamp-sized RayTrace of the image (100 by 100
pixels). This preview will generate time and memory estimates for the RayTrace.
quiet
Syntax:
quiet = <scalar> ;
Option:
-q <switch>
Range:
Boolean (TRUE/FALSE)
Default:
0 (FALSE)
Purpose:
This allows control of the message output from the renderer.
Comments:
When quiet = FALSE is specified, the renderer produces normal message (error,
warning and information) output directed to “stderr”. When quiet = TRUE is
speci-fied, the renderer does not produce diagnostic output.
Example:
quiet = TRUE;
80 | Chapter 3 DEFINITION Section
resolution
Syntax:
resolution = <scalar> <scalar>;
Range:
Positive integers
Default:
645 486
Purpose:
To specify the size of the defined image (not necessarily what is rendered).
Necessary so that backgrounds, image planes, etc. can be matched.
Comments:
With the new camera controls (such as film back offset), the viewport on page
167 need not always be the same size (or even shape) as the image being defined.
Other controls (xleft on page 391, yhigh on page 392, and so on) can direct the
renderer to only render a portion of the whole image. The resolution statement
defines the image. Numbers are in pixels.
Example:
resolution = 645 486;
show_particles
Syntax:
show_particles = <boolean>;
Range:
Boolean (TRUE/FALSE)
resolution | 81
Default:
TRUE
Purpose:
To indicate whether or not to render particles.
Example:
show_particles = TRUE;
shutter_angle
Syntax:
shutter_angle= <floating_point>
Range:
1 to 360
Default:
144
Purpose:
To determine the shutter angle size (in degrees) when motion_blur on page
182 is on.
The greater the number of degrees, the more motion blur is applied. For
example, setting the shutter angle to 180 degrees will sample the objects over
half of the frame step time.
When set to OFF, motion blur is not calculated, regardless of whether or not
motion blur is turned on for objects and cameras.
NOTE Motion blur is available only with the RayCaster and PowerCaster. World
space texture mapping will not work with motion blur.
82 | Chapter 3 DEFINITION Section
Example:
shutter_angle = 144;
simulation_substeps
Syntax:
simulation_substeps = <integer>
Range:
1 to 8
Default:
1
Purpose:
To control the accuracy of the particle simulation, most notably when particle
collisions are being calculated. If this number is small, particles may fail to
detect collisions with moving objects, or appear to bounce off objects at the
wrong time. Increasing the number of substeps will produce a more accurate
animation, but will also increase the amount of time needed to render each
frame.
Example:
simulation_substeps = 5
simulation_frames_per_second
Syntax:
simulation_frames_per_second = <integer>
Range:
1 to 30
simulation_substeps | 83
Default:
30
Purpose:
To specify how fast the images will be displayed from the final animation.
This value is used to calculate the correct amount of force and gravity to apply
to particles during the simulation.
Example:
simulation_frames_per_second = 15
small_features
Syntax:
small_features = <scalar>;
Range
0 (false) to non-zero (true).
Default:
0 (false).
Note that small_features has been obsolete since V5.1. Its presence in SDL is
ignored.
startextension
Syntax:
startextension = <integer>;
Option:
-S <start>
84 | Chapter 3 DEFINITION Section
Range:
Unbounded integer.
Default:
Rounded down integer from startframe.
Purpose:
To specify the starting extension number of the output pix file for an
animation.
Comments:
Useful for occasions when the byframe on page 57 and/or startframe on page
85 of an animation are non-integer and you want the files to be numbered
as integers when output by the renderer.
Example:
startextension = 4;
startframe
Syntax:
startframe = <float> ;
Option:
-s <start>
Range:
Unbounded.
Default:
1
startframe | 85
Purpose:
This determines the first frame to be rendered.
Comments:
This is used in conjunction with endframe on page 61 and byframe on page
57 to determine the tempo-ral extent of the rendering.
Example:
startframe = 300;
stereo
Syntax:
stereo = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
FALSE
Purpose:
The stereo flag specifies if all the cameras in the SDL file are to render a stereo
pair of images.
Comments:
This value may not be animated. This can be used in conjunction with fields.
See also stereo_eye_offset on page 87.
Note: this will cause two sets of files to be output for each camera. The output
file names will be suffixed with “_LEFT” and “_RIGHT”.
Example:
stereo = TRUE;
86 | Chapter 3 DEFINITION Section
stereo_eye_offset
Syntax:
stereo_eye_offset = <scalar>
Default:
0.5
Purpose:
To specify the eye separation between the eye points of two cameras that will
be used to render the stereo pair. The offset is in world coordinates and specifies
the eye’s off-set in X. See “Creating Rendered Stereo Pairs on page 519” tutorial
for a more detailed description.
Comments:
This component is animatable. Although this component has a default, it is
wise to specify it since the magnitude of the offset depends on the scale of
the scene. See the Stereo tutorial for a more detailed description.
Example:
stereo_eye_offset = 3.0
subdivision_control
Syntax:
subdivision_control = ( ( <scalar> ,<triple> ), (<scalar> , <triple> ),
.
.
.
( <scalar> , <triple> ) ) ;
stereo_eye_offset | 87
Option
None.
Range:
None.
Default:
See format in example:
(20, 3, 3, 3)
(40, 4, 4, 4)
(100, 6, 6, 5)
(500, 6, 6, 8)
(1000, 10, 10, 10)
(2000, 20, 20, 20)
(5000, 10, 10, 10)
Purpose:
This controls how spatial subdivision will function for the RayTracer.
Comments:
This is probably the most complicated control for the user to understand, but
it allows the sophisticated user to experiment with different types of spatial
subdi-vision for RayTracing his model.
The RayTracer subdivides world space into voxels. Each voxel is a parallelpiped
ori-ented parallel to the modeling space axes. All of space is initially contained
in one large voxel. When triangles are created to approximate the geometry
of the scene, they are stored in the voxel. After all the geometry is defined,
the number of triangles in the voxel is used to determine if the voxel should
be subdivided or not. If the voxel should be subdivided, how should the
subdivision be per-formed? These issues of when and how for subdivision are
specified by the sub-division_control parameter.
The control is in the form of a list of entries. Each entry contains two parts
— a <scalar> and a <triple>.
88 | Chapter 3 DEFINITION Section
The <scalar> part controls when to subdivide, the <triple> part controls how.
The list may have any number of entries. The first entry in the list defines a
range from zero to the value of the <scalar>. If the number of triangles in the
voxel is in this range, then the voxel is not subdivided. The second entry in
the list also defines a range, this time from the end of the previ-ous range to
the value of this entry’s <scalar>. If the number of triangles in the voxel is in
this second range, then the voxel is subdivided by using the <triple> of the
previous (first) entry.
The subdi-vision is performed by simply dividing the voxel into equal sized
pieces, where the number of pieces in each of the x,y & z dimensions is given
by the <triple>. Thus, the <scalar> defines the high end of a range, with the
first range starting at zero and sub-sequent ranges starting where their
predecessor left off. The <triple> defines the number of subdivisions to be
made in each dimension when the number of triangles falls in the range
follow-ing that defined by the <scalar>. The <triple> for the last en-try,
therefore, is used when the number of triangles exceeds the last <scalar> given.
Conversely, if the number of triangles is less than the first <scalar> given, then
no subdivision is performed.
The process of subdivision is recursively applied to each voxel created by the
subdi-vision of the initial voxel until no further such subdivision is possible.
Example:
subdivision_control = ( ( 8, (3,3,3) ),
( 30, (4,4,4) ),
( 100, (6,6,5) ),
( 500, (6,6,8) ),
( 1000, (10,10,10) ),
( 2000, (20,20,20) ),
( 5000, (10,10,10) ) ) ;
subdivision_recursion_limit
Syntax:
subdivision_recursion_limit = <scalar> ;
Option:
None
subdivision_recursion_limit | 89
Range:
Useful 1, 2, 3; actual 0 to infinity
Default:
2
Purpose:
The subdivision_recursion_limit limits the number of times the
subdivision_control on page 87 criteria may be applied to a voxel.
Comments:
It limits, indirectly, the amount of machine resources used. If there is a very
small volume with many, many triangles in it, then this will prevent the
RayTracer from recursing too much.
Example:
subdivision_recursion_limit = 2;
textures_active
Syntax:
textures_active= <scalar>
Range:
0 (FALSE) to non-zero (TRUE)
Default:
TRUE
Purpose:
If set to TRUE, all textures are used. If set to FALSE, no textures are used.
90 | Chapter 3 DEFINITION Section
Example:
textures_active = TRUE;
up
Syntax:
up = yaxis;
up = zaxis;
Default:
none
Purpose:
To make use of the coordinate system used in the modeler. yaxis is the standard
coordinate pointing up for video animators, while industrial designers tend
to use zaxis.
use_wavefront_depth
Syntax:
use_wavefront_depth = <scalar>;
Range
0 (false) to not 0 (TRUE)
Default:
FALSE
Purpose:
This parameter is only relevant if depth files are written out during rendering.
If turned to FALSE, then the depth file is the same Alias depth file it has always
been. If this is set to TRUE, then a depth file that is suitable for Composer is
written. This depth file is different from the standard Alias depth file, in that
use_wavefront_depth | 91
the depth is an unsigned short value that is normalized between the near and
far clipping planes.
use_saved_geometry
Syntax:
use_saved_geometry = <scalar>;
Range
0 (false) to not 0 (TRUE)
Option
-G# Turn saved geometry on (non-zero ‘#’) or off(0).
Default:
FALSE
Purpose
Saved geometry is useful for animations with complicated geometries that
take a long time to subdivide, such as trimmed surfaces, displacement mapped
geometry, or anything with a high subdivision. If use_saved_geometry is TRUE,
these surfaces are tesselated (subdivided into triangles) only once, and then
these triangles will be kept in memory and re-used next frame. Since the
triangles are saved, animation of some surface properties necessarily disallows
the saving of geometry. Metamorphosis is a prime example; since the geometry
changes from frame to frame, there is no point storing the geometry from
frame to frame. (See below for a complete list of operations that will invalidate
saved geometry.)
Saved geometry will NOT be applied on:
■
objects that have metamorphosis
■
objects that have subdivision levels which are not literal
■
objects with curvature shaders on them
92 | Chapter 3 DEFINITION Section
You MAY save geometry for an object with a displacement map shader on it,
however, if the user animates the displacement map, the saved geometry will
not change, and neither will the appearance of the object in the image.
You cannot stop and start a render process that uses Saved Geometry and
retain the saved geometry.
Saved Geometry uses a significant amount of memory. You should have at
least 100 megabytes of swap space available before attempting to use it.
version
Syntax:
version = <scalar>;
Range:
0.0 to 10.0
Default:
3.2.1
Purpose:
Identifies the AliasStudio version that created this SDL file. Note that the
default changes every release.
Example:
version = 3.2.1;
xleft
Syntax:
xleft = <integer> ;
Option:
-x <pixel>
version | 93
Range:
0 to 8190 (Must be less than xright). Interpreted as an integer.
Default:
0
Purpose:
Determines the left edge of the image on the screen.
Comments:
The xleft, xright on page 94, yhigh on page 95 and ylow on page 96 parameters
determine the actual pixels to be ren-dered. They do not affect the scene or
the view being rendered in any way, but are used to render a rectangular
portion of the view.
The rectangle selected must be valid.
That is: 0 <= xleft < xright, and 0 <= ylow < yhigh.
Example:
xleft = 128;
xright
Syntax:
xright = <integer> ;
Option:
-w <wide>
Range:
1 to 8191. Interpreted as an integer.
94 | Chapter 3 DEFINITION Section
Default:
644
Purpose:
Determines the right edge of the image on the screen.
Comments:
The xleft on page 93, xright, yhigh on page 95 and ylow on page 96 parameters
determine the actual pixels to be ren-dered. They do not affect the scene or
the view being rendered in any way, but rather, are used to render a rectangular
portion of the view.
The rectangle selected must be valid. That is: 0 <= xleft <xright, and 0 <= ylow
< yhigh.
Note that when specified in SDL, xright is an absolute number, but when
speci-fied on the command line, <wide> is the number of pixels of width of
the image (i.e., xright – xleft). This is so SDL retains the same sense as previous
versions and the same sense as the interactive package, while the command
line behavior is consistent with all the framebuffer standalones.
Example:
xright = 256;
yhigh
Syntax:
yhigh = <integer> ;
Option:
-h <high>
Range:
1 to 8191. Interpreted as an integer.
yhigh | 95
Default:
485
Purpose:
Determines the top of the image on the screen.
Comments:
The xleft on page 93, xright on page 94, yhigh and ylow on page 96 parameters
determine the actual pixels to be ren-dered. They do not affect the scene or
the view being rendered in any way, but are used to render a rectangular
portion of the view.
The rectangle selected must be valid. That is: 0 <= xleft <xright, and 0 <= ylow
<yhigh.
NOTE When specified in SDL, yhigh is an absolute number, but when speci-fied
on the command line, <high> is the number of pixels of height of the image (i.e.,
yhigh – ylow). This is so SDL retains the same sense as previous versions and the
same sense as the interactive package, while the command line behavior is
consistent with all the framebuffer standalones.
Example:
yhigh = 256;
ylow
Syntax:
ylow = <integer> ;
Option:
-y <pixel>
Range:
0 to 8190. Interpreted as an integer.
96 | Chapter 3 DEFINITION Section
Default:
0
Purpose:
Determines the bottom of the image on the screen.
Comments:
The xleft on page 93, xright on page 94, yhigh on page 95 and ylow parameters
determine the actual pixels to be ren-dered. They do not affect the scene or
the view being rendered in any way, but are used to render a rectangular
portion of the view.
The rectangle selected must be valid.
That is: 0 <= xleft <xright, and 0 <= ylow < yhigh.
Example:
ylow = 128;
ylow | 97
98
ENVIRONMENT Section
4
The ENVIRONMENT section (if it is included at all) contains definitions of environment
variables (the background of the scene: an image, a texture, or a color), atmospheric effects
(how light travels between objects), photographic effects, global dynamics variables, and
master lighting.
The ENVIRONMENT section is the place for definitions of:
■
the background
■
atmospheric effects
■
global parameters
■
photographic effects
The ENVIRONMENT section (if present) begins with the word ENVIRONMENT in all caps on
a separate line with no punctuation. The section ends where the next section begins.
The following items are described in this section:
■
background on page 101
■
fog on page 102
■
dynamics global parameters on page 103
■ gravity on page 103
■
air_density on page 104
■
Floor on page 104
■
floor_offset on page 105
■
ceiling on page 105
■
ceiling_offset on page 106
■
left on page 106
■
left_offset on page 107
99
■
■
■
right on page 107
■
right_offset on page 108
■
front on page 108
■
front on page 108
■
back on page 109
■
back_offset on page 110
■
wall_friction on page 110
■
wall_elasticity on page 111
■
turbulence_animated on page 111
■
turbulence_granularity on page 112
■
turbulence_intensity on page 112
■
turbulence_persistence on page 113
■
turbulence_roughness on page 113
■
turbulence_space_resolution on page 114
■
turbulence_spread on page 114
■
turbulence_time_resolution on page 115
■
turbulence_variability on page 115
photo_effects on page 116
■ auto_exposure on page 116
■
film_grain on page 117
■
filter on page 117
master_light on page 118
■ intensity on page 118
■
■
light_color on page 119
shader_glow on page 120
■ glow_color on page 120
■
glow_eccentricity on page 121
100 | Chapter 4 ENVIRONMENT Section
■
glow_opacity on page 122
■
glow_radial_noise on page 123
■
glow_star_level on page 123
■
glow_spread on page 124
■
glow_type on page 125
■
halo_color on page 125
■
halo_eccentricity on page 126
■
halo_radial_noise on page 127
■
halo_radial_noise on page 127
■
halo_spread on page 128
■
halo_star_level on page 129
■
halo_type on page 129
■
quality on page 130
■
radial_noise_frequency on page 131
■
star_points on page 132
■
threshold on page 132
background
Syntax:
background (backdrop = <filename>);
or
background (color = (r, g, b));
or
background (color = <texture>);
background | 101
Default:
none
Purpose:
The file filename could be a digitized image, a previously rendered screen, or
a painted image. It must be of the same size and resolution as the image being
ren-dered. This statement is animatable.
The background can be procedurally modeled, or it can be textured with a
file. For details of procedures, please see Procedural Textures and Natural
Phenomena on page 407.
If a file texture is used, it will be stretched to match the image dimensions.
Both RGB (24 bit) and scalar (8 bit) files can be used. Note that if you use an
8-bit file for the background, you will get a grey scale background.
This allows reflected environments to also be used for background.
NOTE The only type of backgrounds that will reflect or refract properly in the
AliasStudio Raytracer are environment maps. Color procedural backgrounds will
show up on reflective objects and will show through transparent objects, but the
results may look incorrect. Ramp and file backgrounds will not appear at all in
reflections or refractions. Otherwise, the background will look and act the same
as in the AliasStudio RayCaster when no objects are obscuring the background.
Environment map backgrounds are useful in the AliasStudio RayTracer. They
allow an object to reflect parts of itself by using the Raytracer, while saving
rendering time by creating the reflections of surrounding objects with a cubic
reflection map in the shader.
fog
Syntax:
fog (fogtype = <scalar>, ... );
Purpose:
This procedure creates the optical effect of fog between objects and the camera.
For further details on its use and associated arguments, see “Fog on page 412”
in the Procedural Textures and Natural Phenomena on page 407 chapter of this
manual, or refer to the RENDER ->Shader section of Rendering with AliasStudio.
102 | Chapter 4 ENVIRONMENT Section
dynamics global parameters
Syntax:
dynamics (
,
gravity = 1.0,
air_density = 0.05,
Floor = ON,
floor_offset = 0.0,
ceiling = OFF,
ceiling_offset = 20.0,
left = OFF,
left_offset = -10.0,
right = OFF,
right_offset = 10.0,
front = OFF,
front_offset = -10.0,
back = OFF,
back_offset = 10.0,
wall_friction = 0.0,
wall_elasticity = 0.707,
turbulence_intensity = 0.0,
turbulence_spread = 0.5,
turbulence_persistence = 5.0,
turbulence_animated = ON,
turbulence_space_resolution = 16,
turbulence_time_resolution = 16,
turbulence_roughness = 0.5,
turbulence_variability = 0.5,
turbulence_granularity = 0.0
);
gravity
Syntax:
gravity = <scalar>,
dynamics global parameters | 103
Range:
-infinity to infinity
Default:
1.0
Purpose:
This value represents the surface gravity of the planet. The units are in earth’s
gravity, so that earth surface = 1, moon =.18
air_density
Syntax:
air_density = <scalar>,
Range:
0 to infinity
Default:
1.0
Purpose:
This is the density of the atmosphere of the planet. 1 = water, 10 = goo,.001
is fairly air-like. This value affects the buoyancy of objects, and air drag on
objects.
Floor
Syntax:
Floor = <boolean>,
104 | Chapter 4 ENVIRONMENT Section
Range:
ON/OFF
Default:
ON
Purpose:
Turns the use of a Floor for Dynamics ON or OFF.
floor_offset
Syntax:
floor_offset = <scalar>,
Range:
-infinity to infinity
Default:
0.0
Purpose:
If there is a floor, the value determines at what point on the up-down axis it
exists (Z for z-up, Y for Y-up).
ceiling
Syntax:
ceiling = <boolean>,
Range:
ON/OFF
floor_offset | 105
Default:
OFF
Purpose:
Turns the use of a ceiling for Dynamics ON or OFF.
ceiling_offset
Syntax:
ceiling_offset = <scalar>,
Range:
-infinity to infinity
Default:
20.0
Purpose:
If there is a ceiling, the value determines at what point on the up-down axis
it exists (Z for z-up, Y for Y-up).
left
Syntax:
left = <boolean>,
Range:
ON/OFF
Default:
OFF
106 | Chapter 4 ENVIRONMENT Section
Purpose:
Turns the use of a left wall on or off for dynamics.
left_offset
Syntax:
left_offset = <scalar>,
Range:
-infinity to infinity
Default:
-10.0
Purpose:
If there is a left wall, the value determines at what point on the left-right axis
it exists (X for z-up, Z for Y-up).
right
Syntax:
right = <boolean>,
Range:
ON/OFF
Default:
OFF
Purpose:
Turns the use of a right wall on or off for Dynamics.
left_offset | 107
right_offset
Syntax:
right_offset = <scalar>,
Range:
-infinity to infinity
Default:
10.0
Purpose:
If there is a right wall, the value determines at what point on the left-right
axis it exists (X for z-up, Z for Y-up).
front
Syntax:
front = <boolean>,
Range:
ON/OFF
Default:
OFF
Purpose:
Turns the use of a front wall on or off for Dynamics.
108 | Chapter 4 ENVIRONMENT Section
front_offset
Syntax:
front_offset = <scalar>,
Range:
-infinity to infinity
Default:
-10.0
Purpose:
If there is a front wall, the value determines at what point on the front-back
axis it exists (Y for z-up, X for Y-up).
back
Syntax:
back = <boolean>,
Range:
ON/OFF
Default:
OFF
Purpose:
Turns the use of a back wall off or on for dynamics.
front_offset | 109
back_offset
Syntax:
back_offset = <scalar>,
Range:
-infinity to infinity
Default:
10.0
Purpose:
If there is a back wall, the value determines at what point on the front-back
axis it exists (Y for z-up, X for Y-up).
wall_friction
Syntax:
wall_friction = <scalar>,
Range:
0 to 1
Default:
0.5
Purpose:
This value represents the coefficient of friction for the walls. A value of 0
means no friction.
110 | Chapter 4 ENVIRONMENT Section
wall_elasticity
Syntax:
wall_elasticity = <scalar>,
Range:
infinity to infinity
Default:
0.5
Purpose:
This value determines the damping of speed on collision with a wall. A value
of 0 loses all speed, a value of 1 bounces back with same speed as before.
turbulence_animated
Syntax:
turbulence_animated = <boolean>,
Range:
ON/OFF
Default:
ON
Purpose:
The turbulence may be static, or it may vary over time. With static turbulence,
you get dappled lighting but it doesn’t change. With animated turbulence,
you get flickering light. In a static turbulent wind field, the eddies are always
in the same place: a stream of particles blowing through a static field would
always follow the same path. In an animated field, the path itself would swirl
and change.
wall_elasticity | 111
turbulence_granularity
Syntax:
turbulence_granularity = <scalar>,
Range:
0 to 1.0
Default:
0.0
Purpose:
This value defines the Low frequency cutoff. It is like a high pass filter. It
allows for grainy patterns of turbulence.
turbulence_intensity
Syntax:
turbulence_intensity = <scalar>,
Range:
-infinity to infinity
Default:
0.0
Purpose:
This defines the degree to which a volume light is turbulent. The light or force
direction is modified by the turbulence, such that when the
turbulence_intensity = 1.0 then the direction is totally the direction calculated
by the turbulence. When the turbulence_intensity = 0.5, then the direction
will be a 50/50 blend of turbulence and light. In the case of the default
112 | Chapter 4 ENVIRONMENT Section
SPHERE_VOLUME shape, a value of 0.5 would cause objects to move generally
away from the light, but in a turbulent fashion.
If the turbulence_intensity = 1, then objects would just swirl around in no
particular direction. The decay of the light is respected, however, so the objects
would swirl more vigorously near the light source. If you wish to increase the
general level of force you must use the light intensity or force_intensity
parameter. Note that this differs from the turbulence_intensity in the
Environment dynamics section, as that value controls the overall intensity of
force.
turbulence_persistence
Syntax:
turbulence_persistence = <scalar>,
Range:
0 to infinity
Default:
5.0
Purpose:
This value represents the time scale. Stretch out the turbulence so that it
changes more slowly.
turbulence_roughness
Syntax:
turbulence_roughness = <scalar>,
Range:
0 to 1.0
turbulence_persistence | 113
Default:
0.5
Purpose:
This value defines the High Frequency cutoff for the spatial portion of the
Fourier spectrum. It is like a low-pass filter.
turbulence_space_resolution
Syntax:
turbulence_space_resolution = <scalar>,
Range:
1 to 16
Default:
16
Purpose:
This defines how large the table is in X, Y, Z. Turbulence patterns match at
the edges of the turbulence box, so that this pattern is repeated seamlessly
throughout the range of the volume light.
turbulence_spread
Syntax:
turbulence_spread = <scalar>,
Range:
-infinity to infinity
114 | Chapter 4 ENVIRONMENT Section
Default:
0.5
Purpose:
This value represents the space scale. Scale the turbulence box so that the
same amount of turbulence covers a larger volume.
turbulence_time_resolution
Syntax:
turbulence_time_resolution = <scalar>,
Range:
2 to 32
Default:
16
Purpose:
For animated turbulence, this defines the resolution in time. (i.e. this many
3-D tables are created).
turbulence_variability
Syntax:
turbulence_variability = <scalar>,
Range:
0 to 1.0
Default:
0.5
turbulence_time_resolution | 115
Purpose:
This value defines the High Frequency cutoff for the time portion of the Fourier
spectrum.
photo_effects
Syntax:
photo_effects (
,
auto_exposure = false,
film_grain = 0.0,
filter = (255.0, 255.0, 255.0)
);
auto_exposure
Syntax:
auto_exposure=true/false
Default:
true
Purpose:
Use auto_exposure to adjust the amount of apparent light that enters the
camera. If you are using shader glow on an object entering a scene, the light
level in the scene may change drastically. With auto_exposure set to true (the
default), the amount of glow seen on the object can fluctuate. If this is the
case, try using auto_exposure set to false.
auto_exposure only affects glow.
You may have to adjust the glow_color on page 120on the shader if you turn
auto_exposure off. Do this by increasing the values above 255 (the normal
limits for the color).
116 | Chapter 4 ENVIRONMENT Section
Example:
auto_exposure=false
film_grain
Syntax:
film_grain = <scalar>
Range:
Non-negative
Default:
0.0
Purpose:
This simulates the way film grains modify the color of an image.
Comments:
This component may be animated.
Example:
film_grain = 0.1
filter
Syntax:
filter = <color>
Range:
Non-negative
film_grain | 117
Default:
(255,255,255)
Purpose:
This color is applied as a scale of the image color, simulating a camera filter.
Texture maps may also be used. For example a ramp from blue to white will
make the top of the image more blue.
Comments:
Values greater than 255 can be used to enhance overall scene contrast and
brightness.
Example:
filter = (255,200,100)
master_light
Syntax:
master_light (
,
intensity = 1.0,
light_color = (255.0, 255.0, 255.0)
);
intensity
Syntax:
intensity = <scalar>
Range:
Any floating point number.
118 | Chapter 4 ENVIRONMENT Section
Default:
1.0
Purpose:
This is a multiplier for the intensity of all lights in the scene. If the value is 2,
then the overall lighting will be twice as bright. If the value is .5, then the
overall lighting will be half as bright.
Example:
intensity = 1.2
light_color
Syntax:
filter = <color>
Range:
Any floating point numbers.
Default:
(255,255,255)
Purpose:
This modifies the overall light color in a scene. If the value is (255,200,200)
then the overall scene lighting will be more red.
Example:
light_color = (30, 255, 200)
light_color | 119
shader_glow
Syntax:
shader_glow (
,
glow_type = LINEAR_GLOW,
halo_type = LINEAR_GLOW,
quality = 0.5,
threshold = 0.0,
glow_color = (100.0, 100.0, 100.0),
glow_spread = 0.05,
glow_eccentricity = 0.1,
glow_radial_noise = 0.0,
glow_star_level = 0.0,
glow_opacity = 0.0,
halo_color = (100.0, 100.0, 100.0),
halo_spread = 0.3,
halo_eccentricity = 0.1,
halo_radial_noise = 0.0,
halo_star_level = 0.0,
halo_lens_flare = 0.0,
rotation = 0.0,
radial_noise_frequency = 0.5,
star_points = 4.0
);
glow_color
Syntax:
glow_color = <color>
Range:
Any floating point values.
Default:
(100,100,100)
120 | Chapter 4 ENVIRONMENT Section
Purpose:
To set the color and brightness for the glow effect. To create very bright glows,
set the glow color high, for example(400,400,400). Setting the glow brightness
on the shader should be used to set only the brightness relative to other
shaders, whereas the glow_color should be used to set the overall brightness
of the glow effect.
Comments:
This parameter may be texture mapped( a circular or radial ramp texture is
particularily useful ). If this this texture mapped, then then texture will appear
around glowing objects. The smaller the source of the glow, the more "focused"
the image of the texture will appear. If the glow_eccentricity on page 121
parameter is set to 1.0 then the full texture will be more visible.
Example:
glow_color = ( 300, 200, 100 )
glow_eccentricity
Syntax:
glow_eccentricity = <scalar>
Range:
Any non-negative number
Default:
0.1
Purpose:
This determines how focussed the glow effect is. A low eccentricity value will
create a concentrated glow with a fast decay. A high eccentricity value will
create a ball-like glow.
glow_eccentricity | 121
Comments:
The degree to which a glow effect will focus towards the center is limited. For
very low values( 0.01 ) the quality on page 130 parameter should be increased
for the best effect. Generally, however, it is best to use a glow with a low spread
value with a halo effect that is more spread out.
Example:
glow_eccentricity = .5
glow_opacity
Syntax:
glow_opacity = <scalar>
Range:
Any non-negative number
Default:
0.0
Purpose:
To allow a shader glow to obscure objects.
Comments:
Normally the shader glow is added on top of the light in the scene. If the
opacity is greater than zero, then the glow will be more opaque where it is
brightest. This is useful when simulating fire and smoke effects, which
frequently do not let all the light in a scene pass through. If you want the
glow to appear on the background only, and not obscure any objects, then
an opacity value of -1 will do this.
Example:
glow_opacity = .3
122 | Chapter 4 ENVIRONMENT Section
glow_radial_noise
Syntax:
glow_radial_noise = <scalar>
Range:
Any floating point number
Default:
0.0
Purpose:
To simulate starburst effects and eyelashes refracting light.
Comments:
Although this is similar to the radial noise effect on light glows, the effect will
be very blurry unless a small, pointlike source of shader glow is used.
Example:
glow_radial_noise = 0.5
glow_star_level
Syntax:
glow_star_level = <scalar>
Range:
Any floating point number
Default:
0.0
glow_radial_noise | 123
Purpose:
To simulate camera star filter effects.
Comments:
Although this is similar to the star_level effect on light glows, the effect will
be very blurry unless a small, pointlike source of shader glow is used.
Example:
glow_star_level = .6
glow_spread
Syntax:
glow_spread = <scalar>
Range:
Any non-negative number.
Default:
0.05
Purpose:
This determines how far light from the glow will spread out across the image.
Comments:
As the spread increased, the size of texture on the glow_color on page 120
increases as well.
Example:
glow_spread = .2
124 | Chapter 4 ENVIRONMENT Section
glow_type
Syntax:
glow_type = <constant>
Range:
<LINEAR_GLOW or SPECTRAL or RIM_HALO>
Default:
LINEAR_GLOW
Purpose:
To specify the falloff and coloration method for the glow effect.
Example:
glow_type = SPECTRAL
halo_color
Syntax:
halo_color = <color>
Range:
Any floating point values.
Default:
(100,100,100)
Purpose:
To set the color and brightness for the glow effect. To create very bright glows,
set the glow_color on page 120 high, for example(400,400,400). Setting the
glow brightness on the shader should be used to set only the brightness relative
glow_type | 125
to other shaders, whereas the halo_color should be used to set the overall
brightness of the glow effect.
Comments:
This parameter may be texture mapped (a circular or radial ramp texture is
particularly useful). If this texture mapped, then texture will appear around
glowing objects. The smaller the source of the glow, the more "focussed" the
image of the texture will appear. If the halo_eccentricity on page 126 parameter
is set to 1.0 then the full texture will be more visible.
Example:
halo_color = ( 300, 200, 100 )
halo_eccentricity
Syntax:
halo_eccentricity = <scalar>
Range:
Any non-negative number
Default:
0.1
Purpose:
This determines how focussed the glow effect is. A low eccentricity value will
create a concentrated glow with a fast decay. A high eccentricity value will
create a strong halo.
Comments:
The degree to which a glow effect will focus towards the center is limited. For
very low values(0.01) the quality on page 130 parameter should be increased
for the best effect. Generally, however, it is best to use a glow with a low spread
value with a halo effect that is more spread out.
126 | Chapter 4 ENVIRONMENT Section
Example:
halo_eccentricity = .5
halo_lens_flare
Syntax:
halo_lens_flare = scalar
Range:
any non-negative number
Default:
0.0
Purpose:
This simulates a bright glow bouncing off camera lenses.
Comments:
The effect is applied to the whole glow. To simulate a camera lens flare a small
glow source should be used and the halo eccentricity should be high. This
will create a set of fuzzy circles in a line through the center of the image.
Example:
halo_lens_flare = 0.5
halo_radial_noise
Syntax:
halo_radial_noise = <scalar>
Range:
Any floating point number
halo_lens_flare | 127
Default:
0.0
Purpose:
To simulate starburst effects and eyelashes refracting light.
Comments:
Although this is similar to the radial noise effect on light glows, the effect will
be very blurry unless a small, pointlike source of shader glow is used.
Example:
halo_radial_noise = 0.5
halo_spread
Syntax:
halo_spread = <scalar>
Range:
Any non-negative number.
Default:
0.3
Purpose:
This determines how far light from the halo will spread out across the image.
Comments:
As the spread increased, the size of texture on the halo_color on page 125
increases as well.
128 | Chapter 4 ENVIRONMENT Section
Example:
halo_spread = .2
halo_star_level
Syntax:
halo_star_level = <scalar>
Range:
Any floating point number
Default:
0.0
Purpose:
To simulate halo effects.
Comments:
Although this is similar to the star_level effect on light glows, the effect will
be very blurry unless a small, pointlike source of shader glow is used.
Example:
halo_star_level = .6
halo_type
Syntax:
halo_type = <constant>
Range:
<LINEAR_GLOW or SPECTRAL or RIM_HALO>
halo_star_level | 129
Default:
LINEAR_GLOW
Purpose:
To specify the falloff and coloration method for the halo effect.
Example:
glow_type = SPECTRAL
quality
Syntax:
quality = <scalar>
Range:
Non-negative
Default:
0.5
Purpose:
Raises the quality in order to properly calculate glow for very small objects
like twinkling stars. Very high values may be needed (around 50) for small
objects, especially when the glow and halo spreads are large.
shader_glow on page 120 is applied to a scaled-down sample of the image (for
best speed). When the glowing objects are small, the quality level should be
set high. For scenes where a large portion of the screen is glowing (for example,
when a glowing window fills the frame) then the quality should be set low in
order to avoid long rendering times.
When the image is rendered, the following lines appear if there is shader glow:
Glow Filter Width = 21
Glow Resolution = 0.638943
130 | Chapter 4 ENVIRONMENT Section
If the Glow Resolution is equal to 1.0, then the quality is as high as it can go
(the shader glow image is the same size as the output pix file). The quality
setting sets the Glow Resolution based on the Glow Filter Width so that render
time is roughly constant. This takes advantage of the fact that the blurry glows
(large filter size) generally do not require high resolution.
The time to calculate the shader glow generally goes up in proportion to
filter_width * filter_width * pix_size * pix_size * glowing pixels. (where pix
size = Glow_resolution * output_image_size and glowing_pixels is = pixels
with shaderglow divided by pixels without shaderglow.
Comments:
If the quality is very high large glowing objects can take a long time to render.
Example:
quality = 10.0
radial_noise_frequency
Syntax:
radial_noise_frequency = <scalar>
Range:
-infinity to infinity
Default:
0.5
Purpose:
To control the smoothness of the glow and fog radial noises.
Comments:
See glow_radial_noise on page 123.
radial_noise_frequency | 131
Example:
radial_noise_frequency = 3.0
star_points
Syntax:
star_points = <scalar>
Range:
0 to infinity
Default:
4.0
Purpose:
To set the number of points on star filters. (see glow_star_level on page 123.)
Comments:
Values of 1 and 2 are frequency useful. For example if star_points = 1.0 and
glow_star_level = 1.0 and the glow_type on page 125= RAINBOW, then a familiar
rainbow arch will be generated.
Example:
star_points = 5.0
threshold
Syntax:
threshold = <scalar>
Range:
0-1
132 | Chapter 4 ENVIRONMENT Section
Default:
0
Purpose:
This can be used so that only the brightest elements of shading glow. For
example, one can make specular highlights twinkle by using threshold. If the
threshold is .9, for example, then only the brightest portions of a glowing
object will glow.
Comments:
Sometimes it helps to lower the glow_intensity on the shader and greatly
increase the specular color (beyond 255) to insure that only the specular
highlight will glow.
Example:
threshold = .5
threshold | 133
134
Data Items
5
Creating Data Items
You will specify data items either literally or by defining and using variables.
Literal data items are used once and then discarded. Some data types cannot be
used literally (they must be assigned to variables).
Variables are defined in terms of literals, but can be referenced by name as many
times as needed.
Declaring Variables
Variables are defined and named in the DEFINITION section of the SDL file.
Keep the following in mind when using variables:
■
The order in which data items are defined is significant: you can only
reference data items that were defined previously in the text file.
■
You can define variables in terms of other variables and literal values.
■
Every variable must have a unique name (all variables exist in the same name
space).
■
You cannot define a variable more than once.
■
Once variables are defined, they persist until the end of the file.
■
Names of variables follow the same rules and use the same character set as
in the C language specification. Case is significant.
135
■
Each data type (with the exception of arrays, which collect other data
types) has a list of components that must be given values. If you do not
assign a value to a component, a default value will be used.
Specifying Literals
A literal usage and a variable definition are similar.
Keep the following in mind when using literals:
■
Literals are only meaningful when they are used. Afterwards they are
discarded. To use the same literal more than once, assign it to a variable.
■
A literal can contain variables and other literal values.
136 | Chapter 5 Data Items
Data types
6
SDL groups data into 23 formal types. Click on the highlighted text in the brief descriptions
below to see complete descriptions of the data types.
■
Array Data Type on page 139
A named group of data items (data items themselves do not have names). Arrays are created
with a fixed size. Items in the array are numbered from 0. Arrays can contain items of any
type (include other arrays). Arrays are often used to handle CVs.
■
Camera Data Type on page 140
Cameras are objects, similar to any piece of geometry: they are defined using a data type
and then instanced as an object. This allows multiple cameras, saving of cameras, and so
on.
■
This data type is equivalent to the old CAMERA section.
■
Curve Data Type on page 169
A series of control vertices (CVs) for a spline curve or surface. Patches, faces, and motion
curves are defined in terms of spline curves. Curves exist in 3D space (technically,
homogenous 4-space).
■
CV Data Type on page 172
A control vertex (CV) of a spline curve or surface. Curves are defined in terms of CVs. CVs
exist in 3D space (technically, homogenous 4-space).
■
Face Data Type on page 173
A planar object bounded by a curve, possibly with holes. Faces are a much more efficient
way of representing a planar area than a patch surface.
■
Filename Data Type on page 185
Can be used in place of literal filenames.
■
Light Data Type on page 186
Various types of light source.
■
Motion_curve Data Type on page 286
A curve used for animation, usually as a path to follow.
137
■
Parameter_curve Data Type on page 286
Similar to a normal curve, used for animate curves. Parameter curves exist in 2D space
and carry slope (tangent) information used for animation.
■
Parameter_vertex Data Type on page 288
Similar to a CV, used for animate curves. Parameter vertices exist in 2D space and carry
slope (tangent) information used for animation.
■
Patch Data Type on page 289
A spline surface defined by bounding CVs.
■
Polyset Data Type on page 314
A polygonal mesh. You can specify a polyset literally or as a named variable.
■
Scalar Data Type on page 330
A single numeric value. Scalars are stored and operated on as floating point, but will be
automatically converted when assigned to items that require an integer.
■
Shader Data Type on page 331
A shader description.
■
Texture Data Type on page 364
A mathematical function used to create textures for shaders.
■
Transformation Data Type on page 377
A set of matrices that relates the position, orientation and size of an object to the world
coordinate system. This datatype can be stored and assigned, but not examined or
operated on (it is an “opaque” data type).
■
Trim_vertex Data Type on page 383
Similar to a CV, used for trim curves. Trim vertices include extra information about their
relationship to the surface being trimmed.
■
Trim face Data Type on page 382
An ordered list of trim boundaries, defining a part of a NURBS surface to keep or discard
in a trim operation.
■
Trim boundary Data Type on page 377
An ordered list of trim edges, circling an area of a trimmed patch in parametric space.
■
Trim b-spline Data Type on page 378
A monotonic ordered list of trim curves, defining a 2D spline on a patch in parametric
space.
■
Trim curve vertex Data Type on page 380
An ordered list of 4 numbers representing the U, V, and T coordinates of a spline curve.
■
Trim edge Data Type on page 381
138 | Chapter 6 Data types
An ordered list of trim B-splines that describe an edge of a trim region on a NURBS
surface.
■
Triple Data Type on page 384
An ordered triplet of numeric values. Very useful for storing 3D coordinates, vectors,
and RGB values.
Array Data Type
Declaration:
array <name> [ <number of elements> ];
Reference:
<name> [ <number of desired element> ]
Purpose:
An array may only be specified as a variable (see Declaring Variables on page
135). It must have a name. Whereas other data types have component items,
each of a specific type and with defined semantics, an array is just an
aggregation of items. The elements of an array may be of any type, and their
meaning depends upon their contents.
Comments:
The syntax of an array reference is
<array name> [ <subscript> ]
where the <subscript> is any expression. The subscript will be converted to
an integer for purposes of referencing the array element.
Example:
array b[3];
Array Data Type | 139
Camera Data Type
Declaration:
camera <name> ( <component list> ) ;
Reference:
<name>fov
Literal:
camera ( <component list> )
Purpose:
This defines a camera. A camera is an object that may be defined as a literal
(see Specifying Literals on page 136) in the MODEL Section on page 37.
Similarly, a variable of type camera may be instanced (see Declaring Variables
on page 135). Each camera in the MODEL section (whether instanced or literal)
is capable of producing output independent of any other cameras. If a camera
is specified as a variable, it must have a name. Any of the following
components may be given between the parentheses:
■
active on page 144
■
aspect on page 144
■
aspect_ratio_pixel on page 145
■
auto_focus on page 146
■
depth_file on page 146
■
depth_of_field on page 147
■
far on page 148
■
filmaperture_x on page 148
■
filmaperture_y on page 149
■
filmoffset_x on page 150
■
filmoffset_y on page 150
■
focal_distance on page 151
140 | Chapter 6 Data types
■
focal_length on page 152
■
fov on page 152
■
f_stop on page 153
■
mask on page 154
■
matte_depth on page 156
■
matte_order on page 156
■
matte_plane on page 157
■
motion_blur on page 158
■
near on page 159
■
perspective on page 160
■
pix on page 160
■
placement_fit_code on page 162
■
placement_shift on page 163
■
scaling_factor on page 164
■
twist on page 164
■
units_to_feet on page 165
■
up on page 166
■
view on page 166
■
viewport on page 167
■
win_xsize on page 168
■
win_ysize on page 168
All components are specified using a keyword=value form. Components are
separated by commas. Not all components are optional. The components may
be specified in any order. Components that are not specified take on their
default value. If any component is specified more than once, the last such
specification will be used, and all previous ones ignored.
The camera’s location is (0, 0, 0). The location of the eye is the same as that
of the camera. The location of the camera corresponds to the apex of a pyramid
that encloses all of the objects which will be seen in the rendered image. These
Camera Data Type | 141
objects are projected on a window onto the world whose relative dimensions
are defined by the fov on page 152 and aspect on page 144 statements.
Orientation of the “viewing” pyramid is done by transforming the whole
camera in the scene using the normal mechanisms.
Aiming the camera is accomplished by transforming the camera like any other
object.
The name of the output file(s) created may be regarded as camera information
since each camera will necessarily output its own view of the scene. If more
than one camera (either literal or instance) is present in the MODEL section,
then the second one encountered and all subsequent ones must have a pix
on page 160 component or a mask on page 154 component (or both) specified
to define where the result of the rendering is to be output. If such a required
component is absent, then an error condition exists and the processing is
stopped with an error message. The first camera encountered must likewise
have a destination for its output. However, unlike subsequent ones, the first
camera has a default (the image goes to “stdout”, no mask is produced). It
may also be set by the DEFINITION Section on page 49parameters or by the
command line options. Note that if the first camera’s output is specified in
more than one of the 3 possible ways (command line, operation parameter,
camera component), then the command line specification will be used, if
given, and failing that, the camera component will be used. Specification of
camera output by use of DEFINITION parameters will only be used if no other
specification has been given.
NOTE Due to numerical precision problems, the camera’s motion is unstable if it
passes directly over the vertical pole and is looking straight down (the Y axis in
Y-UP systems, or the Z axis in Z-UP systems). To avoid this problem when animating
the camera, ensure that it is at least one degree off the pole
The aspect ratio, in the AliasStudio system, is a product of the pixel aspect
ratio and the image aspect ratio. The pixel aspect ratio is currently saved in
the field aspect_ratio_pixel on page 145. When using SGI equipment, numbers
are based on square pixels, which have a ratio of 1:1; hence, no additional
multiplication is required. The pixel aspect ratio may be different for other
machines. If you’re using such a machine, multiply the pixel aspect ratio times
the image aspect ratio as given, and edit the aspect ratio in SDL to reflect these
new numbers.
Table of Pixel Aspect Ratios
Pixel Aspect Ratio
142 | Chapter 6 Data types
Format
1:1
IRIS NTSC
1:1
IRIS PAL
4:3
Raster Tek's Hidef Frame Buffer
9:8
Abekas Internal Frame Buffer
4:3
Raster Tek's NTSC Frame Buffer
9 : 10
Quantel's Harry Interface
1:1
Full Frame 1K width
1:1
Motion Picture 1K with sound track
1:1
Motion Picture, no sound track
For example, if the aspect ratio part of the SDL Camera statement currently
reads
aspect = 320 / 240,
and you are using Quantel’s Harry Interface, edit it to read:
aspect = ((320 / 240) * (9/10)),
aspect_ratio_pixel = (9/10),
Example:
camera only_camera ( view
twist = -17.9;
fov = 35.0,
aspect = 320 / 240,
viewport = (0, 319, 0, 239),
near = 0.2
);
= (-2.1, -2.1, -2.1),
By default, AliasStudio creates a “pixel_aspect” variable in the DEFINITION
Section of SDL that allows you to quickly change the pixel aspect ratio should
you need to. Then the below statement should be in the camera description
Camera Data Type | 143
aspect_ratio_pixel = pixel_aspect,
active
Syntax:
active = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Purpose:
A Boolean flag that controls whether the camera will be used or not.
Comments:
This component may be animated.
Example:
active = FALSE
aspect
Syntax:
aspect = <scalar>
Range:
>0
Default:
1.0
144 | Chapter 6 Data types
Purpose:
This defines the ratio of the x and y dimensions of the window of the world.
All visible objects are projected onto this window. In order for objects not to
be distorted, the aspect ratio of the physical rectangle on the screen defined
by the viewport on page 167 statement must be the same as the value for aspect.
Some output devices do not have square pixels. In order to create undistorted
images, the following formula provides the correct aspect ratio: ( vp width /
vp height ) * ( pixel width / pixel height ) where “vp” means viewport.
Starting version 7, the definition of aspect has changed slightly. It just indicates
the pixel aspect ratio. The viewport is no longer a needed consideration because
it is computed on-the-fly in version 7.
Comments:
This component may be animated.
Example:
aspect = ((xright – xleft) / (yhigh – ylow))
This example uses an expression made up of system defined variables. It is
appropriate for an image that will be output to a device that has square pixels.
aspect_ratio_pixel
Syntax:
aspect_ratio_pixel = <scalar>
Range:
>0
Default:
1.0
Purpose:
This defines the pixel aspect ratio appropriate for different output devices.
Camera Data Type | 145
Comments:
This component may be animated.
Example:
aspect_ratio_pixel = 1.0
This example is appropriate for an image that will be output to a device that
has square pixels.
auto_focus
Syntax:
auto_focus= <scalar>
Range:
0 (FALSE) or 1 (TRUE)
Default:
FALSE
Purpose:
This is relevant when depth of field is turned on. If auto_focus is turned on,
then the focus point is the lookat point of the camera. If auto_focus is turned
off, then the focal_distance on page 151 is used to determine the focus point.
Comments:
This component may be animated.
Example:
auto_focus = FALSE
depth_file
Syntax:
depth_file = <filename>
146 | Chapter 6 Data types
Purpose:
This defines the filename used as output for a floating point depth value for
each pixel, instead of a color or mask value.
For users who want to read the file, or write utilities that make use of the file,
the format is as follows:
1 integer (the file's magic number) should be 55655
1 short (the image width, or X dimension)
1 short (the image height, or Y dimension)
X * Y floats (representing the pixels)
To use the results as an 8-bit texture file, see depthmap in the Standalone
Utilities manual.
depth_of_field
Syntax:
depth_of_field = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
FALSE
Purpose:
This specifies that depth of field will be used when RayTracing. Most renderers
in the world mimic a pin hole camera, which has an infinite depth of field.
RayTracing allows the use of real depth of field, simply and easily. Only the
distance of focus in the scene, and the focal_length on page 152 and f_stop on
page 153 of the lens have to be specified.
Comments:
This component may be animated. You must specify focal_distance on page
151 if depth_of_field is TRUE.
Camera Data Type | 147
Example:
depth_of_field = TRUE
far
Syntax:
far = <scalar>
Range:
Any positive floating point number greater than the value assigned to near
on page 159.
Default:
1000
Purpose:
This sets the position of the far plane. Objects are not clipped to the far plane.
However, calculations for Fog on page 412use the far value to compute the
distance from the camera to the background. Objects in the scene that are
further than the clipping plane will not render correctly.
Comments:
This component may be animated.
Example:
far = 50.0
filmaperture_x
Syntax:
filmaperture_x = <scalar>
Range:
Any positive floating point number greater than 0.
148 | Chapter 6 Data types
Default:
1
Purpose:
This sets the aperture width in the horizontal direction. Another term for
aperture in camera terminology is film back.
Comments:
This component is only relevant for perspective cameras. The region outside
of that defined by the filmaperture and filmoffset will be rendered in black.
Example:
filmaperture_x = 1.0
filmaperture_y
Syntax:
filmaperture_y = <scalar>
Range:
Any positive floating point number greater than 0.
Default:
1
Purpose:
This sets the aperture width in the vertical direction. Another term for aperture
in camera terminology is film back.
Comments:
This component is only relevant for perspective cameras. The region outside
of that defined by the filmaperture and filmoffset will be rendered in black.
Camera Data Type | 149
Example:
filmaperture_y = 1.0
filmoffset_x
Syntax:
filmoffset_x = <scalar>
Range:
Any floating point number less than half of filmaperture_x.
Default:
0
Purpose:
This sets the film offset in the horizontal direction.
Comments:
This component is only relevant with perspective cameras. The region outside
of that defined by the filmaperture and filmoffset will be rendered in black.
Example:
filmoffset_x = 0.0
filmoffset_y
Syntax:
filmoffset_y = <scalar>
Range:
Any floating point number less than half of filmaperture_y.
Default:
0
150 | Chapter 6 Data types
Purpose:
This sets the film offset in the horizontal direction.
Comments:
This component is only relevant with perspective cameras. The region outside
of that defined by the filmaperture and filmoffset will be rendered in black.
Example:
filmoffset_y = 0.0
focal_distance
Syntax:
focal_distance = <scalar>
Range:
Non-negative.
Default:
none
Purpose:
The focal distance is the distance from the camera (lens) to a point in the
scene upon which the lens is focused. The value specified is interpreted as
being in units of feet to agree with depth of field charts in published guides.
Comments:
This must be specified if depth_of_field on page 147 is true.
This component may be animated.
Example:
focal_distance = 15.0
Camera Data Type | 151
focal_length
Syntax:
focal_length = <scalar>
Range:
Greater than 1
Default:
35
Purpose:
The focal length of the lens is a property of the lens. The value specified is
interpreted as being in units of millimeters.
Comments:
This component may be animated.
Example:
focal_length = 50.0
fov
Syntax:
fov = <scalar>
Range:
0.2 to 179.
Default:
45
152 | Chapter 6 Data types
Purpose:
This statement sets the camera’s field of view in degrees. A setting of 40
approximates a 35mm lens, and 20 is a 50mm lens. Note that for very wide
angles, the distortions are not those of an actual wide-angle optical lens. A
value outside the above range will generate a run time error message.
Starting in version 6.0 of SDL, instead of specifying the field of view with fov
on page 152, it is possible to specify it using aov, which stands for angle of
view (this is the more classical camera terminology). Both are identical in
definition. Furthermore, if the SDL file states that it is a version 6.0 file (or
greater), the fov will be interpreted as cropping in the vertical direction, rather
than the previously cropped horizontal direction.
Comments:
This component may be animated.
Example:
fov = 20
f_stop
Syntax:
f_stop = <scalar>
Range:
Non-negative.
Default:
8
Purpose:
Any good photography reference guide will contain a depth of field table
giving focal distances based on focal length and f stop. You may then choose
whichever focal_length on page 152 / f stop combination produces the desired
result, and render the image. The same reference manual will also have a
section for calculating f stop and focal length directly from the focal_distance
on page 151, fov on page 152 and aspect on page 144 ratio.
Camera Data Type | 153
Comments:
This component may be animated.
Example:
f_stop = 5.6
mask
Syntax:
mask = <filename>
Default:
Special — see the comments.
Purpose:
To define the output destination of the mask file produced by this camera.
Comments:
Each camera in the MODEL section (whether instanced or literal) is capable
of producing output independent of any other cameras. The output may be
an image file, a mask file or both. If this (mask) component is specified, then
a mask output is produced. If it is omitted, then no mask is created for this
camera. A similar situation exists for the pix component. If both the pix on
page 160 and the mask components are absent, then either a default is used or
an error occurs, depending upon the circumstances described below.
If more than one camera (either literal or instance) is present in the MODEL
section, then the second one encountered and all subsequent ones must have
a pix component or a mask component (or both) specified to define where
the result of the rendering is to be output. If such a required component is
absent, then an error condition exists and the processing is stopped with an
error message. The first camera encountered must likewise have a destination
for its output. However, unlike subsequent ones, the first camera has a default
(an image is produced and goes to “stdout”, no mask is produced). It may also
be set by the DEFINITION parameters or by the command line options. Note
that if the first camera’s output is specified in more than one of the 3 possible
ways (command line, operation parameter, camera component), then the
command line specification will be used, if given, and failing that, the camera
154 | Chapter 6 Data types
component will be used. Specification of camera output by use of DEFINITION
parameters will only be used if no other specification has been given.
Only the first camera may have its output specified by default, or by the
command line or by an DEFINITION parameter. All other cameras must have
either the pix component or the mask component (or possibly, but not
necessarily, both) specified.
The actual name of an output file produced by a camera (either PIX or MASK
or both) may be different from what is specified by the user. The name used
is comprised of four parts:
■
specified
■
stereo
■
animation
■
field
The first, or specified part, is exactly what was specified by the user (which
may or may not have an extension. Refer to the section on filenames for more
information).
The second, or stereo part, is only used when rendering stereo images. When
stereo = TRUE either “_left” or “_right” will be appended to the name
appropriately.
The third, or animation part, is used only when rendering an animation (that
is, when animation = TRUE). A further “dot” extension is appended to the
name. (This is not to be confused with a user specified extension.)
This will be a non-negative integer prefixed by a single period (“dot”). Its value
will be equal to startextension for the first frame and will increment by the
value of byextension for each subsequent frame produced. Refer to the
descriptions on startextension on page 84 and byextension on page 57 in the
Definition section of this manual for more information.
The fourth, or fields portion is only produced when rendering on fields (that
is, when fields on page 64 = TRUE). The single character “e” is appended to
the names of all files produced for an “EVEN” field, and the single character
“o” is appended for “ODD” ones.
Comments:
This component may be animated.
Camera Data Type | 155
Example:
mask = ("~/mask/thisone")
matte_depth
Syntax:
matte_depth= <scalar>
Range:
-infinity to infinity
Default:
Purpose:
Specifies a distance in units from the eye point. Thus, positive values indicate
that the matte plane is behind the camera — we recommend this be used only
when you are raytracing reflections that are behind the camera. Note that the
matte_plane on page 157 description must precede the matte_depth and
matte_order on page 156 descriptions.
NOTE Note: Specify either matte_depth or matte_order, not both.
Example:
matte_depth = -10.0
matte_order
Syntax:
matte_order= <scalar>
Range:
-infinity to infinity
156 | Chapter 6 Data types
Default:
Purpose:
Specifies a distance in units from the eye point. A positive value indicate that
the matte_plane on page 157 is behind the entire geometry database, and a
negative value indicate that the matte-plane is in front of the database. Larger
values determine the front-ordering of these matte-planes. Note that the
matte_plane description must precede the matte_depth on page 156 and
matte_order descriptions.
NOTE A matte_order value of 0 indicates NO ordering. This means that it resides
exactly at the back of any rendering (sort of like a backdrop).
NOTE Specify either matte_depth or matte_order, not both.
Example:
matte_order = -0.500000
matte_plane
Syntax:
matte_plane= <texture>
Range:
Default:
Purpose:
Specifies the name of a file texture to be used as a matte plane.
At the moment, only file textures (like “file” and “stencil”) are being handled
in matte-planes in the interactive package. In the Scene Description Language,
other texture-types can be applied to matte-planes.
Camera Data Type | 157
Example:
texture back (
procedure = Stencil,
mask_level = 1.0,
mask_blur = 0.0,
edge_blend = 0.0,
positive_key = OFF,
image_file = "/usr/u/myname/user_data/demo/pix/back.pix.1",
key_masking = ON,
color_key = (1.000000, 1.000000, 1.000000),
hue_range = 0.500000,
sat_range = 0.500000,
val_range = 0.500000,
threshold = 0.500000,
active = TRUE,
rgbmult = (1.000000, 1.000000, 1.000000),
rgboffset = (0.000000, 0.000000, 0.000000),
ucoverage = 1.000000,
vcoverage = 1.000000,
utranslate = 0.000000,
vtranslate = 0.000000,
uwrap = TRUE,
vwrap = FALSE,
urepeat = 320.000000 / 321.000000,
vrepeat = 241.000000 / 241.000000,
uoffset = 50.000000 / 321.000000,
voffset = 0.000000 / 241.000000
);
This is an example of using a matte-plane with the filename "back.pix.1" and
chroma-keying specified. If no chroma-keying or matte-files are specified,
then the "file" texture is used instead.
motion_blur
Syntax:
motion_blur = <scalar>
Default:
ON
158 | Chapter 6 Data types
Range:
0 (OFF) or non-zero (ON)
Purpose:
If motion_blur is turned on for the file, this flag indicates that motion blur
should be calculated for this object.
Example:
motion_blur = ON
near
Syntax:
near = <scalar>
Range:
Unexpected results may be produced when near is assigned a very small value.
Therefore, the recommended minimum setting is 0.1. The number must be
greater than 0.
Default:
0.2
Purpose:
This sets the position of the near clipping plane. It truncates the pyramid of
vision when objects come too close to the apex. Interior sectional views of
objects are attained by setting the near plane within the objects.
Comments:
This component may be animated.
Example:
near = 1.0
Camera Data Type | 159
perspective
Syntax:
perspectivet = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Purpose:
A Boolean flag that controls the projection scheme. The camera uses perspective
projection if the flag is TRUE; otherwise, it uses orthographic projection.
Comments:
If perspective = FALSE, win_xsize on page 168 and win_ysize on page 168 must
be specified.
Example:
perspective = FALSE
pix
Syntax:
pix = <filename>
Default:
Special — see the comments.
Purpose:
Defines the destination of the image file produced by the camera.
160 | Chapter 6 Data types
Comments:
Each camera in the MODEL section (whether instanced or literal) is capable
of producing output independent of any other camera. The output may be
an image file, a mask file or both. If this (pix) component is specified, then
an image output is produced. If it is omitted, then no image is created for this
camera. A similar situation exists for the mask component. If both the pix
and the mask on page 154 components are absent, then either a default is used
or an error occurs, depending upon the circumstances given below.
If more than one camera (either literal or instance) is present in the MODEL
Section on page 37, then the second one encountered and all subsequent ones
must have a pix component or a mask component (or both) specified to define
where the result of the rendering is to be output. If such a required component
is absent, then an error condition exists and the processing is stopped with
an error message. The first camera encountered must likewise have a
destination for its output.
However, unlike subsequent ones, the first camera has a default (an image is
produced and goes to “stdout”, no mask is produced). It may also be set by
the DEFINITION Section on page 49 parameters or by the command line
options. Note that if the first camera’s output is specified in more than one
of the 3 possible ways (command line, operation parameter, camera
component), then the command line specification will be used, if given, and
failing that, the camera component will be used. Specification of camera
output by use of DEFINITION parameters will only be used if no other
specification has been given.
Only the first camera may have its output specified by default, or by the
command line or by an DEFINITION parameter. All other cameras must have
either the pix component or the mask component (or possibly, but not
necessarily, both) specified.
The actual name of an output file produced by a camera (either PIX or MASK
or both) may be different from what is specified by the user. The name used
is comprised of four parts:
■
specified
■
stereo
■
animation
■
field
Camera Data Type | 161
The first, or specified part, is exactly what was specified by the user (which
may or may not have an extension. Refer to the section on filenames for more
information).
The second, or stereo part, is only used when rendering stereo images. When
stereo = TRUE either “_left” or “_right” will be appended to the name
appropriately.
The third, or animation part, is used only when rendering an animation (that
is, when animation = TRUE). A further “dot” extension is appended to the
name. (This is not to be confused with a user-specified extension.)
This will be a non-negative integer prefixed by a single period (“dot”). Its value
will be equal to STARTEXTENSION for the first frame and will increment by
the value of BYEXTENSION for each subsequent frame produced. Refer to the
descriptions on startextension on page 84 and byextension on page 57 in the
Definition section of this manual for more information.
The fourth, or fields portion is only produced when rendering on fields (that
is, fields on page 64 = TRUE). The single character “e” is appended to the
names of all files produced for an “EVEN” field, and the single character “o”
is appended for “ODD” ones.
Comments:
This component may be animated.
Example:
pix = ("~/pix/thatone")
placement_fit_code
Syntax:
placement_fit_code = <scalar>
Range:
0, 2
Default:
0.0
162 | Chapter 6 Data types
Purpose:
Placement_fit_code is only relevant when the aspect ratio of the filmback does
not match the aspect on page 144 ratio of the rendering resolution. If there is
a mismatch in aspect ratios, then there will be some clipped out regions in
the resultant rendering. There are three variations in clipping out regions:
■
0: best fit in both vertical and horizontal direction.
■
1: fit in the horizontal direction, and clipped in the vertical direction.
■
2: fit in the vertical direction, and clipped in the horizontal direction.
Example:
placement_fit_code = 0.0
placement_shift
Syntax:
placement_shift = <scalar>
Range:
-1, 1
Default:
0.0
Purpose:
Placement_shift is only relevant when the aspect ratio of the film back does
not match the aspect on page 144 ratio of the rendering resolution. If there is
a mismatch in aspect ratios, there will be some clipped out regions in the
resultant rendering, as described above. When placement_shift is set to 0, the
image will be centered so that the clipped out regions will be equally divided
on both ends. If set to -1, then the image is shifted to the right (or to the top),
where one end of the clipped out region becomes totally visible. A setting of
1 has a similar effect, but in the opposite direction.
Camera Data Type | 163
Example:
placement_shift = 0.0
scaling_factor
Syntax:
scaling_factor= <scalar>
Range:
>0
Default:
1.0
Purpose:
Scaling_factor is only relevant to depth_of_field on page 147. This provides for
a better control of the fuzzy effects from depth of field. The larger the
scaling_factor, the more amplified the depth of field’s fuzzy effects.
Example:
scaling_factor = 1.0
twist
Syntax:
twist = <scalar>
Range:
unlimited
Default:
0.0
164 | Chapter 6 Data types
Purpose:
The twist sets the degrees of tilt away from the camera’s vertical axis. Tilting
the camera clockwise with a positive twist setting makes the world look like
it is tilted to the left.
Comments:
This component may be animated. twist is ignored if up on page 166 is specified.
Example:
twist = (animate( roll, frame ))
units_to_feet
Syntax:
units_to_feet = <scalar>
Range:
greater than 0.0
Default:
0.0
Purpose:
units_to_feet allows the definition of focal_distance on page 151 in units other
than feet (for example, in meters). The value of units_to_feet is the length of
the unit as expressed in terms of feet. In case of focal distance defined in
meters, units_to_feet will be 0.3048 since 0.3048 meters equals one foot.
Comments:
This component may be animated.
Example:
units_to_feet = 1.0
Camera Data Type | 165
up
Syntax:
up = <triple>
Range:
unlimited
Default:
0.0, 1.0, 0.0
Purpose:
The up vector is used as a reference to define the angle of twist, and is one of
the components affecting the orientation of the camera.
Comments:
This component may be animated. twist on page 164 is ignored if up is specified.
Example:
up = (animate( roll, frame ))
view
Syntax:
view = <triple>
Range:
There are no limits to value; however, if 0.0 or very large numbers are used
(for example, 10000000), unpredictable behavior may occur.
Default:
Not applicable — see below.
166 | Chapter 6 Data types
Purpose:
This describes the location in space, in absolute world coordinates, toward
which the camera is directed. The three components of the triple correspond
to the x, y and z coordinates, respectively. To always look at the same point,
use this statement. If not specified, the camera simply looks down the axis of
the viewing pyramid ( 0, 0, -1 relative to the camera) and is controlled by
transforming the camera as a whole.
Comments:
This component may be animated.
Example:
view = some_trip_var_name
viewport
Syntax:
viewport = ( <scalar> , <scalar> , <scalar> , <scalar> )
Range:
unbounded
Default:
(0, 644, 0, 485)
Purpose:
This statement maps, in pixels, the window of the world onto the screen. The
first two numbers set the beginning and the end of the horizontal coordinates.
The second two numbers set the beginning and the end of the vertical
coordinates. Note that this is the mapping of the viewing frustrum, and it
does not affect the area to be rendered as defined in the DEFINITION Section
on page 49. The origin of the screen is the lower left hand corner.
Comments:
Starting version 7, the viewport information will be ignored. A viewport is
automatically computed based on the information of the film back, film offset,
Camera Data Type | 167
etc. If a viewport was used for partial image rendering, this is now easily
specifiable in the interactive package without having to tweak with numbers.
Example:
viewport = (0, 319, 0, 239)
win_xsize
Syntax:
win_xsizet = <scalar>
Range:
unbounded
Default:
Not applicable - see below.
Purpose:
win_xsize defines the horizontal window size for orthographic rendering. The
unit of measure is the unit of measure used for the grid in the AliasStudio
system; by default, centimeters.
Comments:
This component works only when perspective on page 160 = FALSE.
Example:
win_xsize = 18.948872
win_ysize
Syntax:
win_ysizet = <scalar>
Range:
unbounded
168 | Chapter 6 Data types
Default:
Not applicable - see below.
Purpose:
win_ysize defines the vertical window size for orthographic rendering. The
unit of measure is the unit of measure used for the grid in the AliasStudio
system; by default, centimeters.
Comments:
This component works only when perspective on page 160 = FALSE.
Example:
win_ysize = 13.462891
Curve Data Type
Declaration:
curve <name> ( <component list> );
Reference:
<name>
Literal:
curve ( <component list> )
Purpose:
A curve is a non-uniform rational b-spline. It may be instanced as an object
in the MODEL Section on page 37. A curve may be specified as a literal or as
a variable. If specified as a variable, it must have a name. The following
components must be specified between the parentheses:
■
cvs on page 170
■
degree on page 171
Curve Data Type | 169
knots on page 171
■
All components are specified using a keyword=value form, and are separated
by commas. The components may be specified in any order.
Example:
curve curve#2 (
degree = 3,
knots = (
0.0
1.0
),
cvs = (
cv( ( -0.50656,
cv( ( -0.50998,
cv( ( -0.44153,
cv( ( -0.29094,
);
,
0.0
-0.43168,
-0.5717 ,
-0.62975,
-0.62975,
,
0.0
0.0
0.0
0.0
0.0
,
),
),
),
),
1.0
1.0
1.0
1.0
1.0
,
1.0 ,
),
),
),
) )
cvs
Syntax:
cvs = ( ( <cv>, <cv>, … <cv> ),
( <cv>, <cv>, … <cv> ),
.
.
.
( <cv>, <cv>, … <cv> ) )
Range:
Any collection of valid cvs (i.e., see the CV Data Type on page 172).
Default:
None. Must be specified.
Purpose:
This defines the control vertices for the curve.
170 | Chapter 6 Data types
Example:
cvs = (
cv( ( -0.50656,
cv( ( -0.50998,
cv( ( -0.44153,
cv( ( -0.29094,
);
-0.43168,
-0.5717 ,
-0.62975,
-0.62975,
0.0
0.0
0.0
0.0
),
),
),
),
1.0
1.0
1.0
1.0
),
),
),
) )
degree
Syntax:
degree = <scalar>
Range:
1 to 33
Default:
none
Purpose:
To describe the degree of the NURBS curve. To define a syntactically correct
curve, there must be at least degree + 1 control vertices.
Comments:
As the degree of the surface increases, it is a good idea to increase the rendering
subdivisions for the object defined with that curve.
Example:
degree = 3
knots
Syntax:
knots = ( <scalar>, <scalar>, …<scalar> )
Curve Data Type | 171
Range:
Each entry must evaluate to a real number, which must be greater than or
equal to the value of its predecessor.
Default:
None. Must be specified.
Purpose:
This defines the knot vector in the curve’s direction. It must match with
number of CVs given.
Comments:
It may be animated.
Example:
knots = ( 0, 1, 2, 3, 4, 5 )
CV Data Type
Declaration:
cv <name> ( <triple>, <scalar> ) ;
Reference:
<name>
Literal:
cv ( <triple>, <scalar> )
Purpose:
This defines a cv. A cv may be specified as a literal or as a variable. If specified
as a variable, it must have a name. All of its components are identified by
position rather than by keywords. They are interpreted as
( (x, y, z), w )
172 | Chapter 6 Data types
x, y, and z, are the coordinates of the cv; w is its weight.
Example:
cv
cv
cv
cv
u0
u1
u3
u3
((-1,
(( 0,
(( 1,
(( 2,
0,
0,
0,
0,
0),
0),
0),
0),
1);
1);
1);
1);
Face Data Type
Declaration:
face <name> ( <component list> ) ;
Reference:
<name>
Literal:
face ( <component list> )
Purpose:
A face is an object that may be instanced in the MODEL section. It defines a
planar surface whose boundary is given by a spline curve.
Comments:
A face may be specified as a literal or as a variable. If specified as a variable, it
must have a name. Any of the following components may be specified between
the parentheses:
■
active on page 175
■
boundaries on page 175
■
casts_shadow on page 176
■
clusters on page 177
■
cvs on page 178
Face Data Type | 173
■
degree on page 179
■
divisions on page 180
■
knots on page 180
■
light_list on page 181
■
motion_blur on page 182
■
motion_blur_shading_samples on page 182
■
motion_blur_texture_sample_level on page 183
■
particle_collisions on page 183
■
shader on page 184
All components are specified using a keyword=value form. Components are
separated by commas. The components may be specified in any order.
Components that are not specified take on their default value. If any
component is specified more than once, the last such specification will be
used, and all previous ones ignored.
Example:
face node7 (active = TRUE, divisions = 4,
shader = (DefaultShader ),
casts_shadow = TRUE,
boundaries = (
(degree = 3,
knots = (-0.4375
, -0.21875 , 0.0
, 1.0
, 2.0 ,
2.21875 , 2.4375
, 2.65625 , 3.65625 , 4.65625
),
cvs = ( cv(( -1.0839422,
0.0
, -1.8821912),
0.9999998),
cv(( -1.3428757,
0.0
,
0.220685 ),
1.0 ),
cv(( -0.2771195,
0.0
,
0.9785176),
0.9999996),
cv(( 1.1370566,
0.0
,
0.725904 ),
0.9999998),
cv(( 0.7208539,
0.0
, -1.9337564),
1.0000001),
cv(( -1.0839422,
0.0
, -1.8821912),
0.9999998),
cv(( -1.3428757,
0.0
,
0.220685 ),
1.0 ),
cv(( -0.2771195,
0.0
,
0.9785176),
0.9999996)
)
)
));
174 | Chapter 6 Data types
active
Syntax:
active = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Purpose:
A Boolean flag that controls whether the face is visible or not.
Comments:
This component may be animated. This is provided so the user can cause an
object to suddenly appear or disappear in an animation.
Example:
active = TRUE
boundaries
Syntax:
boundaries = (degree = <scalar>, knots = (....), ( <boundary description> ),
( <boundary description> ),
.
.
.
( <boundary description> ) )
Default:
none.
Face Data Type | 175
Purpose:
This defines the shape of the face, including the outer face and all inner faces.
Comments:
The definition consists of a list of curves. The first curve in the list is considered
the outer face—all subsequent curves are considered inner faces. Each curve
specified has its own set of 3 components: cvs on page 178, to define the curve
according to its polynomial basis; knots on page 180, to define the polynomial
basis; and divisions on page 180, to define the quality of the rendering
approximation. These components are discussed separately below. The
boundaries component must be specified, and it must contain at least one
curve. There may be any number of additional curves. Each curve in the list
(even if there is only one) must be enclosed within parentheses, and the list
itself must also be enclosed within parentheses. The boundaries component
may not be animated.
Example:
boundaries = (
(degree = 3,
knots = (-0.4375
, -0.21875 , 0.0
, 1.0
, 2.0 ,
2.21875 , 2.4375
, 2.65625 , 3.65625 , 4.65625
),
cvs = ( cv(( -4.4072771,
0.0
, -7.6529346),
0.9999998),
cv(( -5.4600935,
0.0
,
0.897299 ),
1.0 ),
cv(( -1.1267598,
0.0
,
3.9786241),
0.9999996),
cv(( 4.623239 ,
0.0
,
2.9515047),
0.9999998),
cv(( 2.9309711,
0.0
, -7.8625975),
1.0000001),
cv(( -4.4072771,
0.0
, -7.6529346),
0.9999998),
cv(( -5.4600935,
0.0
,
0.897299 ),
1.0 ),
cv(( -1.1267598,
0.0
,
3.9786241),
0.9999996)
)
)
casts_shadow
Syntax:
casts_shadow = <scalar>
176 | Chapter 6 Data types
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Purpose:
A Boolean flag that controls whether or not this face will cast a shadow.
Comments:
This component may be animated. Note that a transparent or semitransparent
object will not cast a shadow when RayCasting.
Example:
casts_shadow = FALSE
clusters
Syntax:
clusters = (<cluster matrix list>),
Range:
N/A
Default:
None.
Purpose:
A list of cluster matrices that affect the current surface.
Comments:
A cluster matrix describes the initial position of the matrix (4X4 scalars), the
type of cluster effect (JOINT or LEAF), JOINT level (or 0 if the type is LEAF),
and translate, rotate, scale as 3 scalar tuples.
Face Data Type | 177
Example:
clusters = (
clm( CL_r_peak,
1.0
, 0.0
, 0.0
,
0.0
, 1.0
, 0.0
,
0.0
, 0.0
, 1.0
,
0.283681 , 0.0285822, -0.5841172,
LEAF, 0,
0.0
, 0.0
, 0.0
,
0.0
, 0.0
, 0.0
,
1.0
, 1.0
, 1.0
),
clm( CL_knot45_section0_Rwrist,
1.0
, 0.0
, 0.0
,
0.0
, 1.0
, 0.0
,
0.0
, 0.0
, 1.0
,
0.283681 , 0.0285822, -0.5841172,
LEAF, 0,
0.0
, 0.0
, 0.0
,
0.0
, 0.0
, 0.0
,
1.0
, 1.0
, 1.0
)
clm( CL_cluster#10,
1.0
, 0.0
, 0.0
,
0.0
, 1.0
, 0.0
,
0.0
, 0.0
, 1.0
,
0.283681 , 0.0285822, -0.5841172,
JOINT, 3,
-0.2398842, -0.0303474, 0.0
,
0.0
, 0.0
, 0.0
,
1.0
, 1.0
, 1.0
)
cvs
Syntax:
cvs = ( <cv>, <cv>, … <cv> )
Default:
None. Must be specified.
178 | Chapter 6 Data types
0.0
0.0
0.0
1.0
,
,
,
,
0.0
0.0
0.0
1.0
,
,
,
,
0.0
0.0
0.0
1.0
,
,
,
,
),
Purpose:
Defines the control vertices for a face boundary curve.
Comments:
It may be animated.
Example:
cvs= ( cv(( 1,6,0),1),
cv((12,6,0),1),
cv((12,1,0),1),
cv(( 1,1,0),1)
),
degree
Syntax:
degree = <integer>
Range:
Greater than 0.
Default:
Required: no default
Purpose:
This defines the order of the NURBS curve in the u direction. 1 is a linear
curve, 3 is a cubic, and so on.
Comments:
This component may not be animated.
Example:
degree = 3
Face Data Type | 179
divisions
Syntax:
divisions = <scalar>
Range:
The minimum value is 1.
Default:
None. Must be specified.
Purpose:
This defines the smoothness of the contour along the face boundary curve.
Comments:
This component may be animated. Note that face boundary curves are always
subdivided using the uniform algorithm.
Example:
divisions = 8
knots
Syntax:
knots = ( <scalar>, <scalar>, …<scalar> )
Default:
None. Must be specified.
Purpose:
This specifies the knot vector for a face boundary curve. It must match with
the cvs on page 178 given.
180 | Chapter 6 Data types
Comments:
The individual values may be animated, but the number of items in the list
must not change.
Example:
knots = ( 0, 1, 2, 3, 4, 5 )
light_list
Syntax:
light_list = ( <light>, <light>, … <light> )
Range:
Each light given must have been defined; literals may not be used.
Default:
See the following.
Purpose:
Each item referenced must be the name of a previously declared light data
item (see Light Data Type on page 186), or an array element of type light.
Literals may not be used. This lists the lights to be used by this patch. If
light_list is omitted or if it is specified and is empty, all nonexclusive lights
will be used to illuminate the patch. If light_list is specified, and the list
contains defined lights, then all instances of those lights in the scene, and
only those, will be used for this patch. This enables situations where the user
may want 10 lights on a particular object, for example, but only two lights
on the rest of the scene.
Comments:
It may not be animated.
Example:
light_list = ( spot01, spot02, flood, globallight )
Face Data Type | 181
motion_blur
Syntax:
motion_blur = <scalar>
Default:
ON
Range:
0 (OFF) or non-zero (ON)
Purpose:
If motion_blur is turned on for the file, this flag indicates that motion blur
should be calculated for this object.
Example:
motion_blur = ON
motion_blur_shading_samples
Syntax:
motion_blur_shading_samples = <scalar>
Default:
3 - for bump or displacement mapped objects
1 - for all other objects
Range:
>= 3 for bump or displacement mapped objects
> 0 for all other objects
Purpose:
If motion_blur on page 158 is turned on for the file, this flag indicates the
number of samples done for shading of motion-blurred objects.
182 | Chapter 6 Data types
Example:
motion_blur_shading_samples = 1
motion_blur_texture_sample_level
Syntax:
motion_blur_texture_sample_level = <scalar>
Default:
3
Range:
0-5
Purpose:
If motion_blur on page 158 is turned on for the file, this flag indicates the level
of sampling done for texturing of motion-blurred objects. A 0 indicates no
extra samples (lowest quality) and 5 means highest quality motion-blurred
textures. Note, this flag does not apply to bump or displacement mapping.
Example:
motion_blur_texture_samples = 3
particle_collisions
Syntax:
particle_collisions = BOUNDING_BOX_COLLISIONS | OFF |
GEOMETRY_COLLISIONS
Range:
As above
Default:
OFF
Face Data Type | 183
Purpose:
To define which objects collide with particles.
Example:
particle_collisions = BOUNDING_BOX_COLLISIONS
shader
Syntax:
shader =( <shader>)
or
shading = ( <shader>, <shader>, …
<shader> )
Range:
The shaders given may be variables or array elements of type shader (see Shader
Data Type on page 331). Note that there is no such thing as a literal shader.
Default:
None. Must be specified.
Purpose:
This specifies which shading characteristics are assigned to the face.
Comments:
This component may be animated. If a list of shaders is specified, they will
be visible in the order given.
Example:
shader = ( label_1, bottle_1 )
184 | Chapter 6 Data types
Filename Data Type
Declaration:
filename <name> (“quoted string” <scalar> );
or
filename <name> (“quoted string”);
Reference:
<name>
Literal:
(“quoted string” <scalar> )
or
(“quoted string”)
Purpose:
This defines a filename. A filename may be specified as a literal or as a variable.
If specified as a variable, it must have a name. A filename has at least one, and
optionally two components. These are identified by position rather than by
keyword. The first component is a UNIX path. If only the first component is
present, then the path must specify a file. The second component is an
extension. If it is specified, then its value is converted to an integer and
appended (using the normal “dot” extension form) to the path. If an extension
component is supplied, then it will always be used. This does NOT depend
upon any sense of Animation.
The total filename (path plus extension) must identify a file.
A filename may specify a full or relative UNIX path. Relative paths are applied
with respect to the current working directory when the renderer is invoked.
A filename variable may receive either form (single component or two
component) in an assignment.
Example:
filename anim_texture_in(“~/texture/hoops” (frame -1));
Filename Data Type | 185
Note that the expression (frame -1) is not necessarily integer in value. That
is, it could be 3.5 if rendering on fields. The extension will be converted to
an integer, however. Thus, the field where frame equals 4.0 and the field were
frame equals 4.5 will both generate “~/texture/hoops.4” in this example.
Light Data Type
Declaration:
light <name> (procedure=<procedure name>, <component list> ) ;
Reference:
<name> ( )
Literal:
light (<component list>)
Purpose:
This defines a source of illumination.
Comments:
A light is an object that may be instanced in the MODEL Section on page 37.
Light is used to illuminate a scene when the rendering mode is raytrace or
raycast. Lights are ignored when the rendering mode is wireframe. Only lights
of type spotlight can cast a shadow in the RayCaster, but any type of light
may cast a shadow in the RayTracer. A light may be specified as a literal or a
variable. If specified as a variable, it must have a name. Any of the following
components may be given between the parentheses. Please note that particle
system components are described following the light data type section.
■
active on page 192
■
ambient_shade on page 192
■
arc on page 193
■
bias on page 194
■
color on page 195
186 | Chapter 6 Data types
■
concentric on page 195
■
cone_end_radius on page 196
■
decay on page 197
■
decay_start on page 198
■
depth_input on page 199
■
depth_output on page 199
■
direction on page 200
■
directional on page 201
■
directionality on page 201
■
directional_turbulence on page 202
■
dropoff on page 203
■
dropoff_start on page 204
■
flare_color on page 204
■
flare_color_spread on page 205
■
flare_focus on page 205
■
flare_horizontal on page 206
■
flare_intensity on page 206
■
flare_length on page 207
■
flare_num_circles on page 207
■
flare_max_size on page 208
■
flare_min_size on page 209
■
flare_vertical on page 209
■
fog_intensity on page 210
■
fog_opacity on page 210
■
fog_radial_noise on page 211
■
fog_samples on page 212
■
fog_spread on page 212
Light Data Type | 187
■
fog_star_level on page 213
■
fog_type on page 214
■
fog_2D_noise on page 214
■
force_type on page 215
■
force_intensity on page 216
■
glow_intensity on page 216
■
glow_opacity on page 217
■
glow_radial_noise on page 218
■
glow_rotation on page 218
■
glow_spread on page 219
■
glow_star_level on page 220
■
glow_type on page 220
■
glow_2D_noise on page 222
■
halo_intensity on page 222
■
halo_spread on page 223
■
halo_type on page 224
■
hexagon_flare on page 225
■
intensity on page 226
■
LENS_FLARE on page 226
■
model on page 227
■
noise_threshold on page 229
■
noise_uoffset on page 229
■
noise_uscale on page 230
■
noise_voffset on page 231
■
noise_vscale on page 231
■
penumbra on page 232
■
psys_blob_lighting on page 258
188 | Chapter 6 Data types
■
psys_blob_map on page 259
■
psys_blob_noise on page 260
■
psys_blob_noise_frequency on page 260
■
psys_blob_threshold on page 261
■
psys_blur_quality on page 261
■
psys_branch_angle on page 262
■
psys_buoyancy on page 262
■
psys_collisions on page 263
■
psys_color on page 264
■
psys_curl on page 264
■
psys_density on page 265
■
psys_elasticity on page 266
■
psys_emission on page 266
■
psys_end_frame on page 267
■
psys_filename on page 267
■
psys_friction on page 268
■
psys_glow_intensity on page 268
■
psys_hair_length_max on page 269
■
psys_hair_length_min on page 269
■
psys_hair_stiffness on page 270
■
psys_hair_segments on page 271
■
psys_hit_method on page 271
■
psys_incandescence on page 272
■
psys_lifespan_min on page 273
■
psys_lifespan_max on page 273
■
psys_mass on page 274
■
psys_motion_type on page 275
Light Data Type | 189
■
psys_num_children on page 275
■
psys_parent_shading on page 276
■
psys_particles_per_sec on page 276
■
psys_randomization on page 277
■
psys_render_type on page 277
■
psys_size on page 278
■
psys_speed on page 279
■
psys_speed_decay on page 280
■
psys_speed_range on page 280
■
psys_split_time on page 281
■
psys_start_frame on page 281
■
psys_surface_shading on page 282
■
psys_time_random on page 283
■
psys_translucence on page 284
■
psys_transparency on page 284
■
psys_use_particle_file on page 285
■
radial on page 233
■
radial_noise_frequency on page 234
■
shadow on page 234
■
shadow_dither on page 235
■
shadowmult on page 236
■
shadowoffset on page 237
■
shadow_blend_offset on page 238
■
shadow_edge_quality on page 239
■
shadow_min_depth on page 239
■
shadow_output on page 240
■
shadow_resolution on page 241
190 | Chapter 6 Data types
■
shadow_samples on page 242
■
shape on page 243
■
shine_along on page 244
■
size on page 244
■
soft_shadows on page 245
■
specular on page 246
■
split_velocity_min on page 247
■
spread on page 247
■
star_points on page 248
■
torus_radius on page 248
■
turbulence_animated on page 249
■
turbulence_granularity on page 250
■
turbulence_intensity on page 250
■
turbulence_persistence on page 251
■
turbulence_roughness on page 252
■
turbulence_space_resolution on page 253
■
turbulence_spread on page 253
■
turbulence_time_resolution on page 254
■
turbulence_variability on page 254
■
up on page 255
■
use_old_shadow_map_algorithm on page 255
■
use_shadow_map on page 256
All components are specified using a keyword=value form. The components
may appear in any order. When more than one component is used, they must
be separated by commas. Not all components are optional. Components which
are not specified take on their default value. If any component is specified
more than once, the last such specification will be used, and all previous ones
will be ignored. Not all components are meaningful in all combinations. In
Light Data Type | 191
situations where a component is not meaningful, any specification of it will
be ignored with no ill effect.
Example:
light sun(model=directional, direction=(1,1,1));
active
Syntax:
active = <scalar>
Range:
0 (FALSE) or not 0 (TRUE).
Default:
TRUE
Purpose:
A switch which turns the light off if it is FALSE and on if it is TRUE.
Comments:
This component may be animated. active is appropriate for all lighting models.
Example:
active = fmod(frame,2)
ambient_shade
Syntax:
ambient_shade = <scalar>
Range:
0.0 to 1.0. Values outside this range are replaced by 0 or 1 as appropriate, and
a warning is issued.
192 | Chapter 6 Data types
Default:
0.5
Purpose:
Defines the omnidirectionality of an ambient light.
Comments:
This component may be animated. If ambient_shade is set to 0.0, the total
illumination will come from all directions and objects will show no edge
definition. Set to 1.0, the illumination will come solely from the light position
and objects will show definite edge contrast. ambient_shade is only appropriate
for the ambient lighting model.
Example:
ambient_shade = 1.0
arc
Syntax:
arc = <scalar>
Range:
0.0 to 360.0
Default:
360
Purpose:
This value defines the portion of the swept volume. A value of 360 degrees
represents the entire volume.
Comments:
This value is only applicable to the CONE, SPHERE, TORUS and CYLINDER
volume lights.
Light Data Type | 193
Example:
arc = 360.0
bias
Syntax:
bias = ( <scalar> , <scalar> )
Range:
Non-negative.
Default:
( 0.3, 0.4 )
Purpose:
This parameter is now obsolete
Used for RayCasting only. The two <scalar>s are interpreted as the minimum
and maximum values, respectively. Together they define the range for which
each surface point is randomly moved towards the eye before it is determined
whether or not it is in shadow. The minimum must be smaller than the
maximum. Either or both of the <scalar>s may be animated.
Comments:
The bias component is required to prevent incorrect self shadowing on an
object when a z value of a point on the surface is compared to the depth map
z from a nearby, but different point on the same surface. If the depth map z
is smaller, the point on the surface will appear to be in shadow when it isn’t.
The stochiastic bias allows the user to correct this while still allowing a surface
to curve over and legitimately shadow itself without aliasing. This,
unfortunately, has the effect of moving the shadow boundary away from its
true position. bias values must therefore be large enough to eliminate
self-shadowing artifacts, yet small enough to avoid any noticeable problems
from the offset boundary positions.
From a practical point of view, the minimum and maximum bias are measured
in world space and therefore depend on the size of the scene. For a 100 x 100
x 100 scene, a typical bias would be 0.3 to 0.4. If the shadow looks ragged in
places, increase the minimum and/or maximum. If the shadow boundary has
194 | Chapter 6 Data types
moved noticeably and looks incorrect, decrease the minimum and/or
maximum. For a 10 x 10 x 10 scene, a bias of 0.04 to 0.07 works well.
bias is appropriate for the spotlight lighting model. It is ignored for point,
infinite and ambient lights. It is ignored even for spotlights if shadow has not
been set to TRUE. Note that depth maps are only used for RayCasting.
Example:
bias = (0.4, 0.7)
color
Syntax:
color = <triple>
Range:
-infinity to infinity
Default:
( 255.0, 255.0, 255.0 )
Purpose:
This defines the color of the light.
Comments:
This component may be animated. A color component is appropriate for all
lighting models. Note that if you use a negative number, the light will suck
illumination away from the scene.
Example:
color = ( 0, 0, 255 )
concentric
Syntax:
concentric = <scalar>
Light Data Type | 195
Range:
-1.0 to 1.0
Default:
1.0
Purpose:
This value defines how much the in-out direction contributes to the light
direction.
This value defines the intensity of light radial to the light's central axis. For a
spherical volume light, a value of 1 imitates a point light with all illumination
moving out from the center. A value of -1 reverses that effect so that
illumination comes from the outside of the sphere towards the central axis.
With a value of 0, directional and radial values must be used to give
illumination direction along the major axis or radially around the major axis.
Example:
concentric = 0.25
cone_end_radius
Syntax:
cone_end_radius = <scalar>
Range:
-infinity to infinity
Default:
0.1
Purpose:
This value defines the radius of the end of the cone. A value of 0 makes the
volume light a true cone, whereas a value of 1 effectively reduces the shape
of the light to a cylinder. This value may be negative, which will have the
effect of reversing the direction of the cone.
196 | Chapter 6 Data types
Comments:
This value is only applicable to the CONE volume light.
Example:
cone_end_radius = 1.0
decay
Syntax:
decay = <scalar>
Range:
0, 1, 2, or 3. The value given is treated as an integer.
Default:
0
Purpose:
This is used to determine how intensity decreases with distance.
Comments:
This component may be animated. Set decay to 0 for constant intensity (the
light shines forever). Set decay to 1 for a decrease that is proportional to the
distance from the light. Set decay to 2 for a decrease that is proportional to
the square of the distance.Set decay to 3 for a decrease that is proportional to
the cube of the distance. decay is appropriate for point and spot lighting
models. It is ignored for directional and ambient lights.
For volume lights,
No decay
light reaches everything within the volume,
nothing outside.
>0
Light intensity decreases from the center
towards the edges of the volume.
Light Data Type | 197
0.5
linear dropoff from the middle to the
edges. With a value close to 1, intensity
drops off very fast from the middle With a
value close to 0, intensity drops off slowly
in the middle and fast near the edges.
<0
Light intensity decreases from the edges
towards the middle
Shape
Decay
BOX and SPHERE
all directions from the center
CYLINDER and CONE
in the direction of the principal axis
TORUS
perpendicular to the principal axis
Example:
decay = 2
decay_start
Syntax:
decay_start = <scalar>
Range:
0.0 to 1.0
Default:
0.0
Purpose:
This value defines how far out from the centre of the volume the decay starts.
198 | Chapter 6 Data types
Example:
decay_start = 0.0
depth_input
Syntax:
depth_input = <filename>
Range:
none
Default:
none
Purpose:
This is only relevant for a shadow-casting spot light. If there is a depth_input
file, then instead of generating the shadow map (expensive), it reads this file
instead to get the depth values. This is useful only for non-moving objects
and lights within the scene.
Example:
depth_input = “depth_input_file”
depth_output
Syntax:
depth_output = <filename>
Range:
none
Default:
none
Light Data Type | 199
Purpose:
This is only relevant for a shadow casting spot light. If there is a depth_output
file, then the shadow map generated is written to this file. This is useful if the
depth_input is also the same filename, which means the renderer will generate
the depth map just once, and write it to this file, then reuse it for subsequent
frames.
Example:
depth_output = “depth_output_file”
direction
Syntax:
direction = <triple>
Range:
unbounded, but cannot be (0,0,0).
Default:
( 0.0, 0.0, 1.0 )
Purpose:
This simulates placing the source of illumination at infinity.
Comments:
The triple provides a direction vector pointing towards the light. The
magnitude of the vector is immaterial. This component may be animated
using a motion path, or by otherwise varying the value of the triple. direction
is appropriate for the directional lighting model. It is ignored for point, spot,
ambient, area and linear lights
Example:
direction=(1,1,1)
200 | Chapter 6 Data types
directional
Syntax:
directional = <scalar>
Range:
-1.0 - 1.0
Default:
0.0
Purpose:
This value defines how much the primary axis direction contributes to the
light direction
Comments:
For volume lights only.
Example:
directional = 1.0
directionality
Syntax:
directionality = <scalar>
Range:
0.0 - 1.0
Default:
1.0
Light Data Type | 201
Purpose:
This value defines how much the direction of the light is taken into account
in the lighting calculation. A value of 0 acts like an ambient light; a value of
1 acts like a directional light.
Comments:
For volume lights only.
Example:
directionality = 1.0
directional_turbulence
Syntax:
directional_turbulence = <boolean>
Range:
ON/OFF
Default:
ON
Purpose:
Used to define a wind field.
Comments:
Turbulence is mostly used when the volume light is used to define a wind
field, but it also defines the light direction, and can be used to get flickering
sorts of light effects. The turbulence is defined as if it were inside a “box”, and
the box is placed appropriately when you need to evaluate the turbulence at
a point.
Example:
directional_turbulence = ON
202 | Chapter 6 Data types
dropoff
Syntax:
dropoff = <scalar>
Range:
If a negative number is provided, 0 is used; no error message is given. Although
any positive real number can be used, the dropoff will be severe beyond the
range of 5-7; numbers greater than 20 have little effect unless intensity is quite
high.
Default:
0
Purpose:
dropoff describes the rate at which illumination will fall off from the center
of a spot light to the edge of the cone of illumination (determined by the
angle set in spread). A value of 0 means there is no dropoff — the edge is as
bright as the center.
For volume lights, this value controls the rate at which light intensity decreases
from the center to the edge of the light. It only applies to CONE and CYLINDER
types of volume lights, and the dropoff is away from the principal axis of the
light. The range is from 0 to infinity. The range usually used is from 0 to 50.
Values of 1.0 and less give practically identical results, that is no discernible
intensity decrease along the radius of the beam. The default value is 0.0, which
means there is no dropoff. This is very similar to the way that spotlights work.
Comments:
This component may be animated. dropoff is appropriate for the spot lighting
model. It is ignored for point, directional and ambient lights.
Example:
dropoff = 0.5
Light Data Type | 203
dropoff_start
Syntax:
dropoff_start = <scalar>
Range:
0.0 to 1.0
Default:
0.5
Purpose:
This value defines how far out from the centre axis of the volume the drop-off
starts.
Example:
dropoff_start = 0.5
flare_color
Syntax:
flare_color = <triplet>
Range:
-infinity to infinity
Default:
(160, 160, 255)
Purpose:
If textured then each circle in the flare will contain the texture, scaled to
exactly fit inside the circle. Circular ramp textures can be used to create colorful
rainbow flare effects.
204 | Chapter 6 Data types
Example:
flare_color = (160, 160, 255),
flare_color_spread
Syntax:
flare_color_spread = <scalar>
Range:
0 to 1
Default:
0.5
Purpose:
This is the amount that the hue of individual circles is randomized about the
flare color. Note that the flare_color on page 204 must be at least partially
saturated (that is, not white or grey) to see this effect.
Example:
flare_color_spread = 0.5,
flare_focus
Syntax:
flare_focus = <scalar>
Range:
0 to 1
Default:
0.6
Light Data Type | 205
Purpose:
This controls the sharpness of circle edges. At a value of 1, the edges are totally
sharp, at zero the circles are very blurry.
Example:
flare_focus = 0.6,
flare_horizontal
Syntax:
flare_horizontal = <scalar>
Range:
-infinity to infinity
Default:
0
Purpose:
This parameter, with flare_vertical on page 209, controls the axis of the flare
effect relative to the center of the image. As the light source moves, the flare
will appear to rotate through this point.
Example:
flare_horizontal = 0,
flare_intensity
Syntax:
flare_intensity = <scalar>
Range:
0 to infinity
206 | Chapter 6 Data types
Default:
1
Purpose:
This is the scale for the brightness of the flare effect.
Example:
flare_intensity = 1,
flare_length
Syntax:
flare_length = <scalar>
Range:
0 to infinity
Default:
1
Purpose:
This controls how long the flare effect is relative to the light location. If the
value is small, then all the circles in the flare will bunch up on the light. If it
is large then the circles will get spread out off the edge of the image.
Example:
flare_length = 1,
flare_num_circles
Syntax:
flare_num_circles = <scalar>
Light Data Type | 207
Range:
0 to infinity
Default:
20
Purpose:
This is the number of spots created along the length of the flare effect.
Comment:
Very large numbers of spots can be expensive to render, especially if the size
is large and the flare color is textured.
Example:
flare_num_circles = 20,
flare_max_size
Syntax:
flare_max_size = <scalar>
Range:
-infinity to infinity
Default:
1
Purpose
The size of the circles is randomized between these two values.
Example:
flare_max_size = 1,
208 | Chapter 6 Data types
flare_min_size
Syntax:
flare_min_size = <scalar>
Range:
-infinity to infinity
Default:
0.1
Purpose:
The size of the circles is randomized between flare_min_size and flare_max_size
on page 208.
Example:
flare_min_size = 0.1,
flare_vertical
Syntax:
flare_vertical = <scalar>
Range:
-infinity to infinity
Default:
0
Purpose:
This parameter, with flare_horizontal on page 206, controls the axis of the flare
effect relative to the center of the image. As the light source moves, the flare
will appear to rotate through this point.
Light Data Type | 209
Example:
flare_vertical = 0,
fog_intensity
Syntax:
fog_intensity
Range:
-infinity to infinity
Default:
1.0
Purpose:
Set the brightness of the fog illumination.
Comments:
The fog illumination simulates a 3D volume of scattered light. Point lights
simulate a spherical volume of fog. If the fog_intensity is too high, then the
glow will look like a glowing orb. Use glow and/or halo effects in conjunction
with fog glow when a bright, focused center to the glow is desired.
Example:
fog_intensity = 0.5
fog_opacity
Syntax:
fog_opacity = <scalar>
Range:
-infinity to infinity
210 | Chapter 6 Data types
Default:
0.0
Purpose:
To allow an illuminated fog to obscure objects.
Comments:
Normally the fog glow is added on top of the light in the scene. If the opacity
is greater than zero, then the fog will be more opaque where it is brightest.
This is useful when simulating fire and smoke effects, which frequently do
not let all the light in a scene pass through. Black smoke can be created by
making the light color near black and the opacity high (around 10.0).
Example:
fog_opacity = 5.0
fog_radial_noise
Syntax:
fog_radial_noise = <scalar>
Range:
-infinity to infinity
Default:
0.0
Purpose:
To simulate explosion and starburst effects.
Comments:
Similar to glow_radial_noise on page 218.
NOTE This effect is currently two-dimensional.
Light Data Type | 211
Example:
fog_radial_noise = 0.5
fog_samples
Syntax:
fog_samples= <scalar>
Range:
Any value greater than 0 up to the resolution of the shadow depth map.
Default:
50
Purpose:
This parameter is only relevant when light fog shadows are to be computed.
The higher the value for this parameter, the better the fog shadow quality.
Usually, the default is good enough, but sometimes where there is little detail,
such a value can miss important fog shadow features, or produce noisy results.
By increasing this value (up to the depth map resolution), the quality will be
increased, but so will the performance.
Example:
fog_samples = 50;
fog_spread
Syntax:
fog_spread = <scalar>
Range:
-infinity to infinity
Default:
1.0
212 | Chapter 6 Data types
Purpose:
fog_spread has different effects on point lights and spot lights. On point lights,
it determines the size of the glowing spherical volume of fog. On spotlights,
it determines how concentrated or focused the beam is (higher fog_spread
creates more uniform spotlight beams, while at lower values, the center of the
beam will appear brighter).
Comments:
Use the decay on page 197 parameter on spot lights to modify the way the
beam falls off with distance from the lightsource.
Example:
fog_spread = .2
fog_star_level
Syntax:
fog_star_level = <scalar>
Range:
-infinity to infinity
Default:
0.0
Purpose:
To create radial explosion effects and control fog glow direction.
Comments:
See glow_star_level on page 220.
Example:
fog_star_level = 1.0
Light Data Type | 213
fog_type
Syntax:
fog_type = OFF | LINEAR_GLOW | EXPONENTIAL_GLOW | BALL_GLOW
Range:
0 (OFF) to 3 (BALL_GLOW)
Default:
OFF
Purpose:
The fog_type specifies the way that the intensity of fog illumination falls off
from the center of the light.
Comments:
All different types currently produce a LINEAR_GLOW; however, BALL_GLOW
will provide sharper thresholds at the edge when fog_opacity on page 210 is
not 0.0. In spot lights, the decay on page 197 will determine how fast the light
falls off from the center of the light.
Shadows can be cast into volumes of fog by using spot lights with shadow on
page 234 = ON and fog_type = LINEAR_GLOW (Raycaster Only).
Currently fog glow is only available for point lights and spot lights.
Example:
fog_type = LINEAR_GLOW
fog_2D_noise
Syntax:
fog_2D_noise = <scalar>
Range:
-infinity to infinity
214 | Chapter 6 Data types
Default:
0.0
Purpose:
Simulate smoke and fire effects using two-dimensional noise.
Comments:
The noise is generated on a plane that is centered at the location of the light
and always oriented towards the line of sight. To create the illusion of
illuminated smoke around a glowing light source, set fog_2D_noise to about
0.5 and animate slowly the noise_uoffset on page 229 and noise_voffset on
page 231 values. The smoke will appear to slowly drift by the light.
If a spotlight is rotated, the beam will appear to move through smoke in a
room. If you want the noise to remain locked on to the beam as it moves (for
example, for a rocket thruster), the glow_rotation on page 218 will need to be
animated to match the spotlight orientation.
Example:
fog_2D_noise = .5
force_type
Syntax:
force_type = OFF | GRAVITY | MAGNET | WIND | DRAG
Range:
As above
Default:
OFF
Purpose:
To define force emission from a light.
Light Data Type | 215
Example:
force_type = GRAVITY
force_intensity
Syntax:
force_intensity = <scalar>
Range:
-infinity to infinity
Default:
1.0
Purpose:
To set the intensity of the force.
Example:
force_intensity = 1.0
glow_intensity
Syntax:
glow_intensity = <scalar>
Range:
-infinity to infinity
Default:
1.0
Purpose:
Set the brightness of the light glow.
216 | Chapter 6 Data types
Comments:
If the light has a non-zero decay, then the brightness of the glow will vary
with the distance of the light. As the glow of the light becomes intense, the
size of the glow will appear to increase, especially when the center of the glow
washes out. This simulates what would naturally happen with a real light and
film. Negative glows will tend to subtract from other glows, thus a light with
a negative BALL_GLOW could be put along with a light with a standard glow,
resulting in a hole in the center of the glow.
Example:
glow_intensity = 3.0
glow_opacity
Syntax:
glow_opacity = <scalar>
Range:
-infinity to infinity
Default:
0.0
Purpose:
To allow a light glow to obscure objects.
Comments:
Normally the light glow is added on top of the light in the scene. If the opacity
is greater than zero, then the glow will be more opaque where it is brightest.
This is useful when simulating fire and smoke effects, which frequently do
not let all the light in a scene pass through. However, it is generally better to
use a fog glow for these effects. Also, if you want the glow to appear on the
background only, and not obscure any objects, then an opacity value of -1
will do this.
Light Data Type | 217
Example:
glow_opacity = 5.0
glow_radial_noise
Syntax:
glow_radial_noise = <scalar>
Range:
-infinity to infinity
Default:
0.0
Purpose:
To simulate starburst effects and eyelashes refracting light.
Comments:
Negative values will create a thicker noise. Use the radial_noise_frequency on
page 234 to adjust the smoothness of this effect.
Example:
glow_radial_noise = 0.5
glow_rotation
Syntax:
glow_rotation = <scalar> (in degrees)
Range:
-infinity to infinity
Default:
0.0
218 | Chapter 6 Data types
Purpose:
To rotate the various glow and fog noise and star effects about the location
of the light.
Comments:
Affects glow_2D_noise on page 222, fog_2D_noise on page 214, glow_star_level
on page 220, fog_star_level on page 213, glow_radial_noise on page 218 and
fog_radial_noise on page 211.
Example:
glow_rotation = 45.0
glow_spread
Syntax:
glow_spread = <scalar>
Range:
-infinity to infinity
Default:
1.0
Purpose:
glow_spread determines the general size of the glow effect.
Comments:
glow_spread also affects the size of the SPECTRAL and RAINBOW effects.
Negative values can have odd but useful effects. For example if the glow_spread
= -6.0 and the glow_2D_noise on page 222 = 1.0, an image of a fiery bubble is
created.
Example:
glow_spread = 0.1
Light Data Type | 219
glow_star_level
Syntax:
glow_star_level = <scalar>
Range:
-infinity to infinity
Default:
0.0
Purpose:
To simulate camera star filter effects.
Comments:
This is often effective when combined with a high frequency glow_radial_noise
on page 218. Use star_points on page 248 to set the number of points on the
star. If the star_points = 1.0, comet like effects are possible. The star can be
rotated by using glow_rotation on page 218.
Example:
glow_star_level = 4.0
glow_type
Syntax:
glow_type = OFF | LINEAR_GLOW | EXPONENTIAL_GLOW | BALL_GLOW |
SPECTRAL | RAINBOW | LENS_FLARE
Range:
0 (OFF) to 6 (LENS_FLARE)
Default:
OFF
220 | Chapter 6 Data types
Purpose:
The glow_type specifies the way that the intensity and color of a light glow
falls off from the center of the light.
Comments:
OFF
NO glow.
LINEAR_GLOW
glow slowly diminishes from center of light
EXPONENTIAL_GLOW
glow quickly diminishes from center of
light
BALL_GLOW
glow diminishes faster towards a distance
from glow center specified by the
glow_spread on page 219.
SPECTRAL
lower wavelengths (red) refract (or spread)
more than the higher frequencies (blue).
RAINBOW
simulates refraction due to water droplets
in air. The radius of the rainbow is determined by the glow_spread on page 219
parameter.
LENS_FLARE
concentric circles of color.
All the parameters associated with light glow work with all of the glow types.
For instance a RAINBOW glow may be combined with glow_star_level on page
220 of 1.0 and star_points on page 248 of 4 to create a colored refraction grating
effect.
Example:
glow_type = EXPONENTIAL
Light Data Type | 221
glow_2D_noise
Syntax:
glow_2D_noise = <scalar>
Range:
-infinity to infinity
Default:
0.0
Purpose:
Simulate smoke and fire effects using a two-dimensional noise.
Comments:
The noise is generated on a plane that is centered at the location of the light
and always oriented towards the line of sight. To create the illusion of
illuminated smoke around a glowing light source, set glow_2D_noise to about
0.5 and animate slowly the noise_uoffset on page 229 and noise_voffset on
page 231 values. The smoke will appear to slowly drift by the light.
Generally fog glow (fog_2D_noise on page 214) is better for creating smoke
and fire effects, because these are 3D effects. (glow_2D_noise on page 222
cannot be occluded by objects, for example.)
Example:
glow_2D_noise = .5
halo_intensity
Syntax:
halo_intensity
Range:
-infinity to infinity
222 | Chapter 6 Data types
Default:
1.0
Purpose:
Set the brightness of the light halo..
Comments:
If the light has a non-zero decay, the brightness of the halo will vary with the
distance of the light. As the halo of the light becomes intense, the size of the
halo will appear to increase, especially when the center of the halo washes
out.
Example:
halo_intensity = 3.0
halo_spread
Syntax:
halo_spread = <scalar>
Range:
-infinity to infinity
Default:
1.0
Purpose:
halo_spread determines the general size of the glow effect.
Comments:
halo_spread also affects the size of the RIM_HALO. Halo spread is generally
greater than the spread of the glow when the values are the same.
Light Data Type | 223
Example:
halo_spread = 0.1
halo_type
Syntax:
halo_type = OFF | LINEAR_GLOW | EXPONENTIAL_GLOW | BALL_GLOW |
LENS_FLARE | RIM_HALO
Range:
0 (OFF) to 5 (RIM_HALO)
Default:
OFF
Purpose:
The halo_type specifies the way that the intensity and color of a light halo
falls off from the center of the light.
Comments:
OFF
NO halo.
LINEAR_GLOW
halo slowly diminishes from center of light
EXPONENTIAL_GLOW
halo quickly diminishes from center of light
BALL_GLOW
halo diminishes faster towards a distance
from glow center specified by the
halo_spread on page 223.
LENS_FLARE
simulates a bright light source illuminating
the surfaces of several camera lenses. The
intensity of the flare is determined by the
halo_intensity on page 222. The size of the
224 | Chapter 6 Data types
circles created is relative to the field of view
of the camera.
RIM_HALO
This forms a circular ring with a soft central
glow. The size of the ring is determined by
the halo_spread on page 223. The halo of
a light is much the same as its glow, except
the falloff is generally more gradual, and
different falloff types are available.
Example:
halo_type = LENS_FLARE
hexagon_flare
Syntax:
hexagon_flare = <boolean>
Range:
Boolean(ON/OFF)
Default:
OFF
Purpose:
This turns on Hexagon shaped flare elements (instead of circles). Other shapes
are possible by texture mapping the flare color with an image of the desired
shape (white on black).
Example:
hexagon_flare = OFF,
Light Data Type | 225
intensity
Syntax:
intensity = <scalar>
Range:
-infinity to infinity
Default:
1.0
Purpose:
This sets the brightness of the light.
Comments:
This component may be animated. The value is checked at usage time, and if
negative, stops execution. Set intensity to 0.0 for no illumination, 1.0 for
normal illumination; 5.0 would be a very bright illumination. If you set
intensity to a negative number, it will suck light away from the scene.
Example:
intensity = 2
LENS_FLARE
Syntax:
LENS_FLARE = <boolean>
Range:
Boolean (OFF/ON)
Default:
OFF
226 | Chapter 6 Data types
Purpose:
To turn lens flare on or off.
Example:
LENS_FLARE = ON
model
Syntax:
model = ambient | area | directional | linear | point | spot | volume
Range:
As enumerated above.
Default:
None. Must be specified.
Purpose:
Specifies the lighting model used for this light. The possibilities are:
ambient
This is similar to a point light, except that
only a portion of the illumination emanates
from the point. The remainder of the illumination comes from all directions and
lights everything uniformly.
area
This is similar to a point light, except the
source of illumination is rectangular.
directional
In this case, the source of illumination is
infinitely far away from the scene. The actual position of the light data item in the
scene description is immaterial. Its orientation, however, is used. Rotations will affect
the direction of the light.
Light Data Type | 227
linear
This is similar to a point light, except the
source of illumination is a line of light
placed in the scene.
point
This is the case where light emanates from
a point somewhere in the scene. That point
is the same as the position of the light object in the scene description. (That is, the
origin of the light is (0,0,0) relative to the
light object, and is transformed using current_transformation.) Note that the light
emanates in all directions.
spot
This is similar to a point light in that it is a
point source, and it exists somewhere in
the scene. It is different, however, in that
it radiates illumination in a cone about a
specific direction. The position of the
source in the scene is the same as the position of the light object in the scene description. (That is, the origin of the light is
(0,0,0) relative to the light object, and is
transformed using current_transformation.)
volume
defines a closed volume in which objects
will be illuminated, and nothing outside
the volume is directly illuminated by the
light. Within the volume, the direction and
intensity can vary in many different parameters. A volume light is a convenient way
to “link” a light spatially, instead of by object. The main use of the volume light is
to be a force field generator and particle
emitter.
Comments:
The lighting model is not animatable. The value is checked to be one of the
above at definition time. Improper specification terminates execution with
an error message.
228 | Chapter 6 Data types
Example:
model = directional
noise_threshold
Syntax:
noise_threshold = <scalar>
Range:
0 to 1.0
Default:
1.0
Purpose:
This is a cutoff value for 2D noise. As the threshold is lowered to zero,
fog_2D_noise on page 214 and glow_2D_noise on page 222 break up into smaller
and smaller particles.
Comments:
This is useful for simulating globular clusters, ejecta from explosions, snow
and rain effects, especially when the noise u and v scale is high. It can also
help make flames and smoke more patchy.
Example:
noise_threshold = 0.8
noise_uoffset
Syntax:
noise_uoffset = <scalar>
Range:
-infinity to infinity
Light Data Type | 229
Default:
0.0
Purpose:
To offset the horizontal position of 2D noise.
Comments:
Can create the look of smoke moving past a light when animated. Rain and
snow effects are also possible.
NOTE The noise will wrap after an offset of 1.0, which is useful in creating animated
loops.
Example:
noise_uoffset = .5
noise_uscale
Syntax:
noise_uscale = <scalar>
Range:
0 to infinity
Default:
1.0
Purpose:
To change the scale of glow_2D_noise on page 222 and fog_2D_noise on page
214 in the horizontal.
Comments:
This is useful for creating effects like layered fog and tall flames. Also, if the
noise_uscale on page 230 and noise_vscale on page 231 are animated from high
to low values, the noise will appear to fly apart like an explosion.
230 | Chapter 6 Data types
Example:
noise_uscale = 3.0
noise_voffset
Syntax:
noise_voffset = <scalar>
Range:
-infinity to infinity
Default:
0.0
Purpose:
To offset the vertical position of the 2D noise.
Comments:
Can create the look of smoke moving past a light when animated. Rain and
snow effects are also possible.
NOTE the noise will wrap after an offset of 1.0, which is useful in creating animated
loops.
Example:
noise_voffset = .5
noise_vscale
Syntax:
noise_vscale = <scalar>
Range:
0 to infinity
Light Data Type | 231
Default:
1.0
Purpose:
To change the scale of the glow and fog 2D_noise in the vertical.
Comments:
This is useful for creating effects like layered fog and tall flames. Also, if the
noise_uscale on page 230 and noise_vscale on page 231 are animated from high
to low values, the noise will appear to fly apart like an explosion.
Example:
noise_vscale = 3.0
penumbra
Syntax:
penumbra = <scalar>
Range:
absolute: -90, 90 (degrees)
useful range: -20, 20
Purpose:
To determine the softness of the spot light’s edge. It is defined in degrees that
are relative to the edge of the spotlight’s spread.
The following illustrates the penumbra as the area where light falls when a
light bulb is partially eclipsed by a lamp shade. A penumbra displays the region
of partial shadowing of the dimension of the light source.
232 | Chapter 6 Data types
Comments:
This component may be animated.
Example:
penumbra = 20.0,
radial
Syntax:
radial = <scalar>
Range:
-1.0 - 1.0
Default:
0.0
Light Data Type | 233
Purpose:
This value defines how much the spin direction contributes to the field value.
Comments:
For volume lights only.
Example:
radial = 0.0
radial_noise_frequency
Syntax:
radial_noise_frequency = <scalar>
Range:
-infinity to infinity
Default:
0.5
Purpose:
To control the smoothness of the glow and fog radial noises.
Comments:
See glow_radial_noise on page 218.
Example:
radial_noise_frequency = 3.0
shadow
Syntax:
shadow = <scalar>
234 | Chapter 6 Data types
Range:
0 (FALSE) or not 0 (TRUE)
Default:
FALSE
Purpose:
A boolean indicating whether this light will cast shadows or not. If shadow
is TRUE, the light will cast shadows.
Comments:
This component may be animated. For RayCasting, shadow on page 234 is
appropriate for the spot lighting model and ignored for point, directional and
ambient lights. For RayTracing, shadow is appropriate for all lighting models.
Example:
shadow = TRUE
shadow_dither
Syntax:
shadow_dither = <scalar>
Range:
0.0 to 1.0
Default:
1.0
Purpose:
Values less than 1.0 allow a tradeoff between soft jittered shadow edges and
less noisy but more defined shadow edges.
Light Data Type | 235
Comments:
Used with soft shadowing in the raytracer. If this value is zero, then the soft
shadows will break apart into multiple shadows, determined by the
shadow_samples on page 242 parameter. If shadow_samples = 4, then the light
will appear to cast 4 separate shadows. The separation of the shadows is
determined by the light radius and the distance of the light away. As the
shadow_dither parameter is increased to 1.0, the four shadows would then
each spread until they merged into one soft shadow.
NOTE for animations it is best to leave this parameter at 1.0, because the shadows
may move a little as the view changes.
SEE soft_shadows on page 245.
Raytracer ONLY.
Example:
shadow_dither = 0.5
shadowmult
Syntax:
shadowmult = <scalar>
Range:
Not negative; effective range is 0.0 to 4.0
Default:
1
Purpose:
This parameter is obsolete effective this software release. Similar to blurmult
on page 368 for textures, shadowmult is a scaling factor for the size of the
sample region for the depth map. The default size of the sample region is 4 x
4 pixels in the depth map.
Values lower than 0.5 (without using shadowoffset) are prone to aliasing and
banding. The actual formula used to calculate the size of the sample area is:
236 | Chapter 6 Data types
numpixels = (4 * shadowmult) + shadowoffset
Care should be taken that numpixels does not become negative or 0.
shadowmult is appropriate for the spotlight lighting model. It is ignored for
point, infinite and ambient lights. It is ignored even for spotlights if shadow
has not been set to TRUE. Note that depth maps are only used for RayCasting.
shadowmult is meaningless and ignored when RayTracing.
Comments:
This component may be animated.
Example:
shadowmult = 3.0
shadowoffset
Syntax:
shadowoffset = <scalar>
Range:
unbounded; effective range is -2 to 8.
Default:
0
Purpose:
This parameter is obsolete effective this release. Similar to bluroffset on page
368 for textures, shadowoffset modifies the sampling region of the depth map.
shadowoffset adds a specified amount to the pixel area of the sampling region.
The default sampling region is 4 by 4 pixels in the depth map. The actual
formula used to calculate the sample region is:
numpixels = (4 * shadowmult) + shadowoffset
It is always square, numpixels to a side. Care should be taken that numpixels
does not become negative or 0. shadowoffset is appropriate for the spotlight
lighting model. It is ignored for point, infinite and ambient lights. It is ignored
even for spotlights if shadow has not been set to TRUE. Note that depth maps
Light Data Type | 237
are only used for RayCasting. shadowoffset is meaningless and ignored when
RayTracing.
Comments:
This component may be animated.
Example:
shadowoffset = 0.5
shadow_blend_offset
Syntax:
shadow_blend_offset = <scalar>
Range:
0 to infinity
Default:
1.0
Purpose:
This is useful for removal of self shadowing.
Comments:
shadow_blend_offset offsets the depth of the blended shadow samples, but
not the depth of the center sample. At zero, the sample region is a plane
tangent to the light direction vector. As the value increases, the sample region
becomes a cone with the outer edges towards the light. Its use is somewhat
similar to the old bias_max; however, it cleans up self-shadows without
sacrificing the tightness of a shadow relative to a very close object.
Raycast Shadows ONLY
Example:
shadow_blend_offset = .3
238 | Chapter 6 Data types
shadow_edge_quality
Syntax:
shadow_edge_quality = <scalar>
Range:
1 to infinity
Default:
2
Purpose:
Sets the blur filter size for shadow depth maps.
Comments:
At low values (1 or 2) slight staircasing can appear around shadow edges.
Increasing the shadow_edge_quality will correct this problem, but increase
rendering time a bit. Also the edge will become softer, requiring larger
shadow_resolution on page 241 values if hard edges are desired.
NOTE shadow_resolution should be used to control general level of blur, not
shadow_edge_quality.
NOTE Raycast Shadows ONLY
Example:
shadow_edge_quality = 3
shadow_min_depth
Syntax:
shadow_min_depth = <scalar>
Range:
0.0 to infinity
Light Data Type | 239
Default:
0.05
Purpose:
To correct self shadowing problems in raycast shadows. The shadow_min_depth
is the world space distance that a point is moved towards a spotlight before
shadowing is calculated.
Comments:
If this value is 0, than an object will shadow itself by 50% (if it casts shadows)
when the light is at an inclined angle to the surface. A relatively small
shadow_min_depth value can bring the surface out of its own shadow,
especially when combined with the shadow_blend_offset on page 238 parameter.
Also, if the surface does not need to cast shadows, only to receive them, turn
shadow casting off on the object (then a shadow_min_depth of 0 is fine). The
most typical example of this is a groundplane.
If shadow_min_depth is too high, shadows will not be cast from very close
objects.
This parameter is similar to the old bias_min parameter, but much smaller
correction values are now possible.
Raycast Shadows ONLY
Example:
shadow_min_depth = 0.03
shadow_output
Syntax:
shadow_output = <filename>
Range:
none
Default:
none
240 | Chapter 6 Data types
Purpose:
Specifies the file in which to store an 8-bit version of the depth map. This is
useful if you want to create a bump map from the geometry, but is not required
otherwise. shadow_output is appropriate for the spot lighting model. It is
ignored for point, infinite and ambient lights. It is ignored even for spotlights
if shadow on page 234 has not been set to TRUE. Note that depth maps are
only used for RayCasting. shadow_output is meaningless and ignored when
RayTracing. For details on the differences between RayCasting with shadows
and RayTracing, please refer to the User’s Guide.
Comments:
This component may be animated using the normal filename mechanisms.
Example:
shadow_output = “texture/new.bump” /* no frame extension */
or
shadow_output = (“texture/new.bump”frame) /* with frame extension
*/
shadow_resolution
Syntax:
shadow_resolution = <scalar>
Range:
any value between 8 and 8192
Default:
512
Purpose:
Defines the size of shadow depth maps used in raycasting. Large
shadow_resolution values provide sharper edged shadows but at a cost in
memory and rendering time.
Light Data Type | 241
Comments:
Very soft and smooth shadows are possible with a shadow_resolution setting
around 50. Low resolutions have the added advantage of being fast to render
and taking up little memory.
The shadow_resolution is the primary factor determining the softness of
shadows, but the spotlight spread on page 247 and shadow_edge_quality on
page 239 also affect the general level of blur. The shadow map is defined relative
to the cone of the spotlight; so a tightly focused spread will create sharper
shadows. A spread of 90 will require a shadow_resolution 2 times that of a
spread of 45 in order to match.
Raycast Shadows ONLY
Example:
shadow_resolution = 55
shadow_samples
Syntax:
shadow_samples = <scalar>
Range:
1 to infinity
Default:
2
Purpose:
Set the minimum number of shadow feeler rays per sample (used to create
raytracer soft shadows).
Comments:
A large value will result in slower rendering times, but smoother quality soft
shadows.
SEE soft_shadows on page 245
Raytracer ONLY.
242 | Chapter 6 Data types
Example:
shadow_samples = 8
shape
Syntax:
shape = BOX_VOLUME | SPHERE_VOLUME | CYLINDER_VOLUME |
CONE_VOLUME | TORUS_VOLUME
Range:
One of the above.
Default:
SPHERE_VOLUME
Purpose:
This defines the shape of the volume light in space. The choices are:
■
BOX
■
SPHERE
■
CYLINDER
■
CONE
■
TORUS
The shapes of the volume light can be further modified by applying
transformations to the dag node(s) above the volume light.
Comments:
Volume lights only.
Example:
shape = SPHERE_VOLUME
Light Data Type | 243
shine_along
Syntax:
shine_along = <triple>
Range:
Any set of coordinates in world space (but must be different than the light
itself).
Default:
( 0.0, 0.0, 0.0 )
Purpose:
The triple gives the x, y and z coordinates describing the location of the center
of illumination by the spotlight.
Comments:
This component may be animated using a motion path or by otherwise varying
the value of the triple. shine_along is appropriate for the spot lighting model.
It is ignored for point, directional and ambient lights.
Example:
shine_along = (20,5,-1)
size
Syntax:
size = <scalar>
Range:
Between 256 and 8192.
Default:
512
244 | Chapter 6 Data types
Purpose:
This parameter is obsolete effective this software release. size defines the
resolution of depth maps used to cast shadows when RayCasting. Increasing
the size will provide more detailed shadows, and will also increase the
rendering time and the amount of memory used. A size of 512 uses 1 Mbyte
of memory, a size of 1024 uses 4 Mbytes of memory.
Comments:
This component may be animated. size is appropriate for the spot lighting
model. It is ignored for point, directional and ambient lights. It is ignored
even for spotlights if shadow on page 234 has not been set to TRUE. Note that
depth maps are only used for RayCasting. The size component is meaningless
and ignored when RayTracing.
Example:
size = 256
soft_shadows
Syntax:
soft_shadows = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
FALSE
Purpose:
If TRUE, then soft shadowing is enabled in AliasStudio RayTracing.
Comments:
The nature of soft shadows created is determined by the distance of the light
from the object casting shadows, combined with the light_radius parameter.
Shadows are generated to match a globe-shaped light with the specified radius
(in world space units). If the light source is small and/or far away, then
Light Data Type | 245
hard-edged shadows will result. Shadows become softer-edged as the light’s
radius increases, as happens in the real world. However, because of
super-sampling, the region of partial shadow (penumbra on page 232) can
become noisy. To correct this, turn up the number of samples used, adjusting
either the shadow_samples on page 242 level (on the light) or the global
aalevelmin on page 54 and aalevelmax on page 53. Note that if fast_shading
on page 63 is turned on, the number of shadow samples per pixel will equal
the shadow_samples on page 242 level, and will not be affected by the aalevel.
Also, due to a blending function used, soft_shadows can be useful even when
the light_radius = 0 and the shadow_samples = 1. This method helps avoid
jaggies on shadow boundaries when fast_shading is used.
soft_shadows works for AliasStudio RayTracing only.
Example:
soft_shadows = TRUE
specular
Syntax:
specular = <boolean>
Range:
ON/OFF
Default:
ON
Purpose:
If set to ON, then the light will contribute to the specular component. It is
useful to turn this OFF when using a negative volume light to remove light.
Comments:
Volume lights only.
Example:
specular = ON
246 | Chapter 6 Data types
split_velocity_min
Syntax:
split_velocity_min = <scalar>
Range:
0 to infinity
Default:
5
Purpose:
Appears only if psys_collisions on page 263 are set to ON. This provides a limit
on the speed a particle must be moving when it collides with an object to
determine if the particle splits.
Example:
split_velocity_min = 5
spread
Syntax:
spread = <scalar>
Range:
2 to 179. The absolute value is used. This value is clipped to 179 if the
magnitude is too large. Similarly, if the magnitude is less than 0.2, it is set to
0.2 to avoid numeric instabilities.
Default:
40.0 (degrees)
Purpose:
spread provides the angle of illumination from a spotlight in degrees.
Light Data Type | 247
Comments:
This component may be animated. The smaller the value, the tighter the
spotlight will appear to be. If a negative value is specified, the sign is ignored.
spread is appropriate for the spot lighting model. It is ignored for point,
directional and ambient lights.
Example:
spread = 15
star_points
Syntax:
star_points = <scalar>
Range:
0 to infinity
Default:
4.0
Purpose:
To set the number of points on star filters. (see glow_star_level on page 220.)
Comments:
Values of 1 and 2 are frequency useful. For example if star_points = 1.0 and
glow_star_level = 1.0 and the glow_type on page 220 = RAINBOW, then a
familiar rainbow arch will be generated.
Example:
star_points = 5.0
torus_radius
Syntax:
torus_radius = <scalar>
248 | Chapter 6 Data types
Range:
-infinity to infinity
Default:
0.0
Purpose:
This is the ratio of the minor radius to the major radius. The default value of
0.5 gives a typical bagel, where the “hole” has been squashed down to a single
point.
Comments:
This value is only applicable to a TORUS volume light.
Example:
torus_radius = 0.5
turbulence_animated
Syntax:
turbulence_animated = <boolean>
Range:
ON/OFF
Default:
ON
Purpose:
The turbulence may be static, or it may vary over time. With static turbulence,
you get dappled lighting but it doesn’t change. With animated turbulence,
you get flickering light. In a static turbulent wind field, the eddies are always
in the same place: a stream of particles blowing through a static field would
always follow the same path. In an animated field, the path itself would swirl
and change.
Light Data Type | 249
Comments:
Volume lights only.
Example:
turbulence_animated = ON
turbulence_granularity
Syntax:
turbulence_granularity = <scalar>
Range:
0 to 1.0
Default:
0.0
Purpose:
This value defines the Low frequency cutoff. It is like a high pass filter. It
allows for grainy patterns of turbulence.
Comments:
Volume lights only.
Example:
turbulence_granularity = 0.0
turbulence_intensity
Syntax:
turbulence_intensity = <scalar>
Range:
0.0 to 1.0
250 | Chapter 6 Data types
Default:
0.0
Purpose:
This defines the degree to which a volume light is turbulent.
Comments:
The light or force direction is modified by the turbulence, such that when the
turbulence_intensity = 1.0 then the direction is totally the direction calculated
by the turbulence. When the turbulence_intensity = 0.5, then the direction
will be a 50/50 blend of turbulence and light. In the case of the default SPHERE
volume shape, a value of 0.5 would cause objects to move generally away from
the light, but in a turbulent fashion. If the turbulence_intensity = 1, then
objects would just swirl around in no particular direction. The decay of the
light is respected, however, so the objects would swirl more vigorously near
the light source. If you wish to increase the general level of force you must
use the light intensity on page 226 or force_intensity on page 216 parameter.
Note that this differs from the turbulence_intensity on page 112 in the
Environment dynamics section, as that value controls the overall intensity of
force.
For volume lights only.
Example:
turbulence_intensity = 0.0
turbulence_persistence
Syntax:
turbulence_persistence = <scalar>
Range:
0 to infinity
Default:
5.0
Light Data Type | 251
Purpose:
This value represents the time scale.
Comments:
Stretch out the turbulence so that it changes more slowly. For volume lights
only.
Example:
turbulence_persistence = 5.0
turbulence_roughness
Syntax:
turbulence_roughness = <scalar>
Range:
0 to 1.0
Default:
0.5
Purpose:
This value defines the High Frequency cutoff for the spatial portion of the
Fourier spectrum. It is like a low-pass filter.
Comments:
For volume lights only.
Example:
turbulence_roughness = 0.5
252 | Chapter 6 Data types
turbulence_space_resolution
Syntax:
turbulence_space_resolution = <scalar>
Range:
1 to 16
Default:
16
Purpose:
This defines how large the turbulence table is in X, Y, Z.
Comments:
Turbulence patterns match at the edges of the turbulence box, so that this
pattern is repeated seamlessly throughout the range of the volume light.
Example:
turbulence_space_resolution = 16
turbulence_spread
Syntax:
turbulence_spread = <scalar>
Range:
-infinity to infinity
Default:
0.5
Purpose:
This value represents the space scale.
Light Data Type | 253
Comments:
Scale the turbulence box so that the same amount of turbulence covers a larger
volume. Volume lights only.
Example:
turbulence_spread = 0.5
turbulence_time_resolution
Syntax:
turbulence_time_resolution
Range:
2 to 32
Default:
16
Purpose:
For animated turbulence, this defines the resolution in time. (i.e. this many
3-D tables are created).
Comments:
Volume lights only.
Example:
turbulence_time_resolution = 16
turbulence_variability
Syntax:
turbulence_variability
254 | Chapter 6 Data types
Range:
0 to 1.0
Default:
0.5
Purpose:
This value defines the High Frequency cutoff for the time portion of the Fourier
spectrum.
Comments:
Volume lights only.
Example:
turbulence_variability
up
NOTE up is reserved for future use. In this software release, it is commented out
when the SDL file is written from the AliasStudio package.
use_old_shadow_map_algorithm
Syntax:
use_old_shadow_map_algorithm = <scalar>
Range:
0 (FALSE) or non-0(TRUE)
Default:
FALSE
Light Data Type | 255
Purpose:
An improved shadow map algorithm was introduced in version 7 to improve
the resulting image quality. This should be able to replace the old technique.
However, there can be very isolated situations where the old technique is
desirable - in this case, turn this option ON
Example:
use_old_shadow_map_algorithm = FALSE;
use_shadow_map
Syntax:
use_shadow_map = <scalar>
Range:
0 (FALSE) or non-0(TRUE)
Default:
FALSE
Purpose:
This is relevant to the raytracer/powertracer only. It is now possible to do
shadow casting while in the raytracer (if this option is turned ON). This has
several advantages:
■
soft shadows in raytracing without much expense
■
can do light fog shadows with this option turned on.
Comments:
For raytracer/powertracer only.
Example:
use_shadow_map = FALSE;
256 | Chapter 6 Data types
Particle system keywords
The following components are shared by both Light and Shader data types,
with the exception of psys_bend_u and psys_bend_v, which are used only in
Shaders.
psys_bend_u
Syntax:
psys_bend_u = <scalar>
Range:
-infinity to infinity
Default:
0.0
Purpose:
To bend the emission of particles along the U direction.
Comment:
Particles are usually emitted along the normal to the surface. U bend specifies
how much the emission can bend in the U direction. A value of -1 means no
bend, a value of 1 means the particles are emitted tangent to the surface in
the U direction.
Example:
psys_bend_u = 0.0
psys_bend_v
Syntax:
psys_bend_v = <scalar>
Range:
-infinity to infinity
Light Data Type | 257
Default:
0.0
Purpose:
To bend the emission of particles along the V direction.
Comment:
Particles are usually emitted along the normal to the surface. V bend specifies
how much the emission can bend in the V direction. A value of -1 means no
bend, a value of 1 means the particles are emitted tangent to the surface in
the V direction.
Example:
psys_bend_v = 0.0
psys_blob_lighting
Syntax:
psys_blob_lighting = CONSTANT_LIGHTING | ILLUMINATED |
SELF_SHADOWING
Range:
■
CONSTANT_LIGHTING
■
ILLUMINATED
■
SELF_SHADOWING
Default:
CONSTANT_LIGHTING
258 | Chapter 6 Data types
Purpose:
A blob can have 3 kinds of lighting: CONSTANT, ILLUMINATED, or SELF
SHADOWING.
CONSTANT
that there is no contribution from any
lights; only the blob color is used.
ILLUMINATED
the lighting is calculated once per blob,
and the entire blob is illuminated to that
extent. If the blobs are discrete, sudden
changes in illumination may be noticeable.
SELF SHADOWING
the lighting ends up being on a per-pixel
basis, and is correspondingly slower than
the other methods.
Example:
psys_blob_lighting = CONSTANT_LIGHTING
psys_blob_map
Syntax:
psys_blob_map = Texture(rgb)
Range:
Texture(color)
Default:
(0,0,0)
Purpose:
If the Render Type is BLOBBY_SURFACE, the color can be texture mapped. A
surface texture will be mapped projecting from the eye point, so that it will
appear to follow the blob. A solid texture will be applied according to the solid
texture placement, so that the blobs will appear to move through the texture.
Light Data Type | 259
Example:
psys_blob_map = (0,0,0)
psys_blob_noise
Syntax:
psys_blob_noise = <scalar>
Range:
0 to infinity
Default:
0.0
Purpose:
A value greater than 0 makes the blobs look less regular. This helps hide the
fact that the underlying system may have a small number of large blobs.
Example:
psys_blob_noise = 0.0
psys_blob_noise_frequency
Syntax:
psys_blob_noise_frequency = <scalar>
Range:
-infinity to infinity
Default:
0.1
Purpose:
The noise frequency should be chosen according to the size of the particles.
260 | Chapter 6 Data types
Example:
psys_blob_noise_frequency = 0.1
psys_blob_threshold
Syntax:
psys_blob_threshold = <scalar>
Range:
0 to infinity
Default:
0.2
Purpose:
This value is the density at which we threshold the surface for Surf Shading
or BLOBBY_SURFACE rendering.
Example:
psys_blob_threshold = 0.2
psys_blur_quality
Syntax:
psys_blur_quality = <scalar>
Range:
0 to infinity
Default:
0.5
Light Data Type | 261
Purpose:
Blobs are generated along the path of the particle to get motion blur. If the
blur quality is high, the particles are small, and they travel a long way in one
frame, then a lot of blobs will be created for each frame. In which case,
rendering will be slow and a lot of memory will be used up.
Example:
psys_blur_quality = 0.5
psys_branch_angle
Syntax:
psys_branch_angle = <scalar>
Range:
-infinity to infinity
Default:
45
Purpose:
After splitting, child particles will move at this angle from the particles original
path (for collisions, this is the path AFTER the collision).
Comments:
Caution: large branch angles may result in the particles penetrating the object
that they were supposed to be colliding with.
Example:
psys_branch_angle = 45
psys_buoyancy
Syntax:
psys_buoyancy = <scalar>
262 | Chapter 6 Data types
Range:
-infinity to infinity
Default:
0.0
Purpose:
This value gives the particle additional velocity in the direction of gravity (a
positive is high, and a negative value is low).
Comment:
This parameter is only applicable to GAS particles.
Example:
psys_buoyancy = 0.0
psys_collisions
Syntax:
psys_collisions = <boolean>
Range:
Boolean (ON/OFF)
Default:
OFF
Purpose:
If this value is OFF, particles will not collide with any objects. If set to ON,
particles will collide with any collision walls that have been turned ON (see
Floor, ceiling, left, right, front, back, in the ENVIRONMENT Section on page
99 for more information), and any simulation objects that have particle
collisions set to ON.
Light Data Type | 263
Example:
psys_collisions = OFF
psys_color
Syntax:
psys_color = <triple>
Range:
Texturable rgb
Default:
(255,255,255)
Purpose:
The color of a particle can be set to a fixed value, or texture mapped over its
lifetime. If it is mapped, then the V values of the map are mapped onto the
particles' lifetime (a V-ramp is a good choice for a texture here).
Example:
psys_color = (255,255,255)
psys_curl
Syntax:
psys_curl = <scalar>
Range:
0 to infinity
Default:
0.0
264 | Chapter 6 Data types
Purpose:
This is the amount particles twist about their direction of motion. This is
especially useful with hair.
Comments:
As the twist approaches 1, the hair or trajectory will become more tightly
coiled, until at a value of 1 it will go around in a loop. To create more curls
in hair, the psys_hair_segments on page 271 value must be increased.
Example:
psys_curl = 0.0
psys_density
Syntax:
psys_density = <scalar>
Range:
-infinity to infinity
Default:
1.0
Purpose:
This is the visual density of the particles. Less dense particles will appear more
transparent, more dense ones will be more opaque. If density is 1, the
transparency of the object is used, if density is 0, the particles are completely
transparent). Self shadowing will be more visible in denser particles.
Example:
psys_density = 1.0
Light Data Type | 265
psys_elasticity
Syntax:
psys_elasticity = <scalar>
Range:
-infinity to infinity
Default:
0.5
Purpose:
The elasticity of an object determines the amount of damping of speed on
collision with another object. A value of 0 means all speed is lost, a value of
1 means the object bounces back with the same speed.
Example:
psys_elasticity = 0.5
psys_emission
Syntax:
psys_emission = <boolean>
Range:
Boolean (ON/OFF)
Default:
OFF
Purpose:
If Emit Particles is set to ON, particle parameters will be used.
266 | Chapter 6 Data types
Example:
psys_emission = OFF
psys_end_frame
Syntax:
psys_end_frame = <scalar>
Range
-infinity to infinity
Default:
10000
Purpose:
To indicate the last frame of animation for particle emission.
Example:
psys_end_frame = 10000
psys_filename
Syntax:
psys_filename = <filename>
Purpose:
This is the full path prefix for the particle file name. This field is set on the
shader when a simulation is run with Save Particles ON (see Anim Tools >
Run dynamics). The particles are saved in particle description files, one per
shader or light particle emitter, per frame.
Comments:
For example, if the particle emitting shader is called Shader#1, and you type
"test" when prompted for a Save Particles file location, then the particle files
will be stored in./user_data/<project>/sdl/test.psys/Shader#1.n, where n is the
Light Data Type | 267
frame number for that particle file. Alternately, you can type your own path
names for the directory where particle files are stored.
Example:
psys_filename = Shader#1
psys_friction
Syntax:
psys_friction = <scalar>
Range
0 to infinity
Default:
0.5
Purpose:
The coefficient of friction defines how much an object gets slowed down when
in contact with another object.
Example:
psys_friction = 0.5
psys_glow_intensity
Syntax:
psys_glow_intensity = <scalar>
Range:
0 to infinity
Default:
0
268 | Chapter 6 Data types
Purpose:
Particles can emit glow. See the section glow_intensity on page 216 and
following for information on glow parameters.
Example:
psys_glow_intensity = 0
psys_hair_length_max
Syntax:
psys_hair_length_max = <scalar>
Range:
0 to infinity
Default:
2.0
Purpose:
Used to determine the distance a particle can travel in a frame. Hair length is
randomized between the psys_hair_length_max and psys_hair_length_min
on page 269 values. These values, combined with the psys_hair_segments on
page 271 value, determine the psys_lifespan_min on page 273 and
psys_lifespan_max on page 273 for the particles generated in the Generation
window.
Example:
psys_hair_length_max = 2.0
psys_hair_length_min
Syntax:
psys_hair_length_min = <scalar>
Light Data Type | 269
Range:
0 to infinity
Default:
1.0
Purpose:
Used to determine the distance a particle can travel in a frame. Hair length is
randomized between the psys_hair_length_max on page 269 and
psys_hair_length_min on page 269 values. These values, combined with the
psys_hair_segments on page 271 value, determine the psys_lifespan_min on
page 273 and psys_lifespan_max on page 273 for the particles generated in the
Generation window.
Example:
psys_hair_length_min = 1.0
psys_hair_stiffness
Syntax:
psys_hair_stiffness = <scalar>
Range:
0 to infinity
Default:
0.1
Purpose:
As the stiffness of a hair approaches 1 it responds less and less to forces. Note,
however, that time lag effects are not affected by this parameter. To totally
remove the time lag effect, make the steps/frame for the simulation greater
than the value for psys_hair_stiffness on page 270 (and increase the
psys_particles_per_sec on page 276).
270 | Chapter 6 Data types
Example:
psys_hair_stiffness = 0.1
psys_hair_segments
Syntax:
psys_hair_segments = <scalar>
Range:
1 to infinity
Default:
10.0
Purpose:
This value is used to determine the number of line segments along the longest
strands of hair. If the emitter is in motion, the oldest particles will lag behind
where the lag time (in frames) equals the value set in Hair Segments and the
Start and End Frame values set in the Particle Emission window. This lag can
create a nice effect (like hair in water), but if it is too large, either reduce the
Hair Segments value, or increase the simulation's Start and End Frame values.
Comments:
Increasing the Start and End Frame values will require that you increase the
number of Particles/Second in the Generation window in order to generate
the same number of hairs.
Example:
psys_hair_segments = 10.0
psys_hit_method
Syntax:
psys_hit_method = BOUNCE | DIE | SPLIT
Light Data Type | 271
Range:
As above
Default:
BOUNCE
Purpose:
If particles have collision turned on, they can do one of three things when
they collide with an object.
BOUNCE
means the particles will bounce off the
surface of the object, subject to the elasticity of the particles and the surface.
DIE
means the particles will disappear the
frame after they collide.
SPLIT
means the particles will split into several
new particles, each of which inherit the
parent's age and lifetime. Particles must be
moving fast enough (> Split Vel. Min) in
order to split, otherwise they will just
bounce.
Example:
psys_hit_method = BOUNCE
psys_incandescence
Syntax:
psys_incandescence = texture(triple)
Range:
Texturable rgb
272 | Chapter 6 Data types
Default:
(0,0,0)
Purpose:
The Incandescence of a particle can be set to a fixed value, or texture mapped
over its lifetime. If it is mapped, then the V values of the map are mapped
onto the particles' lifetime (a V-ramp is a good choice for a texture here).
Example:
psys_incandescence = (0,0,0)
psys_lifespan_min
Syntax:
psys_lifespan_min = <scalar>
Range:
0 to infinity
Default:
10
Purpose:
This value defines the minimum lifespan of a particle in frames.
Example:
psys_lifespan_min = 10
psys_lifespan_max
Syntax:
psys_lifespan_max = <scalar>
Light Data Type | 273
Range:
0 to infinity
Default:
50
Purpose:
This value defines the maximum lifespan of a particle in frames. If min and
max are different, then particle lifetimes are uniformly distributed in the range
between them.
Example:
psys_lifespan_max = 50
psys_mass
Syntax:
psys_mass = <scalar>
Range:
0 to infinity
Default:
0.1
Purpose:
This value is the mass of an individual particle (in kilograms). It determines
how forces affect the particles. The lighter the particle, the more a force will
accelerate it.
Example:
psys_mass = 0.1
274 | Chapter 6 Data types
psys_motion_type
Syntax:
psys_motion_type = GAS | SOLID | HAIR
Range:
GAS
SOLID
HAIR
Default:
GAS
Purpose:
Select HAIR, SOLID or GAS particles. Gaseous particles follow the motion of
the air; they are only affected by Turbulence and Wind fields. Solid particles
have mass, and are affected by regular forces.
Example:
psys_motion_type = GAS
psys_num_children
Syntax:
psys_num_children = <scalar>
Range:
0 to infinity
Default:
2
Purpose:
This is the number of children that a splitting particle will generate.
Light Data Type | 275
Example:
psys_num_children = 2
psys_parent_shading
Syntax:
psys_parent_shading = <boolean>
Range:
Boolean (ON/OFF)
Default:
OFF
Purpose:
If this is ON, the particle gets the color of the point on the surface that it
emanated from. For a blob surface, the blobs inherit the parent's color texture
map.
Example:
psys_parent_shading = ON
psys_particles_per_sec
Syntax:
psys_particles_per_sec = <scalar>
Range:
0 to infinity, Texturable
Default:
300
276 | Chapter 6 Data types
Purpose:
This value defines how many particles are emitted from the object per second.
This is done in seconds so that the net effect is independent of frame rate.
Comments:
If particle emission is texture mapped, then the actual rate may be lower.
Example:
psys_particles_per_sec = 300
psys_randomization
Syntax:
psys_randomization = <scalar>
Range:
0 to infinity
Default:
0
Purpose:
Randomizes the branch angle by rotating it around the direction of particle
travel.
Example:
psys_randomization = 0
psys_render_type
Syntax:
psys_render_type = THIN_GAS | CLOUD | BLOBBY_SURFACE
Light Data Type | 277
Range:
THIN_GAS
CLOUD
BLOBBY_SURFACE
Default:
THIN_GAS
Purpose:
A particle can be rendered as THIN GAS, CLOUD or BLOBBY SURFACE.
THIN_GAS
best suited for fairly transparent particle
systems. This method is fast, as it uses the
average density of the particles along a ray
to calculate the particle systems contribution to a pixel.
CLOUD
for denser particle systems, is more accurate (but slower), and in fact must be used
if psys_blob_lighting on page 258 is set to
SELF_SHADOWING. This method calculates
the contribution of the blobs in sorted order front to back, so that the structure of
the individual blobs is more visible.
BLOBBY_SURFACE
renders the implicit surface created by the
blobs.
Example:
psys_render_type = THIN_GAS
psys_size
Syntax:
psys_size = <scalar>
278 | Chapter 6 Data types
Range:
0 to infinity, Texturable
Default:
0.5
Purpose:
The (world space) size of a particle may be set to a fixed value, or texture
mapped over its lifetime. If it is mapped, then the V values of the map are
mapped onto the particles' lifetime (a V-ramp is a good choice for a texture
here). As the size of individual blobs gets larger and overlap increases, rendering
time will increase.
Comments:
This size is also used for buoyancy calculations for solid particles, so that a
particle that ends up much less dense than the medium may end up rising
very rapidly.
Example:
psys_size = 0.5
psys_speed
Syntax:
psys_speed = <scalar>
Range:
-infinity to infinity, Texturable
Default:
5.0
Purpose:
This value defines the average speed of particles being emitted.
Light Data Type | 279
Example:
psys_speed = 5.0
psys_speed_decay
Syntax:
psys_speed_decay = <scalar>
Range:
-infinity to infinity
Default:
0.8
Purpose:
This value is a multiplier which determines how fast a particle loses its initial
velocity. A value of 0 means the initial velocity is lost immediately, a value
of 1 means its initial velocity is retained indefinitely. This value is only
applicable to GAS particles.
Example:
psys_speed_decay = 0.8
psys_speed_range
Syntax:
psys_speed_range = <scalar>
Range:
-infinity to infinity
Default:
0.1
280 | Chapter 6 Data types
Purpose:
This value defines how much the emission speed of the particles can vary.
The speed at which a particle is emitted varies in the range (speed - speed
range, speed + speed range). If Speed Range is 0, all particles are emitted at
the average speed.
Example:
psys_speed_range = 0.1
psys_split_time
Syntax:
psys_split_time = <scalar>
Range:
0-1
Default:
0
Purpose:
Particles may split spontaneously (once per particle) as well as on collision.
The Split Time is the fraction of their lifetime at which they will split. A value
of 0 (particle birth) or 1 (particle death) will not cause any splitting.
Example:
psys_split_time = 0.01
psys_start_frame
Syntax:
psys_start_frame = <scalar>
Range:
-infinity to infinity
Light Data Type | 281
Default:
1
Purpose:
Particles are emitted starting at this frame. The start frame can be set earlier
than the animation start frame in order to "run up" the particle system.
Running up the particle system allows the first frame to show a particle effect
in mid motion rather than just starting.
Example:
psys_start_frame = 1
psys_surface_shading
Syntax:
psys_surface_shading = <scalar>
Range:
0 to 1.0
Default:
0.0
Purpose:
This parameter controls the level of shading on the surface of the particle
system. It behaves somewhat differently depending on the Motion Type and
Render Type selected. If the Render Type is BLOBBY_SURFACE or the Motion
Type is HAIR, it controls specular illumination. As the value approaches 1.0
the highlight becomes more intense and focused.
Comments:
For the best results when rendering hair, the Render Type should be CLOUD.
If the Render Type is THIN_GAS or CLOUD and the motion type is anything
but HAIR, the Surf Shading controls the amount of diffuse illumination at the
surface of the particle mass. The surface of the cloud for this shading is
282 | Chapter 6 Data types
controlled using the psys_blob_threshold on page 261 parameter. As the value
approaches 1.0, the shading of a cloud becomes completely surface shaded,
with no volume illumination of the particles.
If this is non-zero, it uses the psys_blob_threshold to create a "virtual surface"
which will provide normals to be used in the shading calculation. Increasing
the surface shading will give the blobs sharper edges, (for example, clouds
have a large surface shading component). A value of 1 means diffuse surface
illumination, a value of 0 means blob illumination.
NOTE Because normals are provided, the rendering is slower when the Surf
Shading value is non-zero.
Example:
psys_surface_shading = 0.5
psys_time_random
Syntax:
psys_time_random = <boolean>
Range:
Boolean (ON/OFF)
Default:
ON
Purpose:
If time random is OFF, particles will be emitted from the same spot on the
surface every frame. If set to ON, particles will be emitted from different spots
every frame.
Example:
psys_time_random = ON
Light Data Type | 283
psys_translucence
Syntax:
psys_translucence = <scalar>
Range:
0 to 1
Default:
0.6
Purpose:
Translucence is the extent to which diffuse light can penetrate the object. The
translucence of a particle can be set to a fixed value, or texture mapped over
its lifetime. If it is mapped, then the V values of the map are mapped onto
the particles' lifetime (a V-ramp is a good choice for a texture here).
Example:
psys_translucence = 0.6
psys_transparency
Syntax:
psys_transparency = <triple>
Range:
Texturable rgb
Default:
(0,0,0)
Purpose:
The transparency of a particle can be set to a fixed value, or texture mapped
over its lifetime. If it is mapped, then the V values of the map are mapped
onto the particles' lifetime (a V-ramp is a good choice for a texture here).
284 | Chapter 6 Data types
Comment:
Remember that the net transparency of the object will also depend on its size.
Smaller and/or less dense particles will appear more transparent anyway.
Example:
psys_transparency = (0,0,0)
psys_use_particle_file
Syntax:
psys_use_particle_file = <boolean>
Range:
Boolean (ON/OFF)
Default:
OFF
Purpose:
If set to ON, particles will not be generated during the simulation, but will be
read from files instead. These files would have been generated by previous
simulations or come from external sources.
Comments:
See the File Formats section of the Reference Guide for information on Particle
File Formats.
Example:
psys_use_particle_file = OFF
Light Data Type | 285
Motion_curve Data Type
Declaration:
motion_curve <name> ( <curve>, in = <pre extrapolation type>, out = <post
extrapolation type> )
Reference:
<name>
Literal:
motion_curve ( <curve>,
in = <pre extrapolation type>, out = <post extrapolation type> )
Purpose:
This allows you to specify a 3D spline curve to be used for animation. Usually
the spline curve is used as a motion path. The extrapolation type arguments
define how to evaluate the curve outside of its usual range. The motion_curve
data type is usually used in conjunction with the extract and animate
functions.
Example:
motion_curve motion_path ( curve#2,
in = PRE_CONSTANT, out = POST_CONSTANT );
Parameter_curve Data Type
Declaration:
parameter_curve <name> ( in = <pre extrapolation type>, out = <post
extrapolation type>, cvs = ( <parameter_vertex>, <parameter_vertex>, ... ))
In version 7, pc is a shorter keyword name for parameter_curve that can be
used interchangeably.
286 | Chapter 6 Data types
Reference:
<name>
Literal:
parameter_curve (
in = <pre extrapolation type>, out = <post extrapolation type>,
cvs = ( <parameter_vertex>, <parameter_vertex>, ... ) )
Purpose:
This allows you to define a two-dimensional parameter curve. A
parameter_curve may be specified as a literal or as a variable. If specified as a
variable, it must have a name. A parameter curve is usually used for the
animation of a scalar.
The shape of the parameter curve is defined by the list of <parameter_vertex>
arguments (See Parameter_vertex Data Type on page 288 for more information).
The extrapolation type arguments define how to evaluate the curve outside
of its usual range. The <pre extrapolation type> argument defines the shape
of the curve before the time value of the first <parameter_vertex> argument
defining the curve. The <post extrapolation type> defines the shape of the
curve after the time value of the last <parameter_vertex> argument defining
the curve.
NOTE For animation curves that contain just a constant value, it will be written
out as a scalar definition in version 7. This is for faster processing during rendering
as well as reduced SDL filesizes
Example:
parameter_curve plane.Z_Position (
in = PRE_CONSTANT, out = POST_CONSTANT,
cvs = (
parameter_vertex( 1.0, 0.0, TAN_SMOOTH, (-0.99676, 0.08042),
TAN_SMOOTH, (0.99676, -0.08042) ),
parameter_vertex( 10.0, -0.72613, TAN_SMOOTH, (-0.99676, 0.08042),
TAN_SMOOTH, (0.99676, -0.08042) )
)
);
Parameter_curve Data Type | 287
Parameter_vertex Data Type
Declaration:
parameter_vertex <name> ( <scalar>, <scalar>, <tangent type>, (<scalar>,
<scalar>), <tangent type>, (<scalar>, <scalar>) )
In version 7, pv is a shorter keyword name for parameter_vertex that can be
used interchangeably.
Reference:
<name>
Literal:
parameter_vertex ( <scalar>, <scalar>,
<tangent type>, ( <scalar>, <scalar> ),
<tangent type>, ( <scalar>, <scalar> ) )
Purpose:
This allows you to define in and out tangents at a keyframe point on a
two-dimensional parameter curve. A parameter_vertex may be specified as a
literal or as a variable. If specified as a variable, it must have a name. A
collection of these form a two-dimensional parameter curve which can be
used for animation of a scalar. All components of a parameter_vertex are given
by position, not by keyword. They are interpreted as:
keyframe time, keyframe value, in tangent type, (in tangent x,
y), out tangent type, (out tangent x, y)
The first and second parameters specify the value for the parameter curve at
a point in time. If the in/out tangent type is TAN_FIXED then the in/out
tangent x, y values specify the direction of a tangent vector which represents
the slope of the parameter curve as it enters/leaves the given keyframe. Varying
the direction of the tangent vector can be used to control the shape of the
curve before/after the keyframe.
In order to have a continuous animation, the tangent in vector and the tangent
out vector at a parameter_vertex should both point in a “forwards” direction.
Discontinuities can be introduced by making them point in different directions.
288 | Chapter 6 Data types
When in/out tangent types other than TAN_FIXED are chosen the tangent x,
y values are ignored and the specified tangent type is used to determine the
shape of the curve before/after the keyframe.
Example:
parameter_vertex ( 1, 0, TAN_FIXED, (-1,-1), TAN_LINEAR, (1,1) );
Patch Data Type
Declaration:
patch <name> ( <component list> );
Reference:
<name>
Literal:
patch ( <component list> )
Purpose:
A patch is a NURBS surface. It may be instanced as an object in the MODEL
Section on page 37. A curved or flat surface with smooth or hard edges can
be created with a NURBS. A patch may be specified as a literal or as a variable.
If specified as a variable, it must have a name. Any of the following
components may be specified between the parentheses:
■
active on page 291
■
casts_shadow on page 292
■
clusters on page 293
■
curvature on page 294
■
cvs on page 295
■
divisions on page 296
■
doublesided on page 297
■
end on page 298
Patch Data Type | 289
■
light_list on page 298
■
mate_curve on page 299
■
mate_patch on page 299
■
mate_type on page 300
■
motion_blur on page 300
■
motion_blur_shading_samples on page 301
■
motion_blur_texture_sample_level on page 301
■
name on page 302
■
particle_collisions on page 302
■
opposite on page 303
■
shader on page 304
■
shared_edge on page 304
■
start on page 306
■
subdivide on page 307
■
trim_region on page 307
■
trim_hole on page 309
■
type on page 310
■
uclosed on page 310
■
uknots on page 311
■
vclosed on page 311
■
vknots on page 312
■
udegree on page 313
■
vdegree on page 313
All components are specified using a keyword=value form. Components are
separated by commas. Of the above components, cvs on page 295, uknots on
page 311 and vknots on page 312 are required. Not all components are optional.
The components may be specified in any order. Components which are not
specified take on their default value. There may be any number of trim_region
290 | Chapter 6 Data types
on page 307s. If any component other than trim_region is specified more than
once, the last such specification will be used, and all previous ones ignored.
Example:
patch square_patch ( divisions = (8, 8),
shader = pink,
cvs = ( ( cv( ( 1.5, 0.0, -1.5 ), 1.0 ),
cv( ( 0.5, 0.0, -1.5 ), 1.0 ),
cv( ( -0.5, 0.0, -1.5 ), 1.0 ),
cv( ( -1.5, 0.0, -1.5 ), 1.0 ) ),
( cv( ( 1.5, 0.0, -0.5 ), 1.0 ),
cv( ( 0.5, 0.0, -0.5 ), 1.0 ),
cv( ( -0.5, 0.0, -0.5 ), 1.0 ),
cv( ( -1.5, 0.0, -0.5 ), 1.0 ) ),
( cv( ( 1.5, 0.0, 0.5 ), 1.0 ),
cv( ( 0.5, 0.0, 0.5 ), 1.0 ),
cv( ( -0.5, 0.0, 0.5 ), 1.0 ),
cv( ( -1.5, 0.0, 0.5 ), 1.0 ) ),
( cv( ( 1.5, 0.0, 1.5 ), 1.0 ),
cv( ( 0.5, 0.0, 1.5 ), 1.0 ),
cv( ( -0.5, 0.0, 1.5 ), 1.0 ),
cv( ( -1.5, 0.0, 1.5 ), 1.0 ) ) )
);
active
Syntax:
active = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Purpose:
A Boolean flag that controls whether the patch is visible or not.
Patch Data Type | 291
Comments:
This component may be animated. This is provided so you no longer have to
scale objects in an animation to 0 or translate them outside the scene for
frames in which they shouldn’t appear.
Example:
active = FALSE
casts_shadow
Syntax:
casts_shadow = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Purpose:
A Boolean that controls whether or not this patch will cast a shadow.
Comments:
This component may be animated.
NOTE A surface with transparent or semi-transparent shading will not cast a
shadow when RayCasting.
Example:
casts_shadow = FALSE
292 | Chapter 6 Data types
clusters
Syntax:
clusters = (<cluster matrix list>),
Range:
N/A
Default:
None.
Purpose:
A list of cluster matrices that affect the current surface.
Comments:
A cluster matrix describes the initial position of the matrix (4X4 scalars), the
type of cluster effect (JOINT or LEAF), JOINT level (or 0 if the type is LEAF),
and translate, rotate, scale as 3 scalar tuples.
Patch Data Type | 293
Example:
clusters = (
clm( CL_r_peak,
1.0
, 0.0
, 0.0
,
0.0
, 1.0
, 0.0
,
0.0
, 0.0
, 1.0
,
0.283681 , 0.0285822, -0.5841172,
LEAF, 0,
0.0
, 0.0
, 0.0
,
0.0
, 0.0
, 0.0
,
1.0
, 1.0
, 1.0
),
clm( CL_knot45_section0_Rwrist,
1.0
, 0.0
, 0.0
,
0.0
, 1.0
, 0.0
,
0.0
, 0.0
, 1.0
,
0.283681 , 0.0285822, -0.5841172,
LEAF, 0,
0.0
, 0.0
, 0.0
,
0.0
, 0.0
, 0.0
,
1.0
, 1.0
, 1.0
)
clm( CL_cluster#10,
1.0
, 0.0
, 0.0
,
0.0
, 1.0
, 0.0
,
0.0
, 0.0
, 1.0
,
0.283681 , 0.0285822, -0.5841172,
JOINT, 3,
-0.2398842, -0.0303474, 0.0
,
0.0
, 0.0
, 0.0
,
1.0
, 1.0
, 1.0
)
0.0
0.0
0.0
1.0
,
,
,
,
0.0
0.0
0.0
1.0
,
,
,
,
0.0
0.0
0.0
1.0
,
,
,
,
),
curvature
Syntax:
curvature = <scalar>
Range:
0 to 1. Values outside the range [0, 1] are clipped to 0 and 1 respectively.
294 | Chapter 6 Data types
Default:
0.96
Purpose:
This controls the threshold for adaptive subdivision.
Comments:
It may be animated. For good quality, use .90 and above. The larger the
curvature value, the more the curve will be subdivided. This is ignored if
uniform subdivision is being used.
Example:
curvature = 0.99
cvs
Syntax:
cvs = ( ( <cv>, <cv>, … <cv> ),
( <cv>, <cv>, … <cv> ),
.
.
.
( <cv>, <cv>, … <cv> ) )
Range:
Any collection of valid cvs (for more information about valid cvs, see the CV
Data Type).
Default:
None. Must be specified.
Purpose:
This defines the control vertices for the patch.
Patch Data Type | 295
Comments:
It may be animated. The CVs will be interpreted in the sequence
(( cv[u=0,v=0], cv[u=0,v=1], cv[u=0,v=2], cv[u=0,v=3] ),
( cv[u=1,v=0], cv[u=1,v=1], cv[u=1,v=2], cv[u=1,v=3] ),
( cv[u=2,v=0], cv[u=2,v=1], cv[u=2,v=2], cv[u=2,v=3] ),
( cv[u=3,v=0], cv[u=3,v=1], cv[u=3,v=2], cv[u=3,v=3] ))
Note that this is the same sequence as previous versions.
Example:
cvs = ( ( cv((3,0,-3),1), cv((1,0,-3),1), cv((-1,0,-3),1),
cv((3,0,-3),1)),
( cv((3,0,-1),1), cv((1,0,-1),1), cv((-1,0,-1),1), cv((-3,0,1),1)),
( cv((3,0, 1),1), cv((1,0,1),1), cv((-1,0, 1),1), cv((-3,0,
1),1)),
( cv((3,0, 3),1), cv((1,0,3),1), cv((-1,0, 3),1), cv((-3,0,
3),1)),)
divisions
Syntax:
divisions = ( <scalar>, <scalar> )
Range:
See subdivide on page 307. If adaptive, then divisions takes powers of 2 in the
range 1 to 128. If uniform, it uses integers greater than zero.
Default:
None. Must be specified.
Purpose:
This specifies the number of arc subdivisions.
296 | Chapter 6 Data types
Comments:
This component may be animated. If uniform subdivision is being used, then
the first scalar specifies the number of arc subdivisions in the u direction, and
the second scalar specifies the number in the v direction. If adaptive
subdivision is being used, then this component specifies the minimum and
maximum subdivision, respectively, to be used. Note that the minimum and
maximum actually used by adaptive subdivision will be the closest power of
2 greater than or equal to that given.
Example:
divisions = ( 2, 4 )
doublesided
Syntax:
doublesided = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE; that is, the patch will be doublesided.
Purpose:
The scalar will be interpreted as a Boolean, with 0 being FALSE and any other
value TRUE. If doublesided is FALSE, rendering proceeds more quickly, but
only one side of the surface is rendered. For most objects other than closed
surfaces, doublesided = TRUE is desirable. The reader is warned that with the
raytracer, rays may strike the object from any direction.
Comments:
This component may be animated.
Example:
doublesided = FALSE
Patch Data Type | 297
end
Syntax:
end = ( <scalar>, <scalar>),
Range:
Limited by surface’s parametric space
Default:
None. Must be specified.
Purpose:
This defines the end of a shared edge for a world-space texture.
Example:
end = (
1.5307337,
5.0
)
light_list
Syntax:
light_list = ( <light>, <light>, … <light> )
Range:
Each light given must have been defined; literals may not be used.
Default:
See below.
Purpose:
Each item referenced must be the name of a previously declared light data
item, or an array element of type light (See Light Data Type on page 186 for
more information). Literals may not be used. This lists the lights to be used
by this patch. If light_list is omitted or if it is specified and is empty, all
nonexclusive lights are used to illuminate the patch. If light_list is specified,
and the list contains defined lights, then all instances of those lights in the
298 | Chapter 6 Data types
scene, and only those, will be used for this patch. This enables situations where
the user may want 10 lights on a particular object, for example, but only two
lights on the rest of the scene.
Comments:
This component may not be animated.
Example:
light_list = ( spot01, spot02, flood, globallight )
mate_curve
Syntax:
mate_curve = ( <name of mate>)
Default:
None. Must be specified if shared_edge on page 304 is specified.
Purpose:
This specifies the mated curve that the current shared_edge is to be matched
up with for world-space texturing.
Example:
mate_curve = trim273932360
mate_patch
Syntax:
mate_patch = ( <name of joined patch>),
Default:
None. Must be specified if shared_edge on page 304 is specified.
Patch Data Type | 299
Purpose:
This specifies the mated patch that the current shared_edge is to be matched
up with for world-space texturing.
Example:
mate_patch = plane
mate_type
Syntax:
mate_type = <type of surface>,
Default:
None. Must be specified if shared_edge on page 304 is specified.
Purpose:
This specifies the type of surface that the current shared_edge is to be matched
up with for world-space texturing.
Example:
mate_type = TRIM
motion_blur
Syntax:
motion_blur = <scalar>
Default:
ON
Range:
0 (OFF) or non-zero (ON)
300 | Chapter 6 Data types
Purpose:
If motion_blur_on on page 74 is set for the file, this flag indicates that motion
blur should be calculated for this object.
Example:
motion_blur = ON
motion_blur_shading_samples
Syntax:
motion_blur_shading_samples = <scalar>
Default:
3 - for bump or displacement mapped objects
1 - for all other objects
Range:
>= 3 for bump or displacement mapped objects
> 0 for all other objects
Purpose:
If motion_blur_on on page 74 is set for the file, this flag indicates the number
of samples done for shading of motion-blurred objects.
Example:
motion_blur_shading_samples = 1
motion_blur_texture_sample_level
Syntax:
motion_blur_texture_smaple_level = <scalar>
Default:
3
Patch Data Type | 301
Range:
0-5
Purpose:
If motion_blur_on on page 74 is set for the file, this flag indicates the level of
sampling done for texturing of motion-blurred objects. A 0 indicates no extra
samples (lowest quality) and 5 means highest quality motion-blurred textures.
NOTE This flag does not apply to bump or displacement mapping.
Example:
motion_blur_texture_samples = 3
name
Syntax:
name = ( <name>)
Default:
None. If the mate_type on page 300 is parametric, a name is not required.
Names are required if the mate_type is a trim, due to ambiguities.
Purpose:
This gives a unique name to the shared_edge on page 304 being world-space
textured.
Example:
name = trim273932360
particle_collisions
Syntax:
particle_collisions = BOUNDING_BOX_COLLISIONS | OFF |
GEOMETRY_COLLISIONS
302 | Chapter 6 Data types
Range:
As above
Default:
OFF
Purpose:
To define which objects collide with particles.
Example:
particle_collisions = BOUNDING_BOX_COLLISIONS
opposite
Syntax:
opposite = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
FALSE
Purpose:
To reverse the sense of direction of the normal for the patch.
Comments:
This component may be animated. If doublesided on page 297 is FALSE (for
example, for faster execution), opposite can be used to reverse the orientation
of the backfacing and frontfacing parts of the patch. This may be done in
order to correct potential visibility problems.
Example:
opposite = TRUE
Patch Data Type | 303
shader
Syntax:
shader = (<shader>)
or
shader = ( <shader>, <shader>, … <shader> )
Range:
The shaders given may be variables or array elements of type shader (see Shader
Data Type on page 331 for more information). Note that there is no such thing
as a literal shader.
Default:
None. Must be specified.
Purpose:
This specifies which shading characteristics are assigned to the surface.
Comments:
This component may be animated. If a list of shaders is specified, they will
be visible in the order given.
Example:
shader = (pink)
shared_edge
Syntax:
shared_edge = (
(
type <name>,
start = ( <scalar>, <scalar>),
end = ( <scalar>, <scalar>),
304 | Chapter 6 Data types
name = <name>,
mate_patch = <name>,
mate_type = <curve type>
),
(
type <name>,
start = ( <scalar>, <scalar>),
end = ( <scalar>, <scalar>),
name = <name>,
mate_patch = <name>,
mate_type = <curve type>
),
Default:
None. Must be specified.
Purpose:
This specifies a shared curve or edge between a patch and a trimmed surface,
or two patches, or two trimmed surfaces, for use in world-space texturing.
Patch Data Type | 305
Example:
shared_edge = (
(
type = ULO,
start = ( 0.0
, 0.0247209
end
= ( 0.0
, 5.0
mate_patch = plane,
mate_curve = trim273932360,
mate_type = TRIM
),
(
type = UHI,
start = ( 1.5307337, 0.0029019
end
= ( 1.5307337, 5.0
mate_patch = plane2,
mate_curve = trim273927392,
mate_type = TRIM
)
),
),
),
),
start
Syntax:
start = ( <scalar>, <scalar>),
Range:
Limited by surface’s parametric space
Default:
None. Must be specified if shared_edge on page 304 is specified.
Purpose:
This defines the start of a shared edge for a world-space texture.
Example:
start = (
1.5307337,
306 | Chapter 6 Data types
0.0029019 ),
subdivide
Syntax:
subdivide = uniform
or
subdivide = adaptive
Range:
As enumerated above.
Note: You may also use TRUE (adaptive) or FALSE (uniform).
Default:
uniform
Purpose:
This specifies the type of subdivision algorithm to be used.
Comments:
This component may be animated.
NOTE The interpretation of the divisions and curvature components (described
elsewhere) depend upon the value given to subdivide.
Example:
subdivide = adaptive
trim_region
Syntax:
trim_region = ( cvs = ( <trim_vertex>, <trim_vertex>, … <trim_vertex> ) )
or
trim_region = ( cvs = ( <trim_vertex>, <trim_vertex>, … <trim_vertex> ),
trim_hole = ( <trim_vertex>,
Patch Data Type | 307
<trim_vertex>, …
<trim_vertex> ),
trim_hole = ( <trim_vertex>,
<trim_vertex>, …
<trim_vertex> ),
or trim_region = <trim_vertex_variable>
trim_hole = ( <trim_vertex>,
<trim_vertex>, …
<trim_vertex> ) )
or trim_hole = <trim_vertex_variable>
Range:
Any collection of valid trim_vertices (see Trim_vertex Data Type on page 383).
Default:
None (no trimming to be done).
Purpose:
Defines a trim region.
Comments:
This component may be animated. There may be an arbitrary number of
trim_region components for a patch. The trim_region component uses several
sub-components. The CVs sub-component must be specified, but the trim_hole
on page 309 sub-component is optional. The specification of the CVs is identical
to previous such specifications, but it must use trim_vertex data items. The
trim_hole sub-component is treated separately below.
308 | Chapter 6 Data types
Example:
trim_region =
cvs = (
trim_vertex
trim_vertex
trim_vertex
trim_vertex
trim_vertex
),
(
(0.0, 1.43192,
(0.0, 0.0
,
(1.0, 0.0
,
(1.0, 2.0
,
(0.05547, 1.5,
1),
1),
1),
1),
0)
trim_hole
Syntax:
trim_hole = ( <trim_vertex>,
<trim_vertex>, … <trim_vertex> )
Range:
Any collection of valid trim_vertices (see Trim_vertex Data Type on page 383).
Default:
None (no hole exists).
Purpose:
Defines a hole in a trim region.
Comments:
This component may be animated. There may be an arbitrary number of
trim_hole sub-components for a trim_region on page 307. The specification of
the trim_hole is identical to previous specifications of CVs (except for the fact
that its called trim_hole instead). The actual entries must be Trim_vertex Data
Type on page 383 items.
Example:
trim_hole = (
Patch Data Type | 309
trim_vertex
trim_vertex
trim_vertex
trim_vertex
)
(0.46123, 1.0,
(0.5, 0.91163,
(0.91564, 1.0,
(0.86419, 1.5,
0),
0),
0),
0)
type
Syntax:
type = ( <name>),
Default:
None. Must be specified if shared_edge on page 304 is specified.
Purpose:
This provides the type of edge that is being shared by two surfaces for
world-space texturing.
Example:
type = TRIM,
uclosed
Syntax:
uclosed = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
FALSE (not closed)
Purpose:
Defines whether or not the patch is closed in the u direction.
310 | Chapter 6 Data types
Comments:
This component may be animated.
Example:
uclosed = 0
uknots
Syntax:
uknots = ( <scalar>, <scalar>, …<scalar> )
Range:
Each entry must evaluate to a real number, which must be greater than or
equal to the value of its predecessor.
Default:
None. Must be specified.
Purpose:
This defines the knot vector in the spline’s u direction. It must match with
number of CVs given.
Comments:
It may be animated.
Example:
uknots = ( 0, 1, 2, 3, 4, 5 )
vclosed
Syntax:
vclosed = <scalar>
Patch Data Type | 311
Range:
0 (FALSE) or not 0 (TRUE)
Default:
FALSE (not closed)
Purpose:
Defines whether or not the patch is closed in the v direction.
Comments:
This component may be animated.
Example:
vclosed = 1
vknots
Syntax:
vknots = ( <scalar>, <scalar>, …<scalar> )
Range:
Each entry must evaluate to a real number, which must be greater than or
equal to the value of its predecessor.
Default:
None. Must be specified.
Purpose:
This defines the knot vector in the spline’s v direction. It must match with
number of CVs given.
Comments:
This component may be animated.
312 | Chapter 6 Data types
Example:
vknots = ( -6.2, -5, -5, 0, 2.2, 2.2 )
udegree
Syntax:
udegree = <scalar>
Range:
1 to 33
Default:
none
Purpose:
To describe the degree of the nurbs curve in the u direction for patches. To
define a syntactically correct curve, there must be at least degree + 1 control
vertices.
Comments:
As the degree of the surface increases, it is a good idea to increase the rendering
subdivisions for the object defined with that curve.
Example:
degree = 3
vdegree
Syntax:
vdegree = <scalar>
Range:
1 to 33
Patch Data Type | 313
Default:
none
Purpose:
To describe the degree of the nurbs curve in the v direction for patches. To
define a syntactically correct curve, there must be at least degree + 1 control
vertices.
Comments:
As the degree of the surface increases, it is a good idea to increase the rendering
subdivisions for the object defined with that curve.
Example:
degree = 3
Polyset Data Type
Syntax:
polyset <name> ( <component list> );
Reference:
<name>
Purpose:
A polyset is a polygonal mesh. It may be instanced as an object in the MODEL
Section on page 37. A polyset may be specified as a literal or as a variable. If
specified as a variable, it must have a name. Any of the following components
may be specified between the parentheses:
■
active on page 316
■
casts_shadow on page 317
■
clusters on page 318
■
doublesided on page 319
314 | Chapter 6 Data types
■
light_list on page 320
■
motion_blur on page 321
■
motion_blur_shading_samples on page 321
■
motion_blur_texture_sample_level on page 322
■
norm on page 323
■
opposite on page 323
■
particle_collisions on page 324
■
polygon_areas on page 324
■
polygon on page 325
■
polygons on page 325
■
shader on page 326
■
smooth on page 327
■
st on page 327
■
texture_vertices on page 328
■
vertex_normals on page 328
■
vertices on page 329
Like a patch and a face, all components are specified using a keyword = value
form. Components are separated by commas, and may be in any order. Not
all components are optional. With the exception of the shader component,
if components are specified multiple times, the last specification is used.
Multiple shader components may be present in the polyset definition and be
used by individual polygons. Components not specified take on their default
value.
Polyset Data Type | 315
Example:
polyset Poly_1 (
active = ON,
motion_blur = ON,
smooth = ON,
doublesided = ON,
opposite = OFF,
shader = (DefaultShader ),
shader = (ShaderNumber2 ),
casts_shadow = TRUE,
vertices = ((cv((-11.89838, 4.210732, 0.0), 1)),
(cv((-2.174469, -7.479493, 0.0), 1)),
(cv((-13.28751, -8.289707, 0.0), 1)),
(cv((-2.174469, 6.409883, 0.0), 1)) ),
texture_vertices = (
st( 0.125000, 0.850394 ),
st( 1.000000, 0.055118 ),
st( 0.000000, 0.000000 ),
st( 1.000000, 1.000000 ) ),
vertex_normals = (
norm( 0.000000, 0.000000, 1.000000 ),
norm( 0.000000, 0.000000, 1.000000 ),
norm( 0.000000, 0.000000, 1.000000 ),
norm( 0.000000, 0.000000, 1.000000 ) ),
polygons = (
polygon ((0, 1, 2),(0, 1, 2),(0, 1, 2), 0 ),
polygon ((1, 0, 3),(1, 0, 3),(1, 0, 3), 1 )
)
); /* end of polyset ‘Poly_1’ */
active
Syntax:
active = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
316 | Chapter 6 Data types
Default:
TRUE
Purpose:
A Boolean flag that controls whether the polyset is visible or not.
Comments:
This component may be animated. This is provided so you no longer have to
scale objects in an animation to 0 or translate them outside the scene for
frames in which they shouldn’t appear.
Example:
active = FALSE
casts_shadow
Syntax:
casts_shadow = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Purpose:
A boolean that controls whether or not this polyset will cast a shadow.
Comments:
This component may be animated.
NOTE A surface with transparent or semi-transparent shading will not cast a
shadow when RayCasting.
Polyset Data Type | 317
Example:
casts_shadow = FALSE
clusters
Syntax:
clusters = (<cluster matrix list>),
Range:
N/A
Default:
None.
Purpose:
A list of cluster matrices that affect the current surface.
Comments:
A cluster matrix describes the initial position of the matrix (4X4 scalars), the
type of cluster effect (JOINT or LEAF), JOINT level (or 0 if the type is LEAF),
and translate, rotate, scale as 3 scalar tuples.
318 | Chapter 6 Data types
Example:
clusters = (
clm( CL_r_peak,
1.0
, 0.0
, 0.0
,
0.0
, 1.0
, 0.0
,
0.0
, 0.0
, 1.0
,
0.283681 , 0.0285822, -0.5841172,
LEAF, 0,
0.0
, 0.0
, 0.0
,
0.0
, 0.0
, 0.0
,
1.0
, 1.0
, 1.0
),
clm( CL_knot45_section0_Rwrist,
1.0
, 0.0
, 0.0
,
0.0
, 1.0
, 0.0
,
0.0
, 0.0
, 1.0
,
0.283681 , 0.0285822, -0.5841172,
LEAF, 0,
0.0
, 0.0
, 0.0
,
0.0
, 0.0
, 0.0
,
1.0
, 1.0
, 1.0
)
clm( CL_cluster#10,
1.0
, 0.0
, 0.0
,
0.0
, 1.0
, 0.0
,
0.0
, 0.0
, 1.0
,
0.283681 , 0.0285822, -0.5841172,
JOINT, 3,
-0.2398842, -0.0303474, 0.0
,
0.0
, 0.0
, 0.0
,
1.0
, 1.0
, 1.0
)
0.0
0.0
0.0
1.0
,
,
,
,
0.0
0.0
0.0
1.0
,
,
,
,
0.0
0.0
0.0
1.0
,
,
,
,
),
doublesided
Syntax:
doublesided = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Polyset Data Type | 319
Default:
TRUE; that is, the patch will be doublesided.
Purpose:
The scalar will be interpreted as a Boolean, with 0 being FALSE and any other
value TRUE. If doublesided is FALSE, rendering proceeds more quickly, but
only one side of the surface is rendered. For most objects other than closed
surfaces, doublesided = TRUE is desirable. The reader is warned that with the
raytracer, rays may strike the object from any direction.
Comments:
This component may be animated.
Example:
doublesided = FALSE
light_list
Syntax:
light_list = ( <light>, <light>, … <light> )
Range:
Each light given must have been defined; literals may not be used.
Default:
See below.
Purpose:
Each item referenced must be the name of a previously declared light data
item, or an array element of type light (see the Light Data Type on page 186
for more information). Literals may not be used. This lists the lights to be used
by this polyset. If light_list is omitted or if it is specified and is empty, all
nonexclusive lights are used to illuminate the polyset. If light_list is specified,
and the list contains defined lights, then all instances of those lights in the
scene, and only those, will be used for this polyset. This enables situations
320 | Chapter 6 Data types
where you may want 10 lights on a particular object, for example, but only
two lights on the rest of the scene.
Comments:
This component may not be animated.
Example:
light_list = ( spot01, spot02, flood, globallight )
motion_blur
Syntax:
motion_blur = <scalar>
Default:
ON
Range:
0 (OFF) or non-zero (ON)
Purpose:
If motion_blur_on on page 74 is set for the file, this flag indicates that motion
blur should be calculated for this object.
Example:
motion_blur = ON
motion_blur_shading_samples
Syntax:
motion_blur_shading_samples = <scalar>
Default:
3 - for bump or displacement mapped objects
Polyset Data Type | 321
1 - for all other objects
Range:
>= 3 for bump or displacement mapped objects
> 0 for all other objects
Purpose:
If motion_blur_on on page 74 is set for the file, this flag indicates the number
of samples done for shading of motion-blurred objects.
Example:
motion_blur_shading_samples = 1
motion_blur_texture_sample_level
Syntax:
motion_blur_texture_sample_level = <scalar>
Default:
3
Range:
0-5
Purpose:
If motion_blur_on on page 74 is set for the file, this flag indicates the level of
sampling done for texturing of motion-blurred objects. A 0 indicates no extra
samples (lowest quality) and 5 means highest quality motion-blurred textures.
Note, this flag does not apply to bump or displacement mapping.
Example:
motion_blur_texture_samples = 3
322 | Chapter 6 Data types
norm
Syntax:
norm( <scalar>, <scalar>, <scalar> )
Purpose:
Part of a polyset vertex normal list. The 'norm()' specifies the vertex normal
coordinate.
Example:
norm( 0.000000, 0.000000, 1.000000 )
opposite
Syntax:
opposite = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
FALSE
Purpose:
To reverse the sense of direction of the normal for the polyset.
Comments:
This component may be animated. If doublesided on page 319 is FALSE (for
example, for faster execution), opposite can be used to reverse the orientation
of the backfacing and frontfacing parts of the polyset. This may be done in
order to correct potential visibility problems.
Example:
opposite = TRUE
Polyset Data Type | 323
particle_collisions
Syntax:
particle_collisions = BOUNDING_BOX_COLLISIONS | OFF |
GEOMETRY_COLLISIONS
Range:
As above
Default:
OFF
Purpose:
To define which objects collide with particles.
Example:
particle_collisions = BOUNDING_BOX_COLLISIONS
polygon_areas
Syntax:
polygon_areas = ( <scalar>, ... <scalar>)
Default:
none
Purpose:
A list of areas, one per polygon, to be used in particle emission calculations.
Comments:
This component may not be animated. As particle emission rates depend on
the area of a polygon, the area list component allows the initial areas of
polygons to be set and made constant. The area list is indexed by the polygon
number, so that polygon 0 in the polyset would use the first element of the
area list.
324 | Chapter 6 Data types
Example:
polygon_areas = ( 0.2, 0.3, 2.4 )
polygon
Syntax:
polygon( (<integer>, <integer>, <integer>), [(<integer>, <integer>, <integer>),]
[(<integer>, <integer>, <integer>)] [, <integer>])
Purpose:
Part of a polyset declaration. The integers represent indexes into the vertex,
texture vertices, and vertex normals arrays that must accompany a polyset
declaration. Additionally, the last parameter indicates which shader of those
specified in the shader declarations should be used for this polygon.
Example:
polygon ((0, 1, 2),(3, 4, 5),(6, 7, 8), 0 )
The above example indicates that the polygon should use vertices number 0,
1, and 2 for position, texture vertices number 3, 4, and 5 for texture
coordinates, and vertex normals 6, 7, and 8 for normals.
The trailing 0 indicates that the first shader declared in the polyset should be
used to shade the polygon.
Note that the texture vertex and vertex normal data is optional. If the texture
vertex information is not specified then 0, 0 will be used as texture coordinates.
If the vertex normal data is not specified (and the vertex_normals list is not
specified in the polyset), then the normals will be computed prior to rendering.
polygons
Syntax:
polygons = ( <polygon>, <polygon>, ... <polygon )
Range:
Any list of valid polygons.
Polyset Data Type | 325
Default:
None. Must be specified.
Purpose:
To describe the connectivity of previously declared vertices in the polyset.
Example:
polygons = (
polygon ((0, 1, 2), (0, 1, 2), (0, 1, 2), 0)
polygon ((1, 3, 4), (1, 3, 4), (1, 3, 4), 1)
)
shader
Syntax:
shader = (<shader>)
or
shader = ( <shader>, <shader>, … <shader> )
Range:
The shaders given may be variables or array elements of type shader (see Shader
Data Type on page 331 for more information). Note that there is no such thing
as a literal shader.
Default:
None. Must be specified.
Purpose:
This specifies which shading characteristics are assigned to the surface.
Comments:
This component may be animated. If a list of shaders is specified, they will
be visible in the order given.
326 | Chapter 6 Data types
Note also that multiple occurrences of the shader component may occur in a
polyset definition. This allows multiple shaders to be assigned to the polyset.
The shader used for any given polygon is specified as part of the polygon
definition.
Example:
shader = (pink)
shader = (blue)
smooth
Syntax:
smooth = <scalar>
Range:
0 (OFF) or not 0 (ON)
Default:
ON
Purpose:
To enable the user to smooth or flat shade a polyset.
This component is animatable.
Example:
smooth = ON
st
Syntax:
st( <scalar>, <scalar> )
Purpose:
Part of a polyset texture vertex list. The 'st()' specifies the texture coordinate.
Polyset Data Type | 327
Example:
st( 0.34, 0.322 )
texture_vertices
Syntax:
texture_vertices = ( <st>, ... [<st>] )
Range:
Any collection of valid polyset texture vertices.
Default:
None. Must be specified.
Purpose:
Defines the texture vertex array for the polyset. The first texture vertex
encountered is considered texture vertex 0 for the purposes of the polygon
indices later in a polyset declaration, the second texture vertex encountered
is considered vertex 1, and so on..
Comments:
This component must be specified before the 'polygons on page 325'
component.
Example:
texture_vertices = (
st( 0.125000, 0.850394
st( 1.000000, 0.055118
st( 0.000000, 0.000000
st( 1.000000, 1.000000
),
),
),
) ),
vertex_normals
Syntax:
vertex_normals = ( <normal>, [<normal>] )
328 | Chapter 6 Data types
Range:
Any collection of valid polyset vertex normals.
Default:
None. Must be specified.
Purpose:
Defines the vertex normal array for the polyset. The first vertex normal
encountered is considered vertex normal 0 for the purposes of the polygon
indices later in a polyset declaration, the second vertex normal encountered
is considered vertex normal1, and so on..
Comments:
This component must be specified before the 'polygons on page 325'
component.
Example:
vertex_normals = (
norm( 0.000000, 0.000000, 1.000000 ),
norm( 0.000000, 0.000000, 1.000000 ),
norm( 0.000000, 0.000000, 1.000000 ),
norm( 0.000000, 0.000000, 1.000000 ) ),
vertices
Syntax:
vertices = ( (<cv> [, <st>] [, <norm>]), (<cv> [, <st>] [, <norm>]), ... (<cv> [,
<st>] [, <norm>]) )
Range:
Any collection of valid polyset vertices.
Default:
None. Must be specified.
Polyset Data Type | 329
Purpose:
Defines the vertex array for the polyset. The first vertex encountered is
considered vertex 0 for the purposes of the polygon indices later in a polyset
declaration, the second vertex encountered is considered vertex 1, and so on.
In version 7, it is now also possible to write the vertex normals and texture
coordinates in separate lists of items, and index them separately by polygons.
Because of this, AliasStudio no longer places texture coordinates in the vertex
definitions, though compatibility is maintained for older SDL files using this
format.
Comments:
This component must be specified before the 'polygons' component. The <cv>s
and <st>s are implicitly paired by the syntax, and this pairing is maintained.
Example:
vertices = ((cv((-11.89838, 4.210732, 0.0), 1)),
(cv((-2.174469, -7.479493, 0.0), 1)),
(cv((-13.28751, -8.289707, 0.0), 1)),
(cv((-2.174469, 6.409883, 0.0), 1)) ),
The equivalent of this example with vertex normals and texture coordinates
is:
vertices = ((cv(( 0.0 , -0.5 , 0.0 ),
norm (1.0, 0.0, 0.0)), etc...
Scalar Data Type
Declaration:
scalar <name> ( <expression> );
Reference:
<name>
Literal:
( <expression> )
330 | Chapter 6 Data types
1.0 ), st( 0.0 , 0.0 ),
or
<expression>
Purpose:
A scalar may be specified as a literal or as a variable. If specified as a variable,
it must have a name. The only component of a scalar is its value.
Example:
scalar switch(OFF);
NOTE In version 7, to allow for faster processing and reduced SDL file sizes,
animation curves that exhibit constant values will be written out as scalar values,
not animation curves.
Shader Data Type
Declaration:
shader <name> ( procedure=<procedure name>, <component list> ) ;
Reference:
<name>
Purpose:
This defines a shader. A shader may only be specified as a variable, thus a
name is always required. Any of the following components may be specified
between the parentheses. Please note that particle system components are
described in the section following the Light Data Type.
■
bump on page 335
■
color on page 336
■
diffuse on page 337
■
displacement on page 337
■
eccentricity on page 338
Shader Data Type | 331
■
fill_color on page 339
■
glow_intensity on page 339
■
glow_rotation on page 340
■
hide_glow_source on page 341
■
incandescence on page 342
■
matte_fraction on page 342
■
model on page 343
■
opacity_depth on page 345
■
psys_bend_u on page 257
■
psys_bend_v on page 257
■
psys_blob_lighting on page 258
■
psys_blob_map on page 259
■
psys_blob_noise on page 260
■
psys_blob_noise_frequency on page 260
■
psys_blob_threshold on page 261
■
psys_blur_quality on page 261
■
psys_branch_angle on page 262
■
psys_buoyancy on page 262
■
psys_collisions on page 263
■
psys_color on page 264
■
psys_curl on page 264
■
psys_density on page 265
■
psys_elasticity on page 266
■
psys_emission on page 266
■
psys_end_frame on page 267
■
psys_filename on page 267
■
psys_friction on page 268
332 | Chapter 6 Data types
■
psys_glow_intensity on page 268
■
psys_hair_length_max on page 269
■
psys_hair_length_min on page 269
■
psys_hair_stiffness on page 270
■
psys_hair_segments on page 271
■
psys_hit_method on page 271
■
psys_incandescence on page 272
■
psys_lifespan_min on page 273
■
psys_lifespan_max on page 273
■
psys_mass on page 274
■
psys_motion_type on page 275
■
psys_num_children on page 275
■
psys_parent_shading on page 276
■
psys_particles_per_sec on page 276
■
psys_randomization on page 277
■
psys_render_type on page 277
■
psys_size on page 278
■
psys_speed on page 279
■
psys_speed_decay on page 280
■
psys_speed_range on page 280
■
psys_split_time on page 281
■
psys_start_frame on page 281
■
psys_surface_shading on page 282
■
psys_time_random on page 283
■
psys_translucence on page 284
■
psys_transparency on page 284
■
psys_use_particle_file on page 285
Shader Data Type | 333
■
reflect_background on page 346
■
reflection on page 346
■
reflection_limit on page 347
■
reflectivity on page 348
■
refraction_jitter on page 349
■
refraction_limit on page 349
■
refraction_samples on page 350
■
refractive_index on page 351
■
respect_reflection_map on page 351
■
shading_map on page 352
■
shadow_level_limit on page 353
■
shinyness on page 354
■
specular on page 354
■
specular_rolloff on page 355
■
split_velocity_min on page 356
■
surface_width on page 356
■
translucence on page 357
■
translucence_depth on page 358
■
transparency on page 359
■
transparency_shade on page 360
■
u_patch_lines on page 361
■
use_background_color on page 362
■
use_fill_color on page 362
■
v_patch_lines on page 363
334 | Chapter 6 Data types
Comments:
All components are specified using a keyword=value form. Components are
separated by commas. Not all components are optional. The components may
be specified in any order. Components that are not specified take on their
default value. If any component is specified more than once, the last such
specification will be used, and all previous ones ignored. If all are omitted,
the defaults will result in a shader with the same properties as the interactive
package default shader. Not all components are meaningful in all
combinations. In situations where a component is not meaningful, any
specification of it will be ignored with no ill effect.
Note that shaders cannot be used as literals.
Example:
shader arrow ( model
= phong,
specular = (0.853881, 0.853881, 0.853881),
shinyness = 23.0,
color = (255.0, 0.0, 33.0)
);
bump
Syntax:
bump = texture <texture>
Range:
Not meaningful.
Default:
none.
Purpose:
The surface normal is perturbed according to the value given by the texture.
Bump mapping makes a surface appear bumpy or rough by affecting the surface
normal at a point and not by moving the actual surface. Therefore, the
silhouette of the object will appear the same as it did before the bump map
was applied. The scale of bumps is set by the amult on page 366 and aoffset on
page 366 statements.
Shader Data Type | 335
Comments:
This component may be animated. bump is appropriate for all shading models.
Example:
bump = noisy
color
Syntax:
color = <triple>
or
color = texture <texture>
Range:
Each component of a triple must be in the range 0 to 255.
Default:
( 0.0, 150.0, 255.0 )
Purpose:
If color = <triple>, the three components of the triple are the red, green and
blue aspects of the color. If color = texture <texture>, then the texture is
mapped onto the surface. A color is appropriate for all shading models. For
more information on textures, see Texture Data Type on page 364.
Comments:
This component may be animated. Note that the default has been changed
to agree with the interactive package.
Example:
color = (255.0, 0.0, 33.0)
336 | Chapter 6 Data types
diffuse
Syntax:
diffuse = <scalar>
Range:
Not checked; useful range is 0.0 to 1.0. While 0.0 to 1.0 provides a realistic
range, numbers greater than 1 can be used: the effect is that more illumination
is scattered by the object than was received by it.
Default:
0.8
Purpose:
The scalar determines the amount of illumination reflected by a matte surface,
affecting the surface’s brightness. A high diffuse setting produces a broad range
of shade on the object. A setting of 0.0 produces virtually no response to lights,
while 1.0 produces very abrupt changes in shading, as found on acrylic or
Plexiglass.
A diffuse component is appropriate for the lambert, phong, and blinn shading
model on page 343s. It is ignored for the lightsource model.
Comments:
This component may be animated.
Example:
diffuse = 0.99
displacement
Syntax:
displacement = texture <texture>
Range:
Not meaningful.
Shader Data Type | 337
Default:
none.
Purpose:
The rendered surface is displaced along the surface normal according to the
value given by the texture. With displacement maps, the silhouette is
consistent with the rest of the surface, unlike bump on page 335 maps.
Comments:
This component may be animated. displacement is appropriate for all shading
models.
Example:
displacement = noisy
eccentricity
Syntax:
eccentricity = <scalar>
Range:
Any value other than 1.0
Default:
0.3
Purpose:
This is used only with the blinn shading model on page 343. It sets the size of
the object’s highlight in a manner similar to the shinyness on page 354
statement. This value controls the variance in the angle of the microfacets of
the surface.
The eccentricity component should be specified for the blinn shading model.
An eccentricity value of 0.0 is acceptable.
338 | Chapter 6 Data types
Comments:
This component may be animated.
Example:
eccentricity = 0.75
fill_color
Syntax:
fill_color= <triple>
Range:
Each component of a triple must be in the range 0 to 255.
Default:
(255, 255, 255)
Purpose:
Fill_color is only relevant in hidden-line rendering, and when use_fill_color
on page 362 is turned on. The fill color defines the interior color of the surface
not covered by the outline of the surface.
Example:
fill_color= (255, 255, 255)
glow_intensity
Syntax:
glow_intensity = <scalar>
Range:
Non-negative
Shader Data Type | 339
Default:
0.0
Purpose:
This simulates the effect when light intensity exceeds the range of the recording
medium (e.g. film or a retina) causing light to bleed across the medium. Do
to the limited contrast range of video and even film. it is impossible for
something to appear very bright if it does not have a glowing halo. The glow
fools our eyes into believing that the light is brighter than it really is.
Comments:
The glow intensity scales the intensity of a shaded pixel before it is passed
into the post process glow pass. This intensity can not be greater than
(255,255,255). For very bright glows, the glow and halo color parameters in
the ENVIRONMENT Section on page 99 should be set high. Note that most
of the parameters controlling shader glow are on the Environment.
Components of shading (such as specular highlights or texture mapped dots)
can be made to glow by using the threshold parameter on the Environment.
This component may be animated.
Example:
glow_intensity = .5
glow_rotation
Syntax:
glow_rotation = <scalar> (in degrees)
Range:
-infinity to infinity
Default:
0.0
340 | Chapter 6 Data types
Purpose:
To rotate the various glow and fog noise and star effects about the location
of the shader.
Comments:
Affects glow_star_level on page 220, and glow_radial_noise on page 218.
Example:
glow_rotation = 45.0
hide_glow_source
Syntax:
hide_glow_source= <boolean>
Range:
ON or OFF.
Default:
OFF
Purpose:
This allows an object to be used as a source of glow without the object
appearing in the final render: if this is ON then only the glow effect itself will
appear. This is very useful when creating glowing gas like effects.
Comments:
If the glow_intensity on page 216 is zero, hide_glow_source has no effect.
This component may be animated.
Example:
hide_glow_source = ON
Shader Data Type | 341
incandescence
Syntax:
incandescence = <triple>
or
incandescence = texture <texture>
Range:
Each component of the triple must be in the range 0 to 255.
Default:
( 0.0, 0.0, 0.0 )
Purpose:
incandescence can be used for surfaces that appear to radiate energy, such as
light bulbs and fire, and in moderate amounts for foliage. The value of
incandescence is added to the color of the model. The effect is as if the model
were glowing or radiating energy. incandescence is appropriate for all shading
models.
Comments:
This component may be animated.
Example:
incandescence = (255.0, 0.0, 33.0)
matte_fraction
Syntax:
matte_fraction = <float>
Range:
0 to 1.
342 | Chapter 6 Data types
Default:
0.0
Purpose:
matte_fraction is only relevant when mask on page 154 files are written during
rendering. For each alpha value, (1-matte_fraction) is multiplied to it to arrive
at the actual alpha value written to file. This allows for opaque objects to not
register an alpha, or allow an object (after compositing) to slowly become
visible as you animate the matte_fraction from 1 to 0.
Comments:
This component may be animated.
Example:
matte_fraction = 0.0
model
Syntax:
Either : model = blinn
or: model = lambert
or: model = lightsource
or: model = phong
Range:
As enumerated above.
Default:
lambert
Shader Data Type | 343
Purpose:
Sets the shading model used for rendering. The models are listed below in the
order of their increasing sophistication and time required to render.
lightsource
This is a simple model that only uses the
color on page 336 of the shader, and the
color and intensity of all lights illuminating
it. It is independent of the camera position
and the light positions.Therefore it is appropriate when creating surfaces that should
look uniform. Note, however, that it only
makes such surfaces appear luminous; they
do not, in fact, illuminate anything. If the
lightsource shading model is selected, then
the rendered color will be the same as the
shader color. There is no shading, and
lights are ignored.
lambert
In this model, matte shading is produced
by only using the color on page 336 and
diffuse on page 337 components (to follow).
The light positions are used, but not the
camera’s position.
phong
This model produces shading with highlights. It uses the color on page 336, diffuse
on page 337, shinyness on page 354 and
specular on page 354 components (to follow). The contribution of each light depends on its position, the surface’s orientation, and the eye’s position.
blinn
This model produces shading with larger
highlights than those occurring in the
phong model, especially when illumination
strikes the surface at a grazing angle. This
also produces soft highlights that tend to
be more realistic than the phong model.
It uses the color on page 336, diffuse on
page 337, specular on page 354, eccentricity
344 | Chapter 6 Data types
on page 338 and refractive_index on page
351 components (to follow).
Comments:
This component may not be animated.
Example:
model = phong
opacity_depth
Syntax:
opacity_depth = <scalar>
Range:
Any floating point number.
Default:
0.0
Purpose:
Opacity depth causes transparency of an object to diminish with the thickness
of an object. This is useful when creating hair, fur, and cloud effects. Objects
will be fully opaque where their depth is greater than the opacity_depth. Note
that when the opacity depth is zero, it has no effect (as opposed to making
an object always opaque).
Comments:
The shader must have some transparency to view this effect. When
opacity_depth is non-zero then transparency will modulate specularity,
reflectivity, and incandescence, which are normally independent of
transparency. This makes it easier to create soft fuzzy objects. Also, if you want
to transparency map holes in a surface that has specular highlights, set the
opacity_depth to a high value, instead of creating a matching specular map.
Shader Data Type | 345
Transparent objects will cast shadows in the raycaster if their opacity depth
is non-zero.
Example:
opacity_depth = 0.2
reflect_background
Syntax:
reflect_background = <scalar>
Range:
0 (OFF) or not 0 (ON).
Default:
OFF.
Purpose:
If the background has an environment map, then reflect_background = ON
will reflect this environment.
Comments:
reflect_background overrides reflection mapping on the shader. It also overrides
reflected rays in the RayTracer.
Example:
reflect_background = ON
reflection
Syntax:
reflection = texture <texture>
Range:
Not meaningful.
346 | Chapter 6 Data types
Default:
None (no reflection).
Purpose:
This provides a environment map for the current shader.
Comments:
This component may be animated. A reflection is appropriate for phong and
blinn shading model on page 343s.
Example:
reflection = room
reflection_limit
Syntax:
reflection_limit = <scalar>
Range:
Non-negative. If a negative number is given, zero will be used.
Default:
1
Purpose:
Ray tracing is a recursive process. Each ray bounces off of reflective objects. If
the user places two reflective objects parallel to each other and places the eye
point between them, then it is easy to imagine a ray bouncing back and forth
between these mirrors forever. This is undesirable. The user can control the
number of bounces a ray may take on a per shader basis with the
reflection_limit component.
Comments:
This component may be animated.
Shader Data Type | 347
Example:
reflection_limit = 0
Let us assume that an object uses a shader with this component. During the
ray tracing process, a primary ray (which has a level of 0 by definition) hits
this object. The reflectivity is calculated, and we prepare to trace a ray in the
reflected direction. The reflection_limit is compared against the level of the
incident ray. The reflected ray will be traced only if the reflection_limit is
greater than the incident ray’s level. For the example this is false; the incident
ray’s level is 0 and the reflection_limit is also 0. Therefore, no reflected ray is
traced.
reflectivity
Syntax:
reflectivity = <scalar>
or
reflectivity = texture <texture>
Range:
unbounded, but meaningful range is 0.0 to 1.0
Default:
1.0
Purpose:
This scale factor is multiplied by the value produced by a reflection map. It
allows the user to control the reflection map’s contribution to the final value
of the shader. It is ignored if there is no reflection.
The reflectivity component is appropriate for the phong and blinn shading
model on page 343s. It is ignored for lightsource and lambert models. Also note
that the reflection will be multiplied by specular on page 354, just like a
highlight.
Comments:
This component may be animated.
348 | Chapter 6 Data types
Example:
reflectivity = 0.9
refraction_jitter
Syntax:
refraction_jitter= <scalar>
Range:
Between 0 and 1.
Default:
0
Purpose:
Refraction_jitter is valid for raytracing of transparent surfaces only. It jitters
the refraction index for refraction rays. This can produce effects such as frosted
glass. However, note that aliasing artifacts may arise when not enough
refraction_samples are taken.
Example:
refraction_jitter= 0.1
refraction_limit
Syntax:
refraction_limit = <scalar>
Range:
Non-negative. If a negative number is given, zero will be used.
Default:
1
Shader Data Type | 349
Purpose:
This controls the propagation of refracted rays through transparent objects.
It is similar in intent and behavior to reflection_limit on page 347, but for
refracted rays. It is only appropriate for RayTracing, and is ignored for all other
modes of rendering.
Comments:
This component may be animated.
Example:
refraction_limit = 3
refraction_samples
Syntax:
refraction_samples= <scalar>
Range:
Any value greater than 1.
Default:
0
Purpose:
Refraction_samples defines the number of refraction rays to shoot when
transparent surfaces are hit in ray tracing. This can achieve the effect of fuzzy
refractions, and will also anti-alias refraction_jitter artifacts. Note that with a
larger value specified for this parameter, the longer the ray tracing time.
Example:
refraction_samples= 1.1
350 | Chapter 6 Data types
refractive_index
Syntax:
refractive_index = <scalar>
Range:
Must be greater than 0.0; no maximum, but practical limit is 3.0.
Default:
1.3
Purpose:
This controls the angles of refracted rays through transparent objects. It is
only appropriate for RayTracing, and is ignored for all other modes of
rendering.
Example:
refractive_index = 3,
respect_reflection_map
Syntax:
respect_reflection_map = <scalar>
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Purpose:
This controls the use of a reflection map. RayTracing will reflect the
environment of an object without having to create a cubic or spherical
reflection map (see Creating Rendered Cubic Environment Maps on page 487
for more information on creating cubic reflection maps). There are times,
Shader Data Type | 351
however, that a user may want to use a reflection map rather than trace the
reflected rays. For example, reflective pillars behind a complex car model are
required to reflect the image of the car. RayTracing the reflections is expensive
because of the sheer volume of geometry describing the car. Since the pillars
are not the main focus of the rendering, the reflections on the pillars need
not be all that accurate. Therefore, a reflection map may be used for the pillars
with little quality degradation. Setting respect_reflection_map to TRUE will
accomplish that. If this component is true, no reflection rays will be generated
and any reflection map will applied. If respect_reflection_map is false and the
rendering mode is raytrace, any reflection map will be ignored and reflection
rays generated up to the relevant recursion limit. Note that this is only
appropriate when RayTracing. Reflection maps are always applied when
RayCasting.
Comments:
This component may be animated.
Example:
respect_reflection_map = FALSE
shading_map
Syntax:
shading_map= <triple>
or
shading_map= texture <texture>
Range:
Each component of a triple must be in the range 0 to 255.
Default:
( 0.0, 0.0, 0.0 )
Purpose:
If color = <triple>, the three components of the triple are the red, green and
blue aspects of the color. If shading_map= texture <texture>, then u value of
352 | Chapter 6 Data types
the texture is mapped to the shader’s hue, and the v value is mapped to the
shader’s intensity. A color is appropriate for all shading models.
Comments:
This component may be animated. Note that the default has been changed
to agree with the interactive package.
Example:
shading_map= (255.0, 0.0, 33.0)
shadow_level_limit
Syntax:
shadow_level_limit = <scalar>
Range:
-1 to infinity
Default:
1
Purpose:
This controls the propagation of shadow rays. It is similar in intent and
behavior to reflection_limit on page 347, but for shadow rays. Shadow rays are
generated towards all light sources with shadow on page 234 = TRUE. Shadow
rays are defined to be of the same level as the incident ray. Therefore, setting
shadow_level_limit = 1; will cause shadow rays to be traced from intersections
generated by level 0 or level 1 rays. If a level 2 (or higher) ray strikes a object,
no shadow rays will be traced, and the lighting will be calculated directly
without shadowing. The shadow_level_limit component is only appropriate
for RayTracing, and is ignored for all other modes of rendering.
Comments:
This component may be animated.
Shader Data Type | 353
Example:
shadow_level_limit = 20
shinyness
Syntax:
shinyness = <scalar>
Range:
Must be greater than zero. Useful range is 2.0 to 200.0
Default:
20.0
Purpose:
This is used only with the phong shading model. The scalar determines the
size of an object’s spot of reflection. The higher the value of the shinyness
component, the smoother the surface looks. A shinyness component should
be specified for the phong model on page 343.
Comments:
This component may be animated.
Example:
shinyness = 8
specular
Syntax:
specular = <triple>
or
specular = texture <texture>
354 | Chapter 6 Data types
Range:
Not checked; useful range is 0.0 to 1.0 for each of red, green and blue.
Default:
( 0.0, 0.0, 0.0 )
Purpose:
If specular = texture <texture>, the highlights across a surface can be made to
vary. This requires a 24-bit map. If an 8-bit map is specified, a 24-bit greyscale
map will be generated on the fly. You might use a texture here for such optical
effects as gas on water or other iridescent effects. The triple is used as a
multiplying factor for the red, green and blue aspects of the specular highlight.
The multiplying factor affects the hue and the hotness or brightness of the
specular highlight.
A specular component is appropriate for the phong and blinn shading model
on page 343s. It is ignored for lightsource and lambert models.
Comments:
This component may be animated. Note that the specular component affects
reflected images (reflection maps) as well as highlights.
Example:
specular = (0.3, 0.4, 0.5)
specular_rolloff
Syntax:
specular_rolloff = <scalar>
Range:
Not checked; useful range is 0.0 to 1.0; absolute range is -infinity to infinity.
Default:
0.3
Shader Data Type | 355
Purpose:
Controls the effect where some surfaces are more reflective at oblique angles.
specular_rolloff has a range of 0.000 through 1.000. Rolloff values around
0.700 will create a “wet” look on a surface. specular_rolloff is only applicable
to blinn model on page 343 surfaces.
Also affects reflected rays in reflection maps.
Example:
specular_rolloff = 0.3,
split_velocity_min
Syntax:
split_velocity_min = <scalar>
Range:
0 to infinity
Default:
5
Purpose:
Appears only if psys_collisions on page 263 are set to ON. This provides a limit
on the speed a particle must be moving when it collides with an object to
determine if the particle splits.
Example:
split_velocity_min = 5
surface_width
Syntax:
surface_width= <scalar>
356 | Chapter 6 Data types
Range:
Any value greater than 0.
Default:
0.0
Purpose:
Surface_width is only relevant in RayTracing for transparent surfaces. When
the value is set to 0, the transparent surface is considered to be a solid. Thus
refraction rays bend through this new medium in the interior of the surface.
If a non-zero surface_width is specified, then the surface is not considered a
solid, but rather the refraction rays bend through this new medium only for
this surface width.
This is a fast method using RayTracing. Artifacts may appear if unreasonable
surface_width values are specified (i.e. the surface width is actually larger than
the surface itself).
Example:
surface_width= 0.3,
translucence
Syntax:
translucence = <scalar>
Range:
Any floating point number.
Default:
0.0
Purpose:
This simulates the way light diffusely penetrates through translucent objects.
It is very useful for a wide range of materials: clouds, fur, hair, marble, jade,
wax, paper, leaves, petals, frosted light bulbs. The translucence_depth
Shader Data Type | 357
determines the distanced light will penetrate into the object. If the translucence
depth is greater than zero, then light can shine on surfaces that face away
from the lightsource. For example, a spotlight with a texture map could act
like a rear projector lighting up a translucent screen from behind. If the light
casts shadows, then the translucence depth will determine how far the light
can penetrate into the object.
Objects like fur and hair benefit greatly by shading the translucency and very
little diffuse illumination. The effect is that small scale surface bumps and
tufts have very soft shading as light readily passes through, while large scale
features (like the back of the object, as opposed to the front) get full shadows
and highlights. This effect is almost impossible to achieve without translucence.
Comments:
Note that for lights without shadowing, the translucence_depth on page 358
is effectively zero or infinite (all non-zero values). For raycast shadows, a faint
gridlike artifact is sometimes visible. Usually this can be fixed by increasing
the shadow quality or lowering the shadow resolution.
Generally it is useful to lower the diffuse on page 337 intensity value when the
translucence is high, to avoid washout.
The translucence calculation is based on illumination from lights, and has
nothing to do with an object’s transparency; however, as an object becomes
more transparent, the translucent (as well as diffuse) illumination gets dimmer.
Ambient lights have no effect on translucent (or diffuse) illumination.
This parameter may be animated.
Example:
translucence = 0.5
translucence_depth
Syntax:
translucence_depth = <scalar>
Range:
Any floating point number.
358 | Chapter 6 Data types
Default:
0.5
Purpose:
This determines how far light can translucently penetrate through an object.
See translucence on page 357 for more information.
Comments:
Note that for lights without shadowing the translucence_depth is effectively
zero or infinite (all non-zero values). In the raycaster, for very shallow depths
(for example, 0.1) the spotlight parameter shadow_min_depth on page 239
should be small (0.01) and the shadow_blend_offset on page 238 should also
be small (0.2).
This parameter may be animated.
Example:
translucence_depth = 0.2
transparency
Syntax:
transparency = <triple>
or
transparency = texture <texture>
Range:
0 to 255
Default:
0,0,0
Purpose:
Transparency is a three channel value. Any color can be specified as the
transparency of a shader, white (255,255,255) being totally transparent and
Shader Data Type | 359
black (0,0,0) being totally opaque. Colors are filtered as you would expect; a
white object behind a green transparent object will appear green (the red and
blue having been filtered out), or a red object behind a blue transparent object
will appear black.
If transparency is assigned a texture, the transparency across a surface can
range from opaque to transparent depending on the value of the texture at
any point. If an 8 bit map is specified, the value of the map is repeated to
make a color value; a value of 35 in the 8 bit map will become (35, 35, 35).
Note that highlights and reflections on very transparent objects will not be
washed away. Transparency is appropriate for all shading models.
Comments:
This component may be animated.
Example:
transparency = (255, 255, 255)
transparency_shade
Syntax:
transparency_shade = <scalar>
Range:
0 to 1. If a number smaller than 0 is used, transparency_shade is forced to 0;
for numbers greater than 1, transparency_shade is forced to 1.
Default:
0
Purpose:
Light is not equally shadowed when it passes through a transparent object: it
is focused, creating illumination that is brighter at some points and darker at
others. To produce this effect properly requires a special ray trace from the
point of view of the light source, and it is expensive. In order to approximate
this type of effect cheaply, we use a technique similar to the ambient light
model. That is, light which passes nearly tangentially through a transparent
360 | Chapter 6 Data types
object will be attenuated more than light passing nearly perpendicularly
through it. This is controlled in the same manner as the ambience component
of an ambient light, but as part of the shader which is applied to the object.
Comments:
This component may be animated.
Example:
transparency_shade = 0
This results in a constant attenuation of the light through the object. With
the default setting, planar transparent objects will cast a nearly uniform shadow
unless a light source is close to the object.
u_patch_lines
Syntax:
u_patch_lines= <scalar>
Range:
Any value greater than 0.
Default:
0
Purpose:
U_patch_lines is only relevant in hidden-line rendering. By default, only the
outline of the surface is drawn in hidden-line rendering (i.e. when
u_patch_lines = 0). However, it is possible to get a gridded look of the outline,
in which a number of lines per isoparm can be drawn through the u-direction
of the surface. This number is the setting for u_patch_lines.
Because the gridded lines are drawn according to the uv-parameterization of
the surface, it can warp undesirably. If such a case occurs, the best solution
would be turn chord_length on in the texture definition.
Example:
u_patch_lines = 0
Shader Data Type | 361
use_background_color
Syntax:
use_background_color = <scalar>
Range:
0 (OFF) to 1 (ON). If a number smaller than 0 is used, use_background_color
is forced to 0; for numbers greater than 1, use_background_color is forced to
1.
Default:
0
Purpose:
For use_background_color, the color value for the shader is derived from the
background. This may be used to apply shading to the background image or
texture. Shadow and reflection catcher surfaces can be created with this
method. It does not work in QuickRender. use_background_color overrides
the shader color or color map value.
Example:
use_background_color = 0
use_fill_color
Syntax:
use_fill_color= <scalar>
Range:
0 (OFF) to 1 (ON). If a number smaller than 0 is used, use_fill_color is forced
to 0; for numbers greater than 1, use_fill_color is forced to 1.
Default:
0
362 | Chapter 6 Data types
Purpose:
Use_fill_color is only relevant to hidden-line rendering. When turned off,
only the outline of the objects are drawn in hidden-line rendering. When
turned on, the interior of the surface is filled in with the color as specified by
fill_color.
It must also be noted that when use_fill_color is turned off, the mask generated
only shows the existence of the outline. When turned on, then the entire
object’s mask value are assumed to be opaque.
Example:
use_fill_color = 0
v_patch_lines
Syntax:
v_patch_lines= <scalar>
Range:
Any value greater than 0.
Default:
0
Purpose:
V_patch_lines is only relevant in hidden-line rendering. By default, only the
outline of the surface is drawn in hidden-line rendering (i.e. when
v_patch_lines = 0). However, it is possible to get a gridded look of the outline,
in which a number of lines per isoparm can be drawn through the v-direction
of the surface. This number is the setting for v_patch_lines.
Because the gridded lines are drawn according to the uv-parameterization of
the surface, it can warp undesirably. If such a case occurs, the best solution
would be turn chord_length on in the texture definition.
Example:
v_patch_lines = 0
Shader Data Type | 363
Texture Data Type
Declaration:
texture <name> ( procedure=<procedure name>, <component list> ) ;
Reference:
<name>
Purpose:
This defines a texture. All textures are procedures, and, hence, the procedure
name is required. Each procedure has its own set of components. However,
all procedures have the following set of components in common:
■
active on page 365
■
amult on page 366
■
aoffset on page 366
■
aout on page 367
■
blurmult on page 368
■
bluroffset on page 368
■
chord_length on page 369
■
filter on page 369
■
mirror on page 370
■
offset on page 371
■
repeat on page 371
■
rotate on page 372
■
rgbmult on page 372
■
rgboffset on page 373
■
rgbout on page 374
■
scale on page 374
■
translate on page 375
364 | Chapter 6 Data types
■
wrap on page 376
■
worldspace on page 376
Comments:
All components are specified using a keyword=value form.Components are
separated by commas. Not all components are optional. The components may
be specified in any order. Components which are not specified take on their
default value. If any component is specified more than once, the last such
specification will be used, and all previous ones ignored. Not all components
are meaningful in all combinations. In situations where a component is not
meaningful, any specification of it will be ignored with no ill effect.
Only those components common to all texture procedures are described here,
See the description of the individual texture procedures for definition of the
components unique to each. Note that texture components are not reserved
words (and, thus, are not printed in bold here), although the terms texture
and procedure both are reserved.
Example:
texture marb ( procedure = SmarbleRGB,
wrap = FALSE,
blurmult = 0.5
);
active
Syntax:
active
Range:
0 (FALSE) or not 0 (TRUE)
Default:
TRUE
Texture Data Type | 365
Purpose:
active sets a flag indicating whether or not a given texture is to be used in the
rendering process.
amult
Syntax:
amult = <scalar>
Range:
Generally, a useful range is from -1.0 to 1.0.
Default:
1.0
Purpose:
Value multiplier factor. All values of the texture are multiplied by this.
Comments:
This component may be animated.
NOTE The attribute being textured often has a limited range, so the value used
for amult will have de facto limits in that context. For example, transparency is
limited to the range 0 to 1. If an amult of -1 is used, then a corresponding aoffset
must also be used to prevent the entire coverage area from bottoming out to zero.
Example:
amult = -1.0
aoffset
Syntax:
aoffset = <scalar>
366 | Chapter 6 Data types
Range:
A useful range is from -1.0 to 1.0.
Default:
0.0
Purpose:
Value offset factor. This is added to each value in the texture.
Comments:
This component may be animated.
Example:
aoffset = 1.0
aout
Syntax:
aout = <scalar>
Range:
0 to 1
Default:
0
Purpose:
Value outside of the area influenced by the texture.
Comments:
This component may be animated.
Texture Data Type | 367
Example:
aout = 0.5
blurmult
Syntax:
blurmult = <scalar>
Range:
Non-negative. Generally, a useful range is from 0.0 to 10.0.
Default:
1.0
Purpose:
Scaling factor for blur of texture.
Comments:
This component may be animated.
Example:
blurmult = 0.2
bluroffset
Syntax:
bluroffset = <scalar>
Range:
Non-negative. Generally, a useful range is from 0.0 to 1.0.
Default:
0.0
368 | Chapter 6 Data types
Purpose:
Offset value for blur of texture.
Comments:
This component may be animated.
Example:
bluroffset = 0.001
chord_length
Syntax:
chord_length= <scalar>
Range:
0 (FALSE) to non-zero (TRUE)
Default:
FALSE
Purpose:
This flag maps a parametric texture so that it conforms to the curvature of the
surface, not to the isoparametric surface values.
Example:
chord_length = TRUE;
filter
Syntax:
filter= <scalar>
Texture Data Type | 369
Range:
0 (OFF), 1 (BLEND_FILTER), 2 (QUADRATIC_FILTER), 3 (QUARTIC_FILTER),
4(GAUSS_FILTER)
Default:
BLEND_FILTER
Purpose:
This flag selects a filter to use with file texture.
Example:
filter= BLEND_FILTER;
mirror
Syntax:
mirror
Range:
0 (FALSE) or not zero (TRUE)
Default:
FALSE
Purpose:
If mirror is TRUE, then repeated “tiles” of a texture are alternately flipped.
Thus the colors at the seams will match, hiding the seams.
Comments:
This can be useful when trying to cover a large surface with a small texture
sample. Note, however, that blur does not work across the seam when mirror
= TRUE, and seams will appear between tiles if the texture is blurred.
370 | Chapter 6 Data types
For high quality seamless wrapping of textures, use the standalone “Fixwrap”
on the source pix file instead of mirror. Fixwrap is included with alias_gifts.
Type “fixwrap” without arguments for help information.
offset
Syntax:
uoffset = <scalar>,
voffset = <scalar>,
Range:
-infinity to infinity
Default:
0
Purpose:
uoffset and voffset determine the positioning of a texture within the coverage
area.
Example:
uoffset = 0.989796, voffset = -0.3453,
repeat
Syntax:
urepeat = <scalar>,
vrepeat = <scalar>,
Range:
-infinity to 5
Default:
1
Texture Data Type | 371
Purpose:
urepeat and vrepeat determine how many copies of the texture there are within
the coverage area.
Example:
urepeat = -2.360882, vrepeat = 98.614067,
rotate
Syntax:
rotate = <scalar>,
Range:
-360 to 360
Default:
0
Purpose:
rotate is used to set the rotation (in degrees) of a texture on a shader.
Example:
rotate = 143.265305,
rgbmult
Syntax:
rgbmult = <triple>
Range:
Generally, a useful range for each component of the triple is from 0.0 to 1.0.
Default:
(1.0, 1.0, 1.0)
372 | Chapter 6 Data types
Purpose:
Provides a scaling factor for the value.
Comments:
This component may be animated.
The red, green, and blue components of the texture are multiplied by the
numbers specified in the rgbmult triplet. The default of (1.0, 1.0, 1.0) means
that all values are multiplied by 1, and are not changed. To darken the red
component of a texture, reduce the first number. Using (0.5, 1.0, 1.0) results
in the range for the red component being reduced to 0-128, and leaves the
green and blue components at their full values. To increase the range of a
component, use a number greater than 1. Be aware that you can’t get any
brighter than 255 for each component.
Example:
rgbmult = ( sqrt(2), 1.0, 0.0 )
rgboffset
Syntax:
rgboffset = <triple>
Range:
A generally useful range for each component of the triple is from 0.0 to 255.0.
Default:
( 0.0, 0.0, 0.0 )
Purpose:
Offset for value. This is added to each value in the texture.
Comments:
This component may be animated.
Texture Data Type | 373
Example:
rgboffset = ( 0.0, -128.0, 0.0 )
rgbout
Syntax:
rgbout = <triple>
Range:
Generally, a useful range for each component of the triple is 0.0 to 255.0.
Default:
( 0.0, 0.0, 0.0 )
Purpose:
Defines the value outside of the area influenced by the texture.
Comments:
This component may be animated.
Example:
rgbout = ( 255.0, 255.0, 255.0 )
scale
Syntax:
uscale = <scalar>
vscale = <scalar>
sx= <scalar>
sy= <scalar>
Range:
Non-negative.
374 | Chapter 6 Data types
Default:
1
Purpose:
The value assigned to uscale and vscale indicates the relative size of the texture
map on the object 1 gives a full copy of the texture map. A scale of 0.5 means
that the size of the texture map is double that of a scale of one: that is, only
half of the texture map fits on the object. Scale is assigned in both u and v
directions.
Sx and sy are only relevant to the Camera Type in Solid Projection. They store
the scaling factors from the filmback space to image plane space.
translate
Syntax:
utranslate= <scalar>,
vtranslate = <scalar>,
tx= <scalar>,
ty= <scalar>,
Range:
-infinity to infinity
Default:
0
Purpose:
utranslate and vtranslate determine the placement of the area of coverage on
a texture.
tx and ty are only relevant to the Camera Type in Solid Projection. They store
the translation factors from the filmback space to image plane space.
Example:
utranslate = -3.511901, vtranslate = 1.0,
Texture Data Type | 375
wrap
Syntax:
uwrap = <scalar>
vwrap = <scalar>
Range:
0 or 1
Default:
1 (ON = FALSE)
Purpose:
The value assigned to wrap indicates whether the texture will replicate itself
over the entire surface in the either the u or v direction, or have only one
copy of the texture mapped. To have a single copy in one direction on the
surface, use 0 (off).
Comments:
This component may be animated.
Example:
wrap = FALSE
worldspace
Syntax:
worldspace = <scalar>,
Range:
0 or 1
Default:
1 (ON = TRUE)
376 | Chapter 6 Data types
Purpose:
worldspace sets a flag indicating whether a texture is to be rendered on a
surface using worldspace texture mapping techniques.
Transformation Data Type
Declaration:
transformation <name>;
Reference:
<name>
Purpose:
The current transformation matrix is, in fact, a set of matrices that are
maintained to relate the sense of position, orientation and size between objects
and the world coordinate system. While the internal form of these (and their
interdependencies) are not available to the user, it is convenient to be able to
store, assign and use them. The transformation data type defines variables to
do that.
There are no components of a transformation available to the user. A
transformation may not be used as a literal.
Example:
transformation sticky;
Trim boundary Data Type
Declaration:
ttb ( btype = <scalar>, <trim_edge_list> );
Literal:
tb( btype = <scalar>, te(....) ... )
Transformation Data Type | 377
Purpose:
This defines a trim boundary. A trim boundary may be specified as a literal.
A trim boundary has two arguments:
btype
specifies the trim boundary type; 1
is an inner boundary, 0 is an outer
boundary and < 0 is a segment.
<trim_edge_list>
list of one or more trim edges that define
the boundary.
Limitations:
The elements of a trim boundary must be literals. They may not be represented
by expressions or variables.
Example:
tb( btype = 0,
te(dim = 2, nbs = 6, form = 1,
tbs(ctype = 0,dim = 2,m = 3,
n = 1,rat = 1,form = 0,
tcv(0.9501376,-2.6293772,1.0,0.0),
tcv(0.9514360,-2.6064462,1.0,0.08 ),
tcv(0.9519445,-2.5832916,1.0,0.08),
tcv(0.9519445,-2.5600670,1.0,0.08)
)
)
)
Trim b-spline Data Type
Declaration:
ttbs ( ctype = <scalar>, dim= <scalar>, m= <scalar>, n = <scalar>, rat = <scalar>,
form = <scalar>, <trim_control_vertex_list> )
Literal:
te( ctype = <scalar>, dim= <scalar>, m= <scalar>, n = <scalar>, rat = <scalar>,
form = <scalar>, <trim_control_vertex_list> )
378 | Chapter 6 Data types
Purpose:
This defines a trim b-spline. A trim b-spline may be specified as a literal. A
trim b-spline has seven arguments.
ctype
the type of b-spline; general (0), line (1),
parabola(2), circle(3), ellipse (4), hyperbola
(5), or C2 cubic (10).
dim
the dimension of the trim b-spline.
m
the degree of the spline.
n
specifies the number of spans.
rat
specifies if the curve is rational (1), nonrational (0) or homogeneous (-1)
form
describes the type of edge; 0 is open, 1 is
closed, 2 is periodic, and -1 is disjoint.
The last argument is the list of two or more trim curve vertices that define the
trim b-spline
Limitations:
The elements of a trim edge (see Trim edge Data Type on page 381) must be
literals. They may not be represented by expressions or variables.
Example:
tbs(ctype = 0,dim = 2,m = 3,
n = 1,rat = 1,form = 0,
tcv(0.9501376,-2.6293772,1.0,0.0),
tcv(0.9514360,-2.6064462,1.0,0.08 ),
tcv(0.9519445,-2.5832916,1.0,0.08),
tcv(0.9519445,-2.5600670,1.0,0.08)
)
Trim b-spline Data Type | 379
Trim curve vertex Data Type
Declaration:
ttcv ( <scalar>, <scalar>, <scalar>, <scalar> )
Literal:
tcv (<scalar>, <scalar>, <scalar>, <scalar> )
Purpose:
This defines a trim curve vertex. A trim curve vertex may be specified as a
literal. All of its components are identified by position rather than by keywords.
They are interpreted as
( u, v, w, t)
where:
u and v
the parametric space coordinates of the
trim curve vertex.
w
the weight of the vertex.
t
parametric distance in the space of the
curve it helps describe.
Limitations:
The elements of a trim curve vertex must be literals. They may not be
represented by expressions or variables.
Example:
tcv (0.007, 0.65, 1.0, 0.34 ), ...
380 | Chapter 6 Data types
Trim edge Data Type
Declaration:
tte ( dim= <scalar>, nbs = <scalar>, form = <scalar>, <trim_b-spline_list> )
Literal:
te( dim= <scalar>, nbs = <scalar>, form = <scalar>, <trim_b-spline_list> )
Purpose:
This defines a trim edge. A trim edge may be specified as a literal. A trim edge
has four arguments.
dim
specifies the dimension of the trim edge.
nbs
specifies the number of b-splines that describe the trim edge.
form
describes the type of edge; 0 is open, 1 is
closed, 2 is periodic, and -1 is disjoint.
<trim_b-spline_list>
list of one or more trim b-splines that
define the trim edge.
Limitations:
The elements of a trim edge must be literals. They may not be represented by
expressions or variables.
Trim edge Data Type | 381
Example:
te(dim = 2, nbs = 6, form = 1,
tbs(ctype = 0,dim = 2,m = 3,
n = 1,rat = 1,form = 0,
tcv(0.9501376,-2.6293772,1.0,0.0),
tcv(0.9514360,-2.6064462,1.0,0.08 ),
tcv(0.9519445,-2.5832916,1.0,0.08),
tcv(0.9519445,-2.5600670,1.0,0.08)
)
)
Trim face Data Type
Declaration:
ttf name ( divs = <scalar>, <trim_boundary_list> );
Reference:
name
Literal:
tf ( divs = <scalar>, tb(....) ... )
Purpose:
This defines a trim face. A trim face may be specified as a variable or a literal.
A trim face has two arguments:
divs
specifies the number of subdivisions per
span when converting the 2D spline to a
piece-wise linear approximation.
<trim_boundary_list>
a list of trim boundaries that define regions
of the NURBS surface to keep or discard,
depending on their order. The first trim
boundary defines the boundary of a kept
region, and subsequent boundaries in the
trim face define holes. The second argu-
382 | Chapter 6 Data types
ment is a list of one or more trim boundary
curves.
Limitations:
The elements of a trim face must be literals. They may not be represented by
expressions or variables.
Example:
tf trim309948216( divs = 16,
tb( btype = 0,
te(dim = 2, nbs = 6, form = 1,
tbs(ctype = 0,dim = 2,m = 3,
n = 1,rat = 1,form = 0,
tcv(0.9501376,-2.6293772,1.0,0.0),
tcv(0.9514360,-2.6064462,1.0,0.08 ),
tcv(0.9519445,-2.5832916,1.0,0.08),
tcv(0.9519445,-2.5600670,1.0,0.08)
)
)
)
);
Trim_vertex Data Type
Declaration:
trim_vertex <name> ( <scalar>, <scalar>, <scalar> ) ;
Reference:
<name>
Literal:
trim_vertex (<scalar>, <scalar>, <scalar> )
Trim_vertex Data Type | 383
Purpose:
This defines a trim_vertex. A trim_vertex may be specified as a literal or as a
variable. If specified as a variable, it must have a name. All of its components
are identified by position rather than by keywords. They are interpreted as
( u, v, flag )
The meaning of u and v are the parametric space coordinates of the
trim_vertex. The flag is interpreted as a Boolean. Zero (FALSE) means that this
trim_vertex is interior to the surface it is associated with and trim curve
algorithms should be used for processing it. Any other value (TRUE) means
that this trim_vertex lies on the boundary of the surface and NURB curve
algorithms should be used for processing it.
Limitations:
The elements of a trim_vertex must be literals. They may not be represented
by expressions or variables.
Example:
trim_vertex nave (0.007, 0.65, 0 );
Triple Data Type
Declaration:
triple <name> ( <scalar>, <scalar>,<scalar> );
Reference:
<name>
Literal:
( <scalar>, <scalar>, <scalar> )
Purpose:
A triple may be specified as a literal or as a variable. If specified as a variable,
it must have a name. The components of a triple are just the 3 values, which
are identified by position rather than by keywords.
384 | Chapter 6 Data types
Example:
triple origin( 0, 0, 0 );
Triple Data Type | 385
386
Scene Description
Language Reference
7
Using Data Items
Once a variable has been declared, it may be referenced. The reference to a
variable may occur in the sense of retrieval, where the variable may be thought
of as a source of values to be used. When referenced in this way, a variable
behaves as though a corresponding literal had been used in place of the reference.
This usage of variables is permitted anywhere in SDL, providing the variable
being referenced has already been declared. Thus, it is possible to declare a
<scalar>:
scalar max_color(255);
Then immediately use it to declare another variable, e.g.
triple white( max_color, max_color, max_color );
Indeed, this is exactly how normal use of SDL will proceed, with the declaration
of basic building blocks followed by even larger pieces until all the items needed
for the model have been defined. Thus, variables of the elementary data types
(i.e., scalar, triple, CV, filename, shader, texture, array) will commonly be
refer-enced as part of the declaration of other variables, or in the specification
of liter-als. References to vari-ables of the data types for “primitive objects” (i.e.,
light, patch, face) will normally be in the MODEL section of SDL where they
will be used to create an instance of the object represented by the variable. Some
of the data types provided in SDL are complex compositions of many
com-ponents.
Some operations are defined for all data types, while other operations depend
upon the data type. There are common operations which are allowed for
387
vari-ables of all data types except as noted below. These common operations
are:
■
a variable may be printed,
■
a variable may be assigned the value of another variable of the same type,
■
a variable may be assigned the value of an array element of the same type,
■
a variable may be assigned the value of a literal of the same type,
■
a variable may have its values assigned to another variable of the same
type,
■
a variable may have its values assigned to an array element,
■
a variable may be referenced wherever a literal of the same type may be
used.
An exception to the above is that there is no such thing as a literal (to serve
as the source of an assignment) for some data types, namely: shaders and
transforma-tions. Note that printing means that the values of the components
defining the variable will be output to “stderr”, not that some graphic rendition
will be at-tempted. Note that operations on a scalar are the same as previous
versions of SDL. This includes general usage in arithmetic expressions (see
“expressions” be-low). While there is no such thing as a literal transformation,
a variable of type transformation can have the cur-rent model transform
assigned to it.
Arrays are special. While the above operations are valid and true for arrays,
they don’t give the full picture. Therefore, the operations will be reconsidered
here for ar-rays.
■
An array may be printed. This means that each element in the array will
be printed as though it were an independent variable.
■
An array may have the contents of another array assigned to it. If the two
arrays have the same number of elements, then the assignment takes place
on an element by element basis. If the two arrays have a different number
of elements, it is considered a syntax error, and execution terminated.
■
A variable or a literal of any data type may be assigned to an array element.
No checking of the array element’s previous contents is made, so the new
value may be a different type from the previous.
■
An array element may be used in place of a variable. The type of the present
contents of the array element is considered the type of the element. That
388 | Chapter 7 Scene Description Language Reference
is, type checking of elements is performed at reference time (not
assignment).
■
Note that arrays have undefined element contents and undefined element
types (unless an initial value is specified when the array is declared) until
the element is given some value by assignment.
System Defined Variables
There are some variables which are defined as part of the SDL. These vari-ables
are always defined, and may be referenced as desired. Their values are set and
maintained automatically. In most cases (the exceptions will be noted), these
vari-ables may not be updated or changed by the user.
The majority of the variables correspond to the operational parameters. Those
that do correspond have a default value, but may be set from command line
ar-guments or by assignment in the DEFINITION section. Each variable is
described below. System Defined Constants on page 392 are described after the
variables.
The following variables are described in this topic.
■
aalevelmax on page 390
■
aalevelmin on page 390
■
aathreshold on page 390
■
byframe on page 390
■
endframe on page 390
■
frame on page 391
■
quiet on page 391
■
startframe on page 391
■
xleft on page 391
■
xright on page 392
■
yhigh on page 392
■
ylow on page 392
System Defined Variables | 389
aalevelmax
This variable corresponds to the operational parameter aalevelmax. It has a
default scalar value of 2, but may be set from the -a command line option (see
Command Line Options on page 11) or by assign-ment in the DEFINITION
Section on page 49. It sets the maximum anti-aliasing level that will be used
when rendering an image. Note that it may not be set by assignment (or by
any other means) in any section except the DEFINITION section. See the
de-scription of DEFINITION parameters for the meaning of this data and the
values that it may take.
aalevelmin
It has a default scalar value of 1, but may be set by assign-ment in the
DEFINITION Section on page 49. Note that it may not be set by assignment
(or by any other means) in any section except the DEFINITION section. See
the de-scription of DEFINITION parameters for the meaning of this data and
the values that it may take.
aathreshold
This variable corresponds to the operational parameter aathreshold. It has a
de-fault scalar value of 160, but may be set from the -t command line option
(see Command Line Options on page 11) or by as-signment in the DEFINITION
Section on page 49. Note that it may not be set by assign-ment (or by any
other means) in any section except the DEFINITION section. See the
descrip-tion of DEFINITION parameters for the meaning of this data and the
values that it may take.
byframe
This variable corresponds to the operational parameter byframe. It has a default
scalar value of 1, but may be set from the -b command line option (see
Command Line Options on page 11) or by assign-ment in the DEFINITION
Section on page 49. Note that it may not be set by assignment (or by any other
means) in any section except the DEFINITION section. See the de-scription
of DEFINITION parameters for the meaning of this data and the values that
it may take.
endframe
This variable corresponds to the operational parameter endframe. It has a
de-fault scalar value of 1, but may be set from the -e command line option
(see Command Line Options on page 11) or by as-signment in the DEFINITION
390 | Chapter 7 Scene Description Language Reference
Section on page 49. Note that it may not be set by assignment (or by any other
means) in any section except the DEFINITION section. See the description of
DEFINITION parameters for the meaning of this data and the val-ues that it
may take.
frame
This variable takes on scalar values from startframe to endframe at intervals
of byframe during the rendering process. It may be thought of as the sense of
time, or current “frame” within an animation. It need not be an integer value.
It may not be modified by the user in any way, nor will its value ever be outside
the specified range.
quiet
This variable corresponds to the operational parameter quiet. It has a default
scalar value of FALSE, but may be set from the -q command line option (see
Command Line Options on page 11) or by as-signment in the DEFINITION
Section on page 49. Note that it may not be set by assignment (or by any other
means) in any section except the DEFINITION section. See the description of
DEFINITION parameters for the meaning of this data and the val-ues that it
may take.
startframe
This variable corresponds to the operational parameter startframe. It has a
default scalar value of 1, but may be set from the -s command line option (see
Command Line Options on page 11) or by assignment in the DEFINITION
Section on page 49. Note that it may not be set by assign-ment (or by any
other means) in any section except the DEFINITION section. See the description
of DEFINITION parameters for the meaning of this data and the values that
it may take.
xleft
This variable corresponds to the operational parameter xleft. It has a default
scalar value of 0, but may be set from the -x command line option (see
Command Line Options on page 11) or by assign-ment in the DEFINITION
Section on page 49. Note that it may not be set by assignment (or by any other
means) in any section except the DEFINITION section. See the de-scription
of DEFINITION parameters for the meaning of this data and the values that
it may take.
System Defined Variables | 391
xright
This variable corresponds to the operational parameter xright. It has a default
scalar value of 644, but may be set from the -w command line option (see
Command Line Options on page 11) or by as-sign-ment in the DEFINITION
Section on page 49. Note that it may not be set by assignment (or by any other
means) in any section except the DEFINITION section. See the description of
DEFINITION parameters for the meaning of this data and the val-ues that it
may take.
yhigh
This variable corresponds to the operational parameter yhigh. It has a default
scalar value of 485, but may be set from the -h command line option (see
Command Line Options on page 11) or by as-signment in the DEFINITION
Section on page 49. Note that it may not be set by assignment (or by any other
means) in any section except the DEFINITION section. See the description of
DEFINITION parameters for the meaning of this data and the val-ues that it
may take.
ylow
This variable corresponds to the operational parameter ylow. It has a default
scalar value of 0, but may be set from the -y command line option (see
Command Line Options on page 11) or by assign-ment in the DEFINITION
Section on page 49. Note that it may not be set by assignment (or by any other
means) in any section except the DEFINITION section. See the description of
DEFINITION parameters for the meaning of this data and the values that it
may take.
System Defined Constants
Like the system defined variables, there are some constants which are defined
as part of the SDL. These constants are always defined, and may be refer-enced
as desired. Each is described below.
The following constants are defined in this section.
■
FALSE on page 393
■
OFF on page 393
■
ON on page 393
392 | Chapter 7 Scene Description Language Reference
■
TRUE on page 393
■
xaxis on page 393
■
yaxis on page 393
■
zaxis on page 394
FALSE
This is a constant with the scalar value of 0. It is useful when a constant truth
value is desired. Note that the value is identical to the constant OFF, with
which it is inter-changeable.
OFF
This is a constant with the scalar value of 0. It is useful when a constant truth
value is desired. Note that the value is identical to the constant FALSE, with
which it is inter-changeable.
ON
This is a constant with the scalar value of 1. It is useful when a constant truth
value is desired.
Note that the value is identical to the constant TRUE, with which it is
inter-changeable.
TRUE
This is a constant with the scalar value of 1. It is useful when a constant truth
value is desired. Note that the value is identical to the constant ON, with
which it is inter-changeable.
xaxis
This is a constant with the scalar value of 0. It is meant to describe one of the
possible axes of rotation for use in the rotate on page 43statement. See the
description of that statement for more information on the meaning of the
possible axes.
yaxis
This is a constant with the scalar value of 1. It is meant to describe one of the
possible axes of rotation for use in the rotate on page 43 statement. See the
System Defined Constants | 393
description of that statement for more information on the meaning of the
possible axes.
zaxis
This is a constant with the scalar value of 2. It is meant to describe one of the
possible axes of rotation for use in the rotate on page 43 statement. See the
description of that statement for more information on the meaning of the
possible axes.
Expressions
There are three types of expressions: Primary Expressions on page 394, Unary
Operator Expressions on page 395 and Binary Operator Expressions on page
396. These will be described in turn.
Functions on page 397 are described in the next section.
Primary Expressions
Primary expressions may be further divided into five kinds:
1) Variables,
2) Array Elements,
3) Literals,
4) Function Calls, and
5) Parenthesized Expressions.
Array Elements
An array element may be used as an expression if 1) the subscript referencing
it is in the range defined when the array was declared, and 2) the type of the
element is scalar. Since the subscript itself may be a variable and the contents
of an array ele-ment may be of any type, the test for the above conditions is
made at reference time.
Function Calls
Only functions which return a scalar may be used as an expression. The syntax
of a function call is:
394 | Chapter 7 Scene Description Language Reference
<function name> ( <argument list> )
The contents of the argument list vary depending upon the function being
in-voked. The reader is referred to the detailed descriptions of the individual
func-tions for the specification of the arguments required by each. Note that
the argu-ment list may be empty for some functions, but the delimiting
parentheses are still required. As with “C”, function arguments are passed by
value, and the ar-guments themselves will not be affected in any way by the
function call.
Literals
Only literals of type scalar may be used as an expression. The value given is
used.
Parenthesized Expressions
A parenthesized expression consists of a left parenthesis, any expression, and
then a right parenthesis — ( <expression> )
The purpose of the parenthesized expression is simply to delimit the enclosed
ex-pression for grouping purposes. Normally the enclosed expression will be
a binary operator expression, although any type of expression is valid. The
classic example is a grouping to defeat the normal precedence of operators
with a binary operator ex-pression — ( x + 1 ) / 2
Variables
Only variables of type scalar may be used as an expression. Since variables of
that type always have a value defined, the use of a variable as an expression
is just a ref-erence to that value.
Unary Operator Expressions
Two unary operators are provided, logical negation ( ! ), and arithmetic
negation ( – ). In both cases the syntax is:
<operator><primary expression>
where <operator> is either “!” or “-”. Any primary expression is valid, but only
a primary expression. Logical negation results in a value for the expression of
ei-ther 0 (FALSE) or 1 (TRUE). A value of 1 results when the <primary
expression> has a value of zero. A value of 0 results when the <primary
expression> has any other (non-zero) value. Arithmetic negation simply
changes the sign of the value of the <primary expression>. Zero is unsigned
Expressions | 395
and unaffected by this operator. Logical negation takes precedence over
arithmetic negation.
Binary Operator Expressions
A binary operator expression consists of 2 expressions (of any kind) separated
by a binary operator. There are 12 binary operators, which have 5 different
levels of precedence, namely:
* / highest precedence
+== != >= <= > <
&&
|| lowest precedence
All binary operators have a lower precedence than the unary operators. All
bi-nary operators are left associative. The individual operators will be discussed
in order of decreasing precedence.
Multiplication ( * ) and division ( / ) have the same precedence. All arithmetic
is per-formed in single precision floating point form. Division by zero is invalid
and results in a terminated execution. Addition ( + ) and subtraction ( – ) have
the same prece-dence, which is lower than multiplication or division. The
computa-tion is performed in single precision floating point form.
The operators “<”, “>”, “<=”, “>=”, “==” and “!=” are collectively known as
trela-tion operators. They represent “less than”, “greater than”, “less than or
equal to”, “greater than or equal to”, “equality”, and “not equal”, respectively.
All the relation operators have the same precedence. The relation operators
compare the values of 2 expressions. The result of such a comparison is either
1 in the case where the speci-fied relationship exists (the TRUE case) or 0 in
the case where the relation does not exist (FALSE).
All comparisons are between single precision floating point numbers. The user
is therefore advised to exercise care when using tests for equality. A second
poten-tial problem could occur because of the left associativity combined with
all rela-tion op-erators having the same precedence and the left to right
evaluation order of expres-sions. The user is urged to use explicit grouping
whenever more than one relation operator is needed.
Consider, for example,
a>b>3
This will always evaluate to 0 (FALSE), because the associativity results in
396 | Chapter 7 Scene Description Language Reference
(a>b)>3
and the result of a > b must be either 1 or 0, neither of which is greater than
3.
The logical AND operator ( && ) interprets the two expressions as truth values
and performs the logical intersection. An expression is considered true if its
value is non-zero, and false if its value is zero. The result of the intersection
is either 1 (in the case where the expressions are both true) or 0 (for all other
cases). Note that the left ex-pression is evaluated first, and if it is false then
the result is deter-mined and the right expression is not inspected at all. This
behavior is similar to the “C” language and is sometimes useful when the
value of an expression might not be well defined (as with arrays for instance).
The logical OR operator ( || ) interprets the two expressions as truth values
and performs the logical union. An expression is considered true if its value
is non-zero, and false if its value is zero. The result of the union is either 1 (in
the case where ei-ther of the expressions are true) or 0 (in the case where both
expressions are false). Note that the left expression is evaluated first, and if it
is true then the result is de-termined and the right expression is not inspected
at all. This behavior is similar to the “C” language and is sometimes useful
when the value of an ex-pression might not be well defined (as with arrays
for instance).
Functions
There are a number of functions defined for SDL that may be used in an
expres-sion or in place of an expression. Most functions (there are a few
exceptions) return a single (scalar) value. Most functions are simply routines
from the standard UNIX math library. These will not be documented, defined,
or described here. The reader is referred to the standard UNIX documentation.
They are:
besselj0 besselj1 besseljn
besselyn
cos acos cosh
erf erfc
exp
fabs
floor ceil
Functions | 397
hypot
log10
pow
sin asin sinh
sqrt
tan atan atan2 tanh
Some basic extensions to the trigonometric functions are provided so that
angles may be expressed in degrees rather than radians:
cosd acosd
sind asind
tand atand atan2d
These are identical to the standard routines in all respects except that the
angles are expressed in degrees.
In addition to the math library routines, SDL has the following functions
defined:
animate on page 399
cl() [formerly cluster()] on page 399
constrain( ) on page 400
current_position on page 400
current_transformation on page 400
ease on page 401
extract on page 402
fmod on page 402
gamma on page 403
motion on page 403
rand on page 404 srand on page 404 gauss on page 403
sign on page 404
Each of these is described in detail below.
398 | Chapter 7 Scene Description Language Reference
animate
The animate function is used to define animated behaviors. It takes 2
arguments, and returns a scalar:
animate( <parameter_curve>, <time> )
The <parameter_curve> argument defines the parameter curve to be used for
an animation. It must be the name of a <parameter_curve> variable defined
in the definition section. The <time> argument specifies where along the curve
to interpret the value. It is a scalar, and will nor-mally be the system defined
variable frame. The animate function returns a scalar. The value re-turned is
the value of the <parameter_curve> at time <time>.
Example:
translate(animate( sphere.X_Position, frame ), 0.0, 0.0);
cl() [formerly cluster()]
Returns:
CV
Syntax:
cl( <cv>, <cluster_matrix_reference>, <percentage> [,
<cluster_matrix_reference>, <percentage> ] )
The cl or cluster function takes <cv> and applies the specified clusters at the
given percentages.
For a description of how clusters are applied to CVs, please check the animation
section of the documentation.
Example:
cl(cv((-0.928135, -0.066296, 3.525111), 1.0),
CL_cluster#2 ,0.0,
CL_knot100_section270_Relbow ,0.003524,
CL_knot0_section270_Relbow ,0.879251,
CL_knot26_section0_Relbow ,0.007034,
CL_knot0_section0_Relbow ,0.462762) )
Functions | 399
constrain( )
Syntax:
constrain ( start, end, by, constrain_value )
Constrain function takes 4 scalar arguments. The return value is constrained
to be start, end, or (start + N * by) where (N * by) is not greater than (end start). The start value must be less than the end value. If (constrain_value <=
start) then start is returned. If (constrian_value >= end) then end is returned.
If (by = 0), then the function will always return the start value. This function
is useful for animating visibility exactly, or turning a smooth curve into discrete
steps.
Example:
The following function will return 19, because its possible return values are
13, 16, 19, 22, and 25.
x = constrain ( 13, 25, 3, 18 );
current_position
This function returns a triple value corresponding to the x, y, and z coordinates
of a point in space defined in the model where the function is called. It takes
a triple as an argument. Its value outside the MODEL section is undefined,
and any references to it outside that section are invalid and will generate an
error.
Example:
<triple_variable> = current_position( x, y, z );
or
<triple_variable> = current_position( motion(
<motion_path>, animate( <timing_curve>, frame )));
current_transformation
This function returns a transformation value corresponding to its placement
in the modeling hierarchy. It does not take any arguments. It is used primarily
to mark the location of a solid texture or a cluster. Its value outside the MODEL
section is undefined, and any references to it outside that section are invalid
and will generate an error.
400 | Chapter 7 Scene Description Language Reference
Example:
<texture_orientation> = current_transformation();
ease
The ease function takes 5 arguments. It returns a scalar. It is used primarily
for ani-mation.
Syntax:
ease ( <start_val>, <end_val>, <keyword>, <startframe>, <endframe> )
<start_val> is the value returned when the value of frame is less than or equal
to <startframe>.
<end_val> is the value returned when the value of frame is greater than or
equal to <endframe>.
<keyword> determines how the value to be returned is determined when the
value of frame is between <startframe> and <endframe>. It can be any of:
EXPOUT, OUT, INOUT, LINEAR, IN, or EXPIN. (Note the use of full capitals.)
The following chart provides the functions f(x) which define the shape of the
ease curves:
keyword:
f(x) range of x
IN:
cos (x) 0 <= x <= 90
OUT:
cos (x) -90 <= x <= 0
INOUT:
-cos (x) 180 <= x <= 360
EXPOUT:
((<frame> - <start frame>)/(<end frame>
- <start frame>))0.3
EXPIN:
((<frame> - <start frame>)/(<end frame>
- <start frame>))1.8547
LINEAR:
x unbounded
The keyword determines the rates of acceleration and deceleration of the
charac-teris-tic under animation. The computer interpolates the value being
Functions | 401
animated and makes this change across the necessary number of frames, easing
in or out according to the type of curve selected.
<startframe>
is an scalar that indicates the starting frame of the ease.
<endframe>
is an scalar that indicates the ending frame of the ease.
Example:
light(intensity=ease(1.0,0.0,LINEAR,startframe,endframe), col
or=(255,0,0));
extract
Allows individual channels of a triple to be extracted as scalars. Most useful
for getting at the individual values of a motion path. Extract has two
arguments, a scalar, which specifies the element to extract and a triple from
which the element will be extracted. The first scalar argument must be one
of (1, 2, 3) meaning return the first, second, or third scalar of the following
triple.
This function returns a scalar.
Example
x = extract(1.0, motion(motion_path, animate(param_curve.Timing,
frame)));
fmod
The fmod function takes 2 arguments. It returns a scalar, whose value is the
floating point remainder of the division of the first argument by the second
ar-gument. If the divisor is zero, then an error is reported and execution
terminated. The result will have the same sign as the dividend. Note that this
is a custom built Animator function because not all UNIX systems provide it.
Example:
even = fmod(frame,2);
402 | Chapter 7 Scene Description Language Reference
gamma
Given floating point output color (R, G, B), the user-supplied gamma_value,
and the function “pow(X,Y)” which raises X to the power of Y, gamma in the
renderer is applied:
R=255.0*pow((R/255.0), gamma_value);
G=255.0*pow((G/255.0), gamma_value);
B=255.0*pow((B/255.0), gamma_value);
/*Clip the value to 255.*/
if (R>255.0) R=255.0;
if (G>255.0) G=255.0;
if (B>255.0) B=255.0;
gauss
The gauss function does not take any arguments. (The syntax still requires
that parentheses be included, however.) It returns a scalar whose value is a
pseudo ran-dom number with a gaussian (normal) distribution. The random
number function may be initialized by using the srand function to set the
seed. If srand is not called, the default seed value will be used. See the
description of srand for de-tails. Note that even though the routines to compute
random numbers are the same, the numbers returned may be different on
different machines because of differences in the under-lying hardware.
Example:
distrib = gauss();
motion
The motion function is used to define animated behaviors. It takes 2
arguments:
motion( <curve>, <distance> )
The <curve> argument defines a 3D curve to be used for an animation. It will
be the name of a curve variable. The <distance> argument specifies where
along the curve to interpret the value. It is a scalar, and specifies the parametric
dis-tance along the curve. The parametric distance is 0 at the end of the curve
corre-sponding to the first CV and 1 at the end of the curve corresponding to
Functions | 403
the last CV. Normal usage of the motion function will relate the parametric
distance to frame time by way of a nested animate. For example,
motion( some_path, animate( timing_curve, frame ))
The motion function returns a triple. The value returned is the point along
the <curve> at <distance> from the end. If <distance> is outside the range 0
to 1, then the value of <curve> at one end or the other (the start if <distance>
is less than 0, the end if <distance> is greater than 1) will be given.
rand
The rand function does not take any arguments. (The syntax still requires that
parentheses be included, however.) It returns a scalar whose value is a pseudo
ran-dom number uniformly distributed between -1.0 and 1.0. The random
number func-tion may be initialized by using the srand function to set the
seed. If srand is not called, the default seed value will be used. See the
description of srand for de-tails. Note that even though the routines to compute
random numbers are the same, the numbers returned may be different on
different machines because of differences in the underlying hardware.
Example:
flake = rand();
sign
The sign function takes one argument. It returns a scalar with the value -1 if
the ar-gument is negative, 0 if the argument is 0, or +1 if the argument is
positive.
Example:
if (sign(byframe)) print("infinite loop");
srand
The srand function takes one argument. It returns a scalar with the constant
value 0. The argument provided will be used as the initial seed for random
num-ber genera-tion. The argument should be a scalar. If the argument is
omitted or of the wrong type, a warning message will be generated, the default
seed value will be used, and execution will continue as if everything were
correct. The default seed value is
12345.
404 | Chapter 7 Scene Description Language Reference
Example:
bogus = srand(54321);
warp
The warp function is used to globally change the timing of animation
parameters. It takes 2 arguments:
warp( <curve>, <time> )
The <curve> argument defines the parameter curve to be used for an animation.
It will normally be a <parameter_curve> <parameter_vertex>s. The <time>
argument specifies where along the curve to interpret the value. It is a scalar,
and will nor-mally be the system defined variable frame. The warp function
returns a scalar. The value re-turned is the value of the <curve> at time <time>.
If <time> is below the first specified value of the <curve>, the value returned
is:
start_value - (start_value - <time>)
If <time> is greater than the last value, then the value returned is:
end_value + (<time> - end_value)
In other words, above (or below) the valid range for a warp function, the
function increases (or decreases) linearly from the end (or start) values.
Example:
animate (“transZ.curve”, warp(“rotateX.curve”, warp(transY.curve”,
frame)));
Please note that this function is obsolete.
Functions | 405
406
Procedural Textures and
Natural Phenomena
8
The following procedures are part of the standard AliasStudio package:
Atmospheric Effects:
Fog on page 412
Parametric procedural textures:
Bulge on page 415
Checker on page
417
Cloth texture on
page 419
File texture on page
422
Fractal on page 427
texture
Grid on page 425
texture
Mountain on page
430
Noise on page 433
Ramp on page 435
Stencil on page 439
Water on page 444
Projection on page
450
sCloud on page 459
sFractal on page 462
sRock on page 463
sMarble on page
465
Snow on page 465
Leather on page 456
Granite on page 452
Volume on page 469
sWood on page 467
Solid procedural
textures:
407
Environment textures:
Ball on page 473
Chrome on page
475
Cube on page 479
Sky on page 481
Sphere on page 477
Common Texture Parameters
The following texture parameters are common to all texture procedures. They
control the texture blur and intensity.
Parameter
Absolute
Range
Useful Range
Default
Description
blurmult
-infinity, infinity
0.0, 1.0
1.0
multiplier
factor used to
blur a texture
bluroffset
-infinity, infinity
0.0, 1.0
0.0
additive factor
used to blur a
texture
aout
-infinity, infinity
-1.0, 1.0
0.0
value of “a”
outside textured area
amult
-infinity, infinity
-1.0, 1.0
1.0
mult value for
intensities of
single-channel
textures.
aoffset
-infinity, infinity
-1.0, 1.0
0.0
offset value for
intensities of
single-channel
textures
408 | Chapter 8 Procedural Textures and Natural Phenomena
rgbout (triple)
0.0, 255.0
0.0, 255.0
0.0
color of shader
outside textured area
rgbmult
(triple)
-infinity, infinity
-1.0, 1.0
1.0
multiplicative
factor for colors, to scale
them up or
down.
rgboffset
(triple)
-infinity, infinity
-1.0, 1.0
0.0
offset factor for
colors, to
boost the RGB
values by an
additive
amount.
Note that the choice of whether “a” values or “RGB” values are used depends
on the feature being textured.
For example, if transparency is being textured, then the “a” parameters are
relevant, because transparency is a single channel feature. However, if
incandescence were being textured, then the “RGB” parameters would apply,
as incandescence is a three channel feature.
Common Parametric (2D) Texture Parameters
The following texture parameters are common to parametric (2D) textures:
Parameter
Absolute
Range
Useful Range
Default
Description:
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
within coverage area.
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
Common Parametric (2D) Texture Parameters | 409
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
410 | Chapter 8 Procedural Textures and Natural Phenomena
worldspace
TRUE FALSE
rotate
-infinity, infinity
mirror
TRUE FALSE
-360.0, 360.0
FALSE
flag to use
world space
texture mapping
0.0
angle coverage
area to be rotated
FALSE
flag to match
edges of texture
The parametric textures are: Bulge on page 415, Checker on page 417Cloth
texture on page 419, File texture on page 422, Fractal on page 427, Grid on page
425, Mountain on page 430, Noise on page 433, Ramp on page 435, Stencil on
page 439, and Water on page 444.
Solid and Environmental Texture Parameters
The following texture parameters are common to Solid Textures and
Environments:
■
transformation_name
The following texture parameters are common to Solid Textures, with the
exception of sRock, Snow and Leather.
Parameter
Absolute
Range
Useful Range
Default
Description
xripples
0, infinity
0, 100
1.0
Fundamental
frequencies for
noise function
yripples
0, infinity
0, 100
1.0
""
zripples
0, infinity
0, 100
1.0
""
Solid and Environmental Texture Parameters | 411
level_min
0, infinity
0, 50
0.0
Minimum allowed level of
iteration
level_max
0, infinity
0, 50
20.0
Maximum allowed level of
iteration
ratio
0, 1
0, 1
0.707
Ratio for fractal
noise
Please note that X,Y, and Z refer to the height, width, and depth respectively
of the scene as it would appear in the FRONT window, regardless of coordinate
system.
The solid textures are: Projection on page 450sCloud on page 459, sFractal on
page 462, sRock on page 463, sMarble on page 465, Snow on page 465, Leather on
page 456, Granite on page 452, Volume on page 469, and sWood on page 467.
The environment textures are: Ball on page 473Chrome on page 475, Cube on
page 479, Sky on page 481, and Sphere on page 477.
Textures
Fog
Atmospheric effects like fog describe what happens to a ray when it travels
between surfaces. In a perfect vacuum, a ray travels without being reduced,
and no light is scattered along the path of the ray from the light sources. This
is typically the case in most computer graphics images. A clear, hard-edged
look results. However, in real life, dust or smoke particles float in the air; they
obscure distant objects and scatter light to produce a mist color.
The appearance of the atmospheric effects depends on several factors.
One factor is the distribution of particles in the atmosphere. A column of
smoke has an evident concentration of particles in particular locations. Distinct
puffs are visible. This type of atmospheric effect can be emulated by using the
sCloud procedural texture. See the section on sCloud in this chapter for further
information on using this procedure.
412 | Chapter 8 Procedural Textures and Natural Phenomena
AliasStudio has three different types of fog:
Constant density fog
equal densities of particles at all locations:
distant objects fade equally in all directions.
View in any direction blends to a constant
color if there are no obstructing surfaces.
Max/Min fog
This is the same as Constant density fog
except that the max and min distances are
used to ‘clip’ the fog. That is, the fog
particles only exist between the max and
min distances from the camera.
Layered fog
fog density varies with altitude.
In the fog procedure, the color for infinite distances is defined by selecting a
Fog color. The relative scattering of light is controlled using the Fog Depth
slider. Optical depth, roughly speaking, is the distance away that a surface
must before it has half its light is scattered by the intervening air. For an
outdoor scene during the day, the fog color should be white. For smog, try
using a high layered fog and a brownish color.
To create a scene with the impression of great distances, give distant objects
a blue tint by using a light fog colored blue.
Layered Fog
In a mountain scene viewed from above, the valleys may be filled with fog
while the peaks are crystal clear. In fact, there may be several layers of fog
with clear air between them (see the following illustration).
Textures | 413
The AliasStudio system lets you create a one-dimensional table of values to
use for layered fog by using a column of data from a pix or mask file.
If you don't specify a file, a smooth ramp is used to create the fog. If you
specify a file, you may also specify a column, which indicates the horizontal
position for the column. By animating the column position between 0 and 1
(the left and right sides of the texture file), you can vary the layers of fog over
the duration of a scene. Use a file or ramp that has some variation across the
file. By taking advantage of the variations, fog layers can appear to move or
be made to appear and disappear. The height of the column corresponds to
values between AltitudeMin and AltitudeMax, the lower and upper boundaries
of the fog. Outside of this range, fog is assumed to be absent.
Argument
Name
Absolute
Range
Useful Range
Default
Description
amult
-infinity, infinity
-1, 1
1
Scaling factor
for layered fog
density
aoffset
-infinity, infinity
-1, 1
0
Offset factor
for layered fog
density
depth (triple)
0, infinity
0, 100
10, 10, 10
Decay constants for the
air
fog_color
(triple)
0, infinity
0, 255
255, 255,255
Colour constants for the
air
min_altitude
-infinity, infinity
-10, 10
0
Bottom of the
fog layer
max_altitude
-infinity, •
-10, 10
1
Top of the fog
layer
column
0, 1.0
0, 1
0.5
Animation key
to fog data
414 | Chapter 8 Procedural Textures and Natural Phenomena
density_file
no default
Mask file name
for 8-bit density image
fogtype =
012other
no fogconstant
foglayered
fogno fog
Bulge
The Bulge texture procedure was inspired by looking at windows on a
skyscraper. If a building was pumped full of air, the glass would bulge outwards
in the center while the edges would be constrained by the frame. The frame
of the window is exactly the same as a grid that is apparent when using the
bulge texture.
The Bulge texture procedure is most commonly applied as a bump map to
create a bulge effect on a surface. However, it can also be applied to a
transparency map to simulate windows that are dirty or opaque around the
edges but transparent in the middle area. When applied to a color map, there
is no apparent bulge, but this application can be used to simulate tile effects,
for example.
Argument
Name
Absolute
Range
Useful Range
Default
Description
uwidth
0.0, 1.0
0, 1
0.1
Width in u dir.
of constant
stripe
vwidth
0.0, 1.0
0, 1
0.1
Width in v dir.
of constant
stripe
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u dir. within
coverage area.
Textures | 415
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v dir. within
coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
416 | Chapter 8 Procedural Textures and Natural Phenomena
worldspace
TRUE FALSE
rotate
-infinity, infinity
mirror
TRUE FALSE
-360.0, 360.0
FALSE
flag to use
world space
texture mapping
0.0
angle coverage
area to be rotated
FALSE
flag to match
edges of texture
“Bulge” is a parametric texture.
Checker
The Checker texture procedure applies a colored checkerboard pattern to the
shader.
Argument
Name
Absolute
Range
Useful Range
Default
Description
contrast
-1.0, 1.0
-1.0, 1.0
1.0
Contrast for
the checker
pattern
color1 (triple)
0, infinity
0.0, 255.0
0,0,0
Color of one
set of checker
squares.
color2 (triple)
0, infinity
0.0, 255.0
0.0
Color of other
set of checker
squares.
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
within coverage area.
Textures | 417
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
418 | Chapter 8 Procedural Textures and Natural Phenomena
worldspace
TRUE FALSE
rotate
-infinity, infinity
mirror
TRUE FALSE
-360.0, 360.0
FALSE
flag to use
world space
texture mapping
0.0
angle coverage
area to be rotated
FALSE
flag to match
edges of texture
“Checker” is a parametric texture.
Cloth texture
The Cloth texture procedure is ideal for creating fabric-like textures and a
variety of other woven effects. In addition to being used as a simple
two-dimensional texture, the Cloth procedure is also effective with bump
mapping.
For very fine weaves, aliasing may be a problem, particularly when the cloth
is viewed from a distance. In this case, the cloth can be turned into a pix file
image by using the cloth texture as a Background Environment rather than
applying it to a shader. Once the background has been rendered, the resulting
pix file can then be applied to the shader as a file texture.
When applied to a bump map, the cloth texture generally produces better
effects when both thread colors are white and the gap color is black. The Color
Balance options are replaced by the Intensity options, Amult and Aoffset.
These options enable you to control the degree of the bump effect. Decreasing
the Blurmult value provides greater definition in the bump effect. Generally,
both the Amult and Blurmult values should be quite low, that is less than 0.1.
Argument
Name
Absolute
Range
Useful Range
Default
Description
u_thread_color
-infinity, infinity
0, 255
255.0, 255.0,
255.0
RGB value assigned to warp
of fabric
Textures | 419
v_thread_color
-infinity, infinity
0, 255
255.0, 0.0, 0.0
RGB value assigned to weft
of fabric
gap_color
-infinity, infinity
0, 255
0.0, 0.0, 0.0
RGB value assigned to area
between
threads
u_thread_width
0, 1
0, 1
0.75
Width of warp
threads
v_thread_width
0, 1
0, 1
0.75
Width of weft
threads
u_wave
-infinity, infinity
-0.5, 0.5
0.0
Wave pattern
of warp
v_wave
-infinity, infinity
-0.5, 0.5
0.0
Wave pattern
of weft
randomness
0, infinity
0, 1
0.0
Smears texture
in u,v.
width_spread
0, 1
0, 1
0.0
Subtracts a
random
amount off the
width of individual threads
brightness_spread
0, 1
0, 1
0.0
Subtracts a
random
amount off the
brightness
level of the
threads.
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
420 | Chapter 8 Procedural Textures and Natural Phenomena
within coverage area.
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
Textures | 421
U boundaries
of coverage
area.
worldspace
TRUE FALSE
rotate
-infinity, infinity
mirror
TRUE FALSE
-360.0, 360.0
FALSE
flag to use
world space
texture mapping
0.0
angle coverage
area to be rotated
FALSE
flag to match
edges of texture
File texture
The File texture procedure lets you use a pix file as a parametric texture on a
shader. Pix files are typically files created in AliasStudio or some other
compatible paint package, scanned images or previously rendered images.
The main new feature in v7 is the concept of a “super-texture”. This allows a
single File Texture to refer to a number of image files and the objects that use
those files. This is ideal for convert-solid-to-texture, where instead of creating
many shaders and textures, only one is created, but the texture points back
to the many different pix images. The parameters relevant to “super-texture”
are “object” and “object_image”.
The other important new feature is the “filter” option. This allows you many
ways to deal with the filtering/anti-aliasing of textures. A setting of 0 means
no filtering at all - this allows for exactly pixel-to-pixel match, less memory
used, faster rendering, but also may fall into danger of aliasing artifacts. A
setting of 1 results in exactly the same rendering as in version 6. For better
quality renderings, set the value to be > 1. As the value increases, the more
complicated the filter shape and thus the more expensive the rendering. The
optimal quality and speed combination would be to choose the quadratic
filter (3).
Argument
Name
Absolute
Range
Useful Range
Default
422 | Chapter 8 Procedural Textures and Natural Phenomena
Description
filter
0-5
filter_width
1
0 indicates no
filtering; 1 indicates blendfilter (only
choice in v6);
2 indicates
box-filter; 3 indicates quadratic filter; 4 indicates quartic
filter; 5 indicates gaussian
filter.
0.707
Filter width
that applies
only when “filter” > 1. The
larger the filter
width, the
more expensive the rendering.
image
string
Name of pix or
mask file to be
used for parametric texturing.
object
string
Name of object that the
super-texture
applies to.
object_image
string
Name of pix
image that the
object‘s supertexture applies
to.
Textures | 423
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
within coverage area.
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
424 | Chapter 8 Procedural Textures and Natural Phenomena
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
worldspace
TRUE FALSE
FALSE
flag to use
world space
texture mapping
rotate
-infinity, infinity
0.0
angle coverage
area to be rotated
mirror
TRUE FALSE
FALSE
flag to match
edges of texture
-360.0, 360.0
Grid
“Grid” is a parametric texture.
GridRGB generates a color grid pattern based on the surface u, v parameters.
The default case is white lines on a black background (filler). The "contrast"
variable controls the relative contrast of the line color to the filler color. A
"contrast" of 0.0 will set the color to the average of the line color and the filler
color. A "contrast" of -1.0 will swap the line color and the filler color.
Argument
Name
Absolute
Range
Useful Range
Default
Description
contrast
-1.0, 1.0
-1, 1
1.0
Relative contrast of the colors
uwidth
0, 0.5
0, 0.5
0.1
Width of lines
in the u direction
Textures | 425
vwidth
0, 0.5
0, 0.5
0.1
Width of lines
in the v direction
line_color
(triple)
0, infinity
0, 255
255.0
Line color
filler_color
(triple)
0, infinity
0, 255
0.0
Area between
lines color
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
within coverage area.
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
426 | Chapter 8 Procedural Textures and Natural Phenomena
vtranslate
-infinity, infinity
uwrap
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
worldspace
TRUE FALSE
FALSE
flag to use
world space
texture mapping
rotate
-infinity, infinity
0.0
angle coverage
area to be rotated
mirror
TRUE FALSE
FALSE
flag to match
edges of texture
-360.0, 360.0
Fractal
“Fractal” is a parametric texture.
The Fractal texture is a surface texture based on U, V parameter values and is
a random function that has a particular frequency distribution.
Fractals can be used for many different effects. A patch that is displacement
mapped with a fractal will resemble a piece of rock or a mountain. A surface
transparency mapped with a fractal will look like a piece of cloud or flame.
Textures | 427
Fractals are often used as part of more complex textures to create special effects
such as marble and wood.
Argument
Name
Absolute
Range
animated
TRUE FALSE
level_min
0, infinity
level_max
Useful Range
Default
Description
FALSE
Flag to use 3D
texture with u,
v, time rather
than 2D texture with just
u, v
0, 20
0.0
Minimum level
of iteration
0, infinity
0, 20
9.0
Maximum
level of iteration allowed
*time
0, infinity
0, 1
0.0
Time dimension for animated texture,
wraps for
range 0, 1
ratio
0, 1.0
0, 1
0.707
Fractal ratio
amplitude
0, infinity
0, 1
1.0
Amplitude of
fractal
threshold
0, 1
0, 1
0.0
Threshold for
fractal
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
within coverage area.
428 | Chapter 8 Procedural Textures and Natural Phenomena
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
Textures | 429
worldspace
TRUE FALSE
rotate
-infinity, infinity
mirror
TRUE FALSE
-360.0, 360.0
FALSE
flag to use
world space
texture mapping
0.0
angle coverage
area to be rotated
FALSE
flag to match
edges of texture
*The fractal will cycle as a function of time with period 1.
NOTE For textures that use Fractal, sFractal, sCloud, sMarble and Projection —
if both the min and max iteration values are very high (greater than 100), a render
can take a very long time. You cannot enter values over 100. Generally, if a finer
grained texture is desired, you may prefer to lower the blur, rather than increasing
the iteration count.
Mountain
“Mountain” is a parametric texture.
The Mountain texture procedure is used for rendering terrain. The Mountain
texture should first be applied to the shader as a Color Map, and then applied
again as a Displacement Map. The Color options have no effect on the
displacement map and relate only to the color map portion of the procedure.
All non-color related options are ignored for the color mapping when the
displacement map is applied. The color mapping automatically matches the
displacement mapping. The basis of the terrain model is a two-dimensional
fractal.
Argument
Name
Absolute
Range
Useful Range
Default
Description
amplitude
0, infinity
0, 1
1.0
Amplitude of
fractal
430 | Chapter 8 Procedural Textures and Natural Phenomena
rock_roughness
0, 1
0, 1
0.707
Fractal ratio for
the rock
level_max
0, infinity
0, 40
20.0
Maximum allowed iteration
level
snow_altitude
-infinity, infinity
-1, 1
0.5
Altitude for
snow
snow_dropoff
0, infinity
0, 10
2.0
Rate of dropoff
of snow with
altitude
snow_max_slope
0, infinity
0, 3
0.8
Slope above
which snow
does not stick
snow_roughness
0, 1
0, 1
0.4
Roughness of
snow
boundary_roughness
0, 1
0, 1
0.6
Raggedness of
edge of
rock/snow border
snow_color
(triple)
0, infinity
0, 255
255,255,255
Color of snow
rock_color
(triple)
0, infinity
0, 255
90, 110, 120
Color of rock
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
within coverage area.
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
Textures | 431
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
432 | Chapter 8 Procedural Textures and Natural Phenomena
worldspace
TRUE FALSE
rotate
-infinity, infinity
mirror
TRUE FALSE
-360.0, 360.0
FALSE
flag to use
world space
texture mapping
0.0
angle coverage
area to be rotated
FALSE
flag to match
edges of texture
Noise
*The noise function repeats cyclically as a function of time with period
1.0.“Noise” is a parametric texture.
Argument
Name
Absolute
Range
animated
TRUE FALSE
*time
-infinity, infinity
amplitude
threshold
Useful Range
Default
Description
FALSE
Flag to use 3D
texture with u,
v, time rather
than 2D texture with just
u, v
0, 1
0.0
Third dimension for animated texture,
wraps for
range 0, 1
-infinity, infinity
0, 1
1.0
Amplitude of
noise
0, infinity
0, 1
0.0
Additive value,
clips to 1.0
Textures | 433
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
within coverage area.
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
434 | Chapter 8 Procedural Textures and Natural Phenomena
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
worldspace
TRUE FALSE
FALSE
flag to use
world space
texture mapping
rotate
-infinity, infinity
0.0
angle coverage
area to be rotated
mirror
TRUE FALSE
FALSE
flag to match
edges of texture
-360.0, 360.0
Ramp
“Ramp” is a parametric texture.
The Ramp texture procedure is used to create a texture map that graduates
from one color to another or through a series of colors. Effects ranging from
simple stripes to geometric patterns and mottled surfaces are easily created by
the choice of Ramp and Interpolation types. By default, the Ramp texture
graduates from black to red to blue in a linear, horizontal (V ramp) fashion.
When applied to a Bump map however, the colors in the ramp are represented
as a gray scale.
The Ramp texture is commonly used as a two-dimensional Environment
background, but can also be used with other map types such as the
transparency map for special effects. When used as the source file for an
Environmental Sphere texture, you can create very natural-looking sky and
horizon effects. When used as the source file for a Projection texture, you can
create very natural woodgrain, marble and rock effects.
Argument
Name
Absolute
Range
Useful Range
Default
Description
Textures | 435
ramp_type
not applicable.
V_RAMPU_RAMPDIAGONALRADIALCIRCULARBOXUV_RAMPTARTANFOUR CORNER
V_RAMP
There are nine
different ramp
types to
choose from.
interpolation
not applicable
NONELINEAR_RAMPRAMP_UPRAMP_DOWNSMOOTHBUMP_OUTBUMP_IN
LINEAR_RAMP
Affects the way
colors in the
ramp are interpolated. There
are seven interpolation types
to choose
from, including a selection
for no interpolation, which
causes each
color to be displayed as a solid band.
ramp_color
-infinity, infinity
0, 256
0.0, 0.0, 0.0
Determines
the RGB value
of the ramp at
its given position
position
0, 1
0, 1
0.0
Gives the
placement of a
given ramp
color.
u_wave
-infinity, infinity
-0.5, 0.5
0.0
Controls the
amplitude of a
sine wave offset of the texture in the U
direction.
436 | Chapter 8 Procedural Textures and Natural Phenomena
v_wave
-infinity, infinity
-0.5, 0.5
0.0
Controls the
amplitude of a
sine wave offset of the texture in the V
direction.
noise
-infinity, infinity
0, 1
0.0
Affects the
amount that
the texture is
offset in the U
and V direction
by two-dimensional noise.
noise_frequency
-infinity, infinity
0, 1
0.5
Controls how
fine-grained
the noise is.
However, if the
U and V repeat
values of the
texture area
are greater
than 1, then
noise does not
cause a repeat
of the pattern.
hue_noise
-infinity, infinity
0, 1
0.0
Offsets the hue
value (mottles
the color).
sat_noise
-infinity, infinity
0, 1
0.0
Offsets the
“whiteness”
(creates a
weathered
look).
val_noise
-infinity, infinity
0, 1
0.0
Offsets the
“blackness.”
Textures | 437
hue_noise_frequency
-infinity, infinity
0, 1
0.5
Controls how
fine-grained
the hue noise
will be.
sat_noise_frequency
-infinity, infinity
0, 1
0.5
Controls how
fine-grained
the saturation
noise will be.
val_noise_frequency
-infinity, infinity
0, 1
0.5
Controls how
fine-grained
the value noise
will be.
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
within coverage area.
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
438 | Chapter 8 Procedural Textures and Natural Phenomena
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
worldspace
TRUE FALSE
FALSE
flag to use
world space
texture mapping
rotate
-infinity, infinity
0.0
angle coverage
area to be rotated
mirror
TRUE FALSE
FALSE
flag to match
edges of texture
-360.0, 360.0
Stencil
“Stencil” is a parametric texture.
The Stencil texture procedure is used mainly for label mapping purposes. Label
mapping is a two-dimensional texture that is usually applied as a Color map
onto a surface and often includes a transparency component to mask certain
Textures | 439
parts of the two-dimensional texture. An example of label mapping is consumer
packaging items such as a shampoo bottle with a label. The labels often hold
opaque colors combined with transparent areas. The Stencil texture procedure
enables you to easily place the two-dimensional label map and create the
necessary transparency mask.
Argument
Name
Absolute
Range
image_file
(string)
edge_blend
0, infinity
mask_file
(string)
mask_level
-infinity, infinity
Useful Range
Default
Description
name of the
pix file to be
used as a label
map
0, 1
0.0
Softens the
edges of the
texture coverage area. This
is useful for
hiding the texture boundary
when the mask
is not perfect.
name of the
mask file to be
used as a label
map
-1, 1
1.0
440 | Chapter 8 Procedural Textures and Natural Phenomena
Varies the degree of transparency of the
color areas. At
a value of 1
(the default),
all white areas
of the mask
are totally
transparent
and all black
areas are
totally opaque.
As you decrease the
value towards
0.00, the black
areas become
more transparent. By the
time you reach
0.00, no image transparency masking
occurs. If you
decrease the
mask_level to 1.00, the mask
is inverted,
where the
black areas become transparent and the
white areas are
opaque.
mask_blur
0, infinity
key_masking
ON, OFF
0, 0.25
0.0
Affects the
edges of the
mask. At a
value of 0.00,
there is no
mask blurring.
As you increase the blur
value, the
edges of the
mask are
blurred to produce soft edge
transparency
effects.
OFF
Toggle of color
key masking
Textures | 441
(mask derived
from a color).
Key masking
can be used in
combination
with a mask
file.
positive_key
ON, OFF
OFF
When ON, color determines
the visible portion of the texture. When
OFF, determines the hidden portions.
color_key
-infinity, infinity
0, 255
0.0, 0.0, 0.0
Color center to
key to.
hue_range
0, infinity
0, 1
0.5
Spread of hue
value from
central color
key.
sat_range
0, infinity
0, 1
0.5
Spread of saturation value
from central
color key.
val_range
0, infinity
0, 1
0.5
Spread of
brightness
value from
central color
key.
threshold
0, infinity
0, 1
0.5
Determines
sharpness of
mask boundary. At 0.0, all
values within
442 | Chapter 8 Procedural Textures and Natural Phenomena
the HSV
spread ranges
from the color
key are fully
masked. At 1,
the level of the
mask falls only
at the color
key, and drops
off to zero at
the HSV
spread limits.
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
within coverage area.
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
Textures | 443
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
worldspace
TRUE FALSE
FALSE
flag to use
world space
texture mapping
rotate
-infinity, infinity
0.0
angle coverage
area to be rotated
mirror
TRUE FALSE
FALSE
flag to match
edges of texture
-360.0, 360.0
Water
“Water” is a parametric texture.
The Water texture procedure is a parametric texture used to produce water
effects. If used as a Bump or Displacement map, the result resembles water
444 | Chapter 8 Procedural Textures and Natural Phenomena
waves or ripples. Water waves consist of linear sine waves, whereas water
ripples correspond to concentric rings originating from a drop.
Argument
Name
Absolute
Range
reflection_boundary
TRUE FALSE
umin
-infinity, infinity
umax
Useful Range
Default
Description
FALSE
Flag to reflect
ripples at reflection boundary
-5, 5
0.0
Extent of reflection boundary
-infinity, infinity
-5, 5
1.0
"""
vmin
-infinity, infinity
-5, 5
0.0
"""
vmax
-infinity, infinity
-5, 5
1.0
"""
ripple_drop_size
0, infinity
0, 1
0.3
Width before
drop off of envelope amplitude
ripple_frequency
0, infinity
0, 50
25.0
Number of
wavelengths of
modulated
sinewave per
unit length
ripple_phase_velocity
0, infinity
0, 10
2.5
Velocity of
modulated
sinewave
ripple_group_velocity
0, infinity
0, 10
1.0
Envelope velocity
Textures | 445
ripple_spread_start
0, infinity
0, 1
0.005
Spread of envelope at
ripple_time
zero
ripple_spread_rate
0, infinity
0, 1
0.3
Rate of spread
increase with
time
ripple_amplitude
-infinity, infinity
-1, 1
0.05
Amplitude
scaling factor
of ripple
ripple_u_origin
-infinity, infinity
0, 1
0.5
Start point position
ripple_v_origin
-infinity, infinity
0, 1
0.5
"""
ripple_time
-infinity, infinity
0, 100
0.0
Time variable
for concentric
waves
numwaves
0, infinity
0, 64
8
Number of linear waves
sub_frequency
0, infinity
0, 1
0.125
Frequency increment for
successive
waves
wind_u
-infinity, infinity
-5, 5
1.0
Wind direction
vector
wind_v
-infinity, infinity
-5, 5
0.0
"""
446 | Chapter 8 Procedural Textures and Natural Phenomena
frequency
0, infinity
0, 20
4.0
Wavenumber
of fundamental frequency
wave_velocity
0, infinity
0, 5
1.0
Velocity of fundamental frequency
wave_amplitude
-infinity, infinity
0, 1
0.05
Scaling factor
for wave amplitudes
smoothness
;0, infinity
0, 5
2.0
Rate of dropoff
of amplitude
with frequency
wave_time
-infinity, infinity
0, 10
0.0
Time variable
for linear
waves
urepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
u direction
within coverage area.
vrepeat
-infinity, infinity
-10.0, 10.0
1.0
# of copies in
v direction
within coverage area.
uoffset
-infinity, infinity
-1.0, 1.0
0.0
U offset repeat
within coverage area
voffset
-infinity, infinity
-1.0, 1.0
0.0
V offset repeat
within coverage area
Textures | 447
ucoverage
-infinity, infinity
0.0, 1.0
1.0
amount of U
surface to be
textured
vcoverage
-infinity, infinity
0.0, 1.0
1.0
amount of V
surface to be
textured
utranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of U
coverage area
to be moved.
vtranslate
-infinity, infinity
-1.0, 1.0
0.0
amount of V
coverage area
to be moved.
uwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
vwrap
TRUE FALSE
TRUE
flag to wrap
texture around
U boundaries
of coverage
area.
worldspace
TRUE FALSE
FALSE
flag to use
world space
texture mapping
rotate
-infinity, infinity
0.0
angle coverage
area to be rotated
mirror
TRUE FALSE
FALSE
flag to match
edges of texture
-360.0, 360.0
448 | Chapter 8 Procedural Textures and Natural Phenomena
About solid textures
Solid textures use the surface (x, y, z) point to reference into a three
dimensional space of texture values. However, the (x, y, z) point is not passed
directly to the table. It is first multiplied by a texture transformation matrix.
The default case is no specified texture transformation. In that case, the world
space surface point is used directly. If an object moves in world space it will
move through its solid texture. A wooden object would move through the
wood grain. While this may be desirable in certain animations, it is better to
have control over solid texture transformations.
If a transformation is to be used, it must be specified using the following
syntax.
In the DEFINITION section, the transformation must be declared using
transformation example;
Similarly, the transformation name must be included in the DEFINITION of
the texture being used. For example,
color=texture (procedure=Smarble,
transformation_name=example);
In the MODEL section, use
example = current_transformation( );
The assignment statement actually saves the current transformation in the
hierarchy. This means that if it is placed immediately before the piece of
geometry to be textured, the texture will stick to the geometry independent
of the transformation applied to the geometry. It is possible to transform the
texture in an arbitrary way by bracketing the assignment statement with its
own transformations, e.g.:
{
rotate (xaxis,25);
translate (10,5,2);
example = current_transformation ( );
}
NOTE:
1) The definition of the transformation must be BEFORE the definition of the
texture.
2) The assignment can be anywhere in the model section, either before or
after the patch.
About solid textures | 449
Also note that there is a similar function, current_position, which returns a
"triple" - very handy for fancy camera/spotlight motions.
Projection
“Projection” is a solid texture.
The Projection procedure can be thought of as the solid equivalent of a
two-dimensional texture.
A solid file texture can be extremely beneficial as it is not affected by the
parameterization of a surface. Therefore, a solid file texture is not prone to
the same distortion that can occur when mapping a surface texture to a surface
with uneven parameterization.
The projection procedure requires the input of a source texture (see How to
Use). Environment textures are not recommended as source textures for the
Projection procedure. Although the system will allow you to use Environment
textures, the results are likely to be unpredictable.
If the input source texture is a file, it can be projected in six different ways,
through the use of the Projection argument.
When the noise amplitude is set to 0, the image file specified is simply
projected through space. When the noise amplitude is not equal to 0, the
projection is perturbed with fractal noise (this takes much more time to render).
The Projection texture works in a similar fashion to sMarble and sWood: it
moves an image through space, creating a solid block with the image on it.
Therefore, if you want to create solid marble; and solid wood textures from
scanned-in images or painted pix files, you can create them using Projection.
Argument
Name
Absolute
Range
Useful Range
Default
Description
xmult
-infinity, infinity
-10, 10
1.0
Scaling factors
for extent of
pix file
ymult
-infinity, infinity
-10, 10
1.0
"""
xoffset
-infinity, infinity
-10, 10
0.0
Offsets for position of pix file
450 | Chapter 8 Procedural Textures and Natural Phenomena
yoffset
-infinity, infinity
-10, 10
0.0
""""
xamplitude
-infinity, infinity
0, 10
1.5
Amplitude of
noise function
for x direction
yamplitude
-infinity, infinity
0, 10
1.5
Amplitude of
noise function
for y direction
projection_type
triplanarcubicballcylindricalsphericalplanar
Projection type
used for mapping the solid
texture
xripples
0, infinity
0, 100
1.0
Fundamental
frequencies for
noise function
yripples
0, infinity
0, 100
1.0
""
zripples
0, infinity
0, 100
1.0
""
level_min
0, infinity
0, 50
0.0
Minimum allowed level of
iteration
level_max
0, infinity
0, 50
20.0
Maximum allowed level of
iteration
ratio
0, 1
0, 1
0.707
Ratio for fractal
noise
transformation_name
no default.
About solid textures | 451
Please note that X,Y, and Z refer to the height, width, and depth respectively
of the scene as it would appear in the FRONT window, regardless of coordinate
system.
Granite
The Granite solid texture is essentially the same as the Leather texture, with
the additional feature that three cell colors can be specified as opposed to only
one cell color in a Leather texture. The Granite texture is a simulation of three
different substances suspended in a medium.
Argument
Name
Absolute
Range
Useful Range
Default
Description
color1
-infinity, infinity
0 to 255
0.0, 0.0, 0.0
RGB value for
first granite
component.
color2
-infinity, infinity
0 to 255
140.0, 200.0,
100.0
RGB value for
second granite
component.
color3
-infinity, infinity
0 to 255
160.0, 210.0,
210.0
RGB value for
third granite
component.
filler_color
-infinity, infinity
0 to 255
150.0, 75.0,
50.0
Determines
the color of
the medium in
which the
spheres are
suspended.
cell_size
0, infinity
0 to 1
0.15
Determines
the general
size of the texture and is
equivalent to
scaling the texture DAG
node.
452 | Chapter 8 Procedural Textures and Natural Phenomena
density
0, infinity
0 to 1
1.0
Determines
the average
number of
spheres per
node of the 3D
lattice used in
the procedure.
The spheres
are fully
packed at a
density value
of 1.0.
mix_ratio
0, infinity
0 to 1
0.5
allows for the
three different
substances to
be mixed in
different proportions. At a
value of 0.0,
Color1 is the
highest in
terms of proportion to the
other two colors. At a value
of 0.5, Color2
is the highest
and at a value
of 1.0, Color3
is the highest.
spottyness
0, infinity
0 to 1
0.3
Determines
the randomization of the
general intensity of the
Cell_color. At
a value of 1.0,
the intensity is
fully random
(if the
About solid textures | 453
threshold parameter is set to
0.00).
randomness
0, infinity
0 to 1
1.0
The spheres or
cells are oriented in a regular 3D lattice
by default. The
position of the
spheres is perturbed by the
Randomness
value. At a
value of 1.0,
the sphere location is totally
random and at
a value of
0.00, the location of the
spheres is
totally regular.
threshold
0, infinity
0 to 1
0.5
Determines
the amount
that the three
colors used in
the procedure
mix into each
other. At a
threshold of
1.0, no mixing
occurs and the
spheres appear
as solid color
dots.
creases
0, 1 (OFF, ON)
OFF, ON
ON
Is actually an
option that
can be toggled
ON or OFF. If
454 | Chapter 8 Procedural Textures and Natural Phenomena
Creases is set
to ON, the
spheres don’t
mix with each
other. This creates boundaries like those
found in a collection of living cells. The
resulting texture has edges
that resemble
creases in
leather. If
creases is set
to OFF, the
spheres diffuse
uniformly into
each other and
no straight line
segments appear on the
resulting texture.
xripples
0, infinity
0, 100
1.0
Fundamental
frequencies for
noise function
yripples
0, infinity
0, 100
1.0
""
zripples
0, infinity
0, 100
1.0
""
level_min
0, infinity
0, 50
0.0
Minimum allowed level of
iteration
level_max
0, infinity
0, 50
20.0
Maximum allowed level of
iteration
About solid textures | 455
ratio
0, 1
0, 1
transformation_name
0.707
Ratio for fractal
noise
no default.
Leather
The Leather solid texture is ideal for creating a range of effects such as concrete,
Styrofoam and alligator skin, as well as leather. For many applications, a simple
pix file of leather will suffice for a good leather simulation. However, it is
sometimes nearly impossible to map a file texture to a surface without
distortions and discontinuities (mapping a simple two-dimensional file texture
to an automotive dashboard, for example). Worldspace texture mapping is
one solution to this problem, but it requires more effort and does not work
for all possible topologies. The procedural Leather texture overcomes these
problems by using a 3D noise of spheres to simulate a leather surface. This
texture is unlike leather in that real leather is a surface, and not a substance.
However, this texture can nicely simulate many types of animal skin,
particularly when used as a bump map.
If the surface is deformed during an animation (morphing), then the effect
will not be natural, as the surface will move through the solid texture.
The texture is made up of a collection of spheres suspended in a medium.
Argument
Name
Absolute
Range
Useful Range
Default
Description
cell_color
-infinity, infinity
0 to 255
95.0, 40.0,
15.0
Determines
the color of
the spheres
used in the
procedure.
crease_color
-infinity, infinity
0 to 255
60.0, 30.0, 0.0
Determines
the color of
the medium in
which the
spheres are
suspended.
456 | Chapter 8 Procedural Textures and Natural Phenomena
cell_size
0, infinity
0 to 1
0.5
Determines
the general
size of the texture and is
equivalent to
scaling the texture DAG
node.
density
0, infinity
0 to 1
1.0
Determines
the average
number of
spheres per
node of the 3D
lattice used in
the procedure.
The spheres
are fully
packed at a
density value
of 1.0.
spottyness
0, infinity
0 to 1
0.1
Determines
the randomization of the
general intensity of the
Cell_color. At
a value of 1.0,
the intensity is
fully random
(if the
threshold parameter is set to
0.00).
randomness
0, infinity
0 to 1
0.5
The spheres or
cells are oriented in a regular 3D lattice
by default. The
About solid textures | 457
position of the
spheres is perturbed by the
Randomness
value. At a
value of 1.0,
the sphere location is totally
random and at
a value of
0.00, the location of the
spheres is
totally regular.
threshold
0, infinity
0 to 1
0.83
Determines
the amount
that the two
colors used in
the procedure
mix into each
other. At a
threshold of
1.0, no mixing
occurs and the
spheres appear
as solid color
dots.
creases
0, 1 (OFF, ON)
OFF, ON
ON
If Creases is set
to ON, the
spheres don’t
mix with each
other. This creates boundaries like those
found in a collection of living cells. The
resulting texture has edges
that resemble
458 | Chapter 8 Procedural Textures and Natural Phenomena
creases in
leather. If
Creases is set
to OFF, the
spheres diffuse
uniformly into
each other and
no straight line
segments appear on the
resulting texture.
transformation_name
no default.
sCloud
The sCloud procedure is commonly used to create effects such as smoke and
steam in addition to clouds. The transparency level of the cloud area itself
can be interactively adjusted. The area surrounding the cloud is always
transparent, regardless of the type of mapping used.
sCloud requires that the geometry being textured is a sphere. The spheres can
be transformed in any way (for example, non-proportionally scaled), but the
actual base component must be a sphere. Any other geometry will give
unreliable and/or unpredictable results, although you are not prevented from
doing so.
When using sCloud for non-color mapping, it becomes a solid fractal texture
that has an added threshold depending on surface orientation.
As a surface curves into outline, the threshold is increased and added to the
fractal, the result is clipped to 1.0. If this technique is used to transparency
map ellipsoids (non-proportionally-scaled spherical patches), the results look
like puffs or clouds. If the texture is applied to non-ellipsoidal shapes, the
results will be of unreliable quality.
A series of nested ellipsoids; can be used to simulate fiery smoke. Each ellipsoid
is given a transparency map defined by sCloud. This procedure creates a fractal
with a slope-dependent offset added to it. This leads to an opaque center and
a ragged transparent edge. Each ellipsoid looks like a puff of smoke. The fire
effect is achieved by making the ellipsoids have different optical properties.
About solid textures | 459
The outer ellipsoid is made gray and dim. The inner ellipsoids are made
successively brighter and more orange.
Argument
Name
Absolute
Range
Useful Range
Default
Description
contrast
-1, 1
-1, 1
1.0
Relative contrast for color1
and color2
colour1 (triple)
0, infinity
0, 255
60, 0, 0
First color
colour2 (triple)
0, infinity
0, 255
255,255,255
Second color
transparency_range
0, infinity
0, 1
0.5
Transition
range for texture value
center_threshold
-infinity, infinity
-1, 0
0.0
Threshold
value for face
on surfaces.
edge_threshold
-infinity, infinity
1.0, 2.0
1.0
Threshold
value for outlines
soft_edges
TRUE FALSE
FALSE
Makes the texture color
blend to black
as surface tilts
away from eye.
Good for flame
effect when
used with incandescence
mapping on
ellipsoids. The
alpha channel
always does
this blending,
460 | Chapter 8 Procedural Textures and Natural Phenomena
regardless of
this flag.
amplitude
0, infinity
0-100
1.0
Noise amplitude
xripples
0, infinity
0, 100
1.0
Fundamental
frequencies for
noise function
yripples
0, infinity
0, 100
1.0
""
zripples
0, infinity
0, 100
1.0
""
level_min
0, infinity
0, 50
0.0
Minimum allowed level of
iteration
level_max
0, infinity
0, 50
20.0
Maximum allowed level of
iteration
ratio
0, 1
0, 1
0.707
Ratio for fractal
noise
transformation_name
no default.
“sCloud” is a solid texture.
NOTE sCloud requires that the geometry being textured is a sphere. The sphere(s)
may be transformed in any way, but the actual component(s) must be a sphere.
Any other geometry will give unreliable and unpredictable results.
About solid textures | 461
sFractal
sFractal is a solid fractal texture that returns a scalar value.
Argument
Name
Absolute
Range
Useful Range
Default
Description
threshold
0, 1
0, 1
0.0
Additive
threshold
xripples
0, infinity
0, 100
1.0
Fundamental
frequencies for
noise function
yripples
0, infinity
0, 100
1.0
""""
zripples
0, infinity
0, 100
1.0
""""
level_min
0, infinity
0, 50
0.0
Minimum allowed level of
iteration
level_max
0, infinity
0, 50
20.0
Maximum allowed level of
iteration
amplitude
-infinity, infinity
0, 1
1.0
Scaling factor
for noise before clipping
xripples
0, infinity
0, 100
1.0
Fundamental
frequencies for
noise function
yripples
0, infinity
0, 100
1.0
""
zripples
0, infinity
0, 100
1.0
""
462 | Chapter 8 Procedural Textures and Natural Phenomena
level_min
0, infinity
0, 50
0.0
Minimum allowed level of
iteration
level_max
0, infinity
0, 50
20.0
Maximum allowed level of
iteration
ratio
0, 1
0, 1
0.707
Ratio for fractal
noise
transformation_name
no default.
sRock
sRock is a simulation of particles suspended in a medium. “grain_size”
represents the particle size. “diffusion” controls the amount of mixing between
the particles and the medium. A diffusion of 0 will result in a sharp boundary
between the particles and the medium. A diffusion of 1.0 will result in a
complete blending. The variable “mix_ratio” controls the proportion of
particles to medium. If it is 1.0, the color is entirely color1; if it is 0, the color
is entirely color2. If sRock is applied as a bump map, then “mix_ratio” of 0.5
will result in even pits and bumps. If it is greater than 0.5, the surface will
have discrete bumps. If it is less than 0.5, the surface will have discrete pits
(depending on the parameterization of the surface).
If the surface is far enough from the eye that the grains become smaller than
pixel resolution, the blur effect will cause the texture to become a single color.
This is fine for color mapping, and helps to avoid aliasing problems. However,
if sRock is applied as a bump map, the surface will appear to become smooth
at large distances. A possible solution is to use an eccentric Blinn shader, which
mimics the microfacets of the bump map. If you want a video snow effect,
set the blur to 0.001 and the grain_size to 0.0001.
“sRock” is a solid texture.
Argument
Name
Absolute
Range
Useful Range
Default
Description
colour1 (triple)
0, infinity
0, 255
255,255,255
First color
About solid textures | 463
colour2 (triple)
0, infinity
0, 255
60,0,0
Second color
contrast
0-1
0-1
1.0
Controls contrast between
two colors
grain_size
0, infinity
0-0.1
0.01
Particle size
diffusion
0, infinity
0-1
1.0
Controls
amount of
mixing
between
particles and
the medium
mix_ratio
0-1
0-1
1.0
Controls the
proportion of
particles to
medium
transformation_name
no default.
Argument
Name
Absolute
Range
Useful Range
Default
Description
amplitude
-infinity, infinity
0, 10
1.5
Amplitude of
noise function
contrast
-1, 1
-1, 1
0.5
Contrast at
boundary
between vein
and filler
diffusion
0, infinity
0, 10
0.5
Degree of vein
diffusion into
filler material
464 | Chapter 8 Procedural Textures and Natural Phenomena
vein_width
0, 1
0, 1
0.1
Thickness of
vein material
filler_color
(triple)
0, infinity
0, 255
255,255,255
Color of filler
material
vein_color
(triple)
0, infinity
0, 255
76, 0, 0
Color of filler
material
xripples
0, infinity
0, 100
1.0
Fundamental
frequencies for
noise function
yripples
0, infinity
0, 100
1.0
""
zripples
0, infinity
0, 100
1.0
""
level_min
0, infinity
0, 50
0.0
Minimum allowed level of
iteration
level_max
0, infinity
0, 50
20.0
Maximum allowed level of
iteration
ratio
0, 1
0, 1
0.707
Ratio for fractal
noise
transformation_name
no default.
sMarble
“sMarble” is a solid texture.
Snow
The “Snow” texture varies the surface color based on the orientation of the
surface. With the default settings, the snow color will appear on the top of
About solid textures | 465
the object and the surface color will appear on the bottom. The rate at which
the snow color blends into the surface color is determined by the
“depth_decay” parameter. The threshold determines the maximum slope that
will hold snow. (Thicker snow is more opaque). The direction of the snow
(determined by wind in the real world) may be set by rotating the texture
placement icon, or in sdl by setting the “vector” parameter.
Fractal bump maps are useful in combination with snow because the snow
follows the bumping. This creates realistic snow effects by simulating the
clumping of snowflakes. Generally, the alpha mult and blur mult for the fractal
bump map should be low for best results.
It is useful also to make snow a transparency map on a white shader that is
then layered on other shaders in a scene. In this manner the snow can be
applied to all the objects in a scene. This also allows the snow to have its own
unique shading attributes. Note that the alpha mult should be -1.0 and the
alpha offset should be 1.0 for the snow transparency map.
Argument
Name
Absolute
Range
Useful Range
Default
Description
snow_color
0, infinity
0,255
255,255,255
Color of snow
surface_color;
0, infinity
0,255
128, 0, 0
Color of surface
contrast
0, 1
0, 1
1.0
Contrast
between surface and snow
color
threshold
0, 1
0, 1
0.5
Max slope for
snow
depth_decay
0, infinity
0, 10
5.0
Rate of transition between
snow and surface color
thickness
0, 1
0, 1
1.0
This determines the opa-
466 | Chapter 8 Procedural Textures and Natural Phenomena
city of the
snow
vector_x
-infinity, infinity
-1, 1
0.0
vector_y
-infinity, infinity
-1, 1
1.0
vector_z
-infinity, infinity
-1, 1
0.0
transformation_name
up vector for
snow
no default.
sWood
“sWood” is a solid texture.
Argument
Name
Absolute
Range
Useful Range
Default
Description
xmult
-infinity, infinity
-10, 10
1.0
Scaling factors
for extent of
pix file
ymult
-infinity, infinity
-10, 10
1.0
""""
xoffset
-infinity, infinity
-10, 10
0.0
Offsets for position of pix file
yoffset
-infinity, infinity
-10, 10
0.0
"""
xamplitude
-infinity, infinity
0, 10
0.1
Amplitude of
noise function
for x direction
About solid textures | 467
yamplitude
-infinity, infinity
0, 10
0.1
Amplitude of
noise function
for y direction
center_u
-3,3
-3,3
0.5
Origin for
growth of ring
layers
center_v
-3, 3
-3, 3
0.5
“““
grain_contrast
0, 1
0, 1
1.0
Contrast
between vein
and wood color
grain_spacing
0, 1
0, 1
0.01
Spacing of
grain dots
grain_color
(triple)
0, infinity
0, 255
30, 10, 0
Color of the
grain
filler_color
(triple)
0, infinity
0, 255
210,160,120
Color of the
filler part
between rings
vein_color
(triple)
0, infinity
0, 255
40, 20, 10
Color of the
vein part of
rings
vein_spread
0, infinity
0, 3
0.25
Diffusion of
vein color into
the rings
layer_size
0, infinity
0, 0.5
0.02
Mean spacing
between rings
randomness
0, 1
0, 1
0.5
Degree of randomization of
layers
468 | Chapter 8 Procedural Textures and Natural Phenomena
age
0, infinity
0, 100
20.0
Time in years
for ring layer
thickness to
reach maximum
xripples
0, infinity
0, 100
1.0
Fundamental
frequencies for
noise function
yripples
0, infinity
0, 100
1.0
""
zripples
0, infinity
0, 100
1.0
""
level_min
0, infinity
0, 50
0.0
Minimum allowed level of
iteration
level_max
0, infinity
0, 50
20.0
Maximum allowed level of
iteration
ratio
0, 1
0, 1
0.707
Ratio for fractal
noise
transformation_name
no default.
Volume
The Volume procedure allows the system to interpret multiple pix files in a
sequence as a volume of pixels. When an object is assigned a shader with its
color set to a volumetric texture, and “mapping” is set to “volumetric,” the
object will appear to cut through a cube formed by stacking the pix files up.
X, Y, and Z on the surface are mapped to U,V, and pixfile number. The size
of the cube is defined by the texture transform.
When used as a subtexture of the “Ball” texture, “mapping” should be set to
“directional.” In this case, the pix file sequence should be set to a sequence
About solid textures | 469
of ball images photographed from equal angles around the ball. The volume
then maps U,V, View_Direction to U,V, Pixfile number.
Argument
Name
Absolute
Range
Useful Range
Default
Description
from
1-1024
1-1024
1
The extension
number of the
first pix file in
the sequence
of pix files that
makes up the
pixel volume
to
1-1024
1-1024
1
The extension
number of the
last pix file in
the sequence
of pix files that
makes up the
pixel volume.
pix_sequence
---
---
---
The name of
the first pix file
of the sequence of pix
files that make
up the pixel
volume.
mapping
directional,
volumetric
directional,
volumetric
470 | Chapter 8 Procedural Textures and Natural Phenomena
The method
by which UV
or XYZ parameters are
mapped onto
pixel values for
the pixel
volume.
xripples
0, infinity
0, 100
1.0
Fundamental
frequencies for
noise function
yripples
0, infinity
0, 100
1.0
""
zripples
0, infinity
0, 100
1.0
""
level_min
0, infinity
0, 50
0.0
Minimum allowed level of
iteration
level_max
0, infinity
0, 50
20.0
Maximum allowed level of
iteration
ratio
0, 1
0, 1
0.707
Ratio for fractal
noise
transformation_name
no default.
About environment maps
An environment map is a model of the world as seen from a particular point
of view over a viewing angle of 360 degrees. In AliasStudio, environment maps
may be used for two things. For reflection mapping, the environment map is
used to store a model of the world around a particular point inside or near a
surface. This map is then used to compute the color of a ray reflected by that
surface. In this way, convincing reflection effects may be produced.
The syntax for using an environment map to do reflections is as follows. In
the DEFINITION section use the following statement as part of a texture on
a shader:
reflection = texture (procedure = name,
arg 1 = value 1,
arg 2 = value 2,
etc. ...);
About environment maps | 471
The second application of environment maps is to create backgrounds. Since
an environment map stores a complete view of the world in all directions,
any particular view may be computed efficiently. This will only be accurate
if the environment map was created around the current eye point. There are
several reasons to do this.
First, the environment may be procedural in nature and this is the only way
to see it. The "sky" procedure is a good example of this case. Secondly, a scene
may be largely static but also very expensive to render. In that case a fast
method for animating the camera direction without re-rendering the scene
for every frame would be desirable. Moving objects could then be rendered
over the top. The "Cube" procedure would be ideal for this approach. The
syntax for creating a background from an environment map is as follows. In
the ENVIRONMENT section use:
background = texture (procedure = name,
arg 1 = value 1,
arg 2 = value 2,
etc. ...);
An environment map exists in an environment space coordinate system. The
default for all environments in AliasStudio is to have the environment space
aligned with world space. Certain applications require the ability to rotate the
environment map relative to world space. In particular, an object, lights and
camera may be fixed relative to each other and the environment map tumbled.
The syntax for this is identical to the coordinate transformations used with
solid textures.
For example, consider a surface that is a ball being rendered with reflection
mapping. It needs to have a transformation associated with it.
In the DEFINITION section the transformation must first be declared.
transformation ball;
A subsequent shader will include a textured parameter with
“transformation_name”
reflection = texture (procedure = Chrome,
transformation_name= ball),
In the MODEL section the statement
ball = current_transformation ( );
will appear.
If it is located at the base of the hierarchy then the reflection map will be
unaffected since the default is for the environment map to be aligned with
472 | Chapter 8 Procedural Textures and Natural Phenomena
world space anyway. However, if the assignment of the
“current_transformation” to “ball” appears within a hierarchy, the
environment map will rotate with the hierarchy. So, if the assignment occurs
just before a patch statement the environment map will rotate with the patch.
If a non-proportional scale is applied, the environment map will be stretched
and distorted.
NOTE It is important to note that Ball, Chrome, Cube, Sphere and Sky should not
be used for bump or displacement mapping. The basic nature of environment
mapping precludes accurate calculations. Although the system will allow it, you
will be warned that the results will be unreliable and unpredictable.
Ball
The Ball procedure maps photographs of reflective balls into 3D environments.
This texture is designed primarily to accompany a pix file background. If you
take a photograph at a desired location and camera view for a scene, a reflective
sphere is then placed in the scene at the location where you wish to view your
model. The photo of the ball is essentially a sample of the total environment.
It contains a full 360 degree field of view, minus the portion directly behind
the ball. The highest resolution is in the direction of the camera, therefore
providing the best compression of data for that point of view.
The Ball procedure has optional planes and a finite sphere to assist in modeling
the geometry of the environment. An eyespace toggle is provided to simplify
placement when a background pix file is used. In addition, a reflection toggle
can be used to help in advanced modeling of background geometry.
Argument
Name
Absolute
Range
Useful Range
image
Default
Description
no default
Name of pix
file for reflection maps
inclination;
-infinity, infinity
-180, 180
0
Angle of camera with walls
elevation
-infinity, infinity
-90, -90
0
Angle of Camera with floor
About environment maps | 473
eyespace
ON OFF
OFF
When ON, the
reflections will
match the
background
pix, regardless
of the camera
location.
sky_radius
0, infinity
0, 50
0
Radius of intersection sphere
top
0, infinity
0, 50
0
Distance of intersection
planes from
origin
bottom
0, infinity
0, 50
0
Distance of intersection
planes from
origin
left
0, infinity
0, 50
0
Distance of intersection
planes from
origin
right
0, infinity
0, 50
0
Distance of intersection
planes from
origin
front
0, infinity
0, 50
0
Distance of intersection
planes from
origin
back
0, infinity
0, 50
0
Distance of intersection
planes from
origin
474 | Chapter 8 Procedural Textures and Natural Phenomena
reflect
ON OFF
ON
If set to OFF,
ball behaves
like a solid texture
Chrome
The Chrome texture creates a simple but effective environment to emit
convincing reflections. The basic environment map consists of a ground plane
and a sky plane. To add visual complexity to the scene, a series of rectangular
lights are included in the sky. These lights are for visual effect only and do
not act as light sources.
There is no blurring capability for the Chrome procedure, so aliasing artifacts
may appear on reflective surfaces. These may be greatly reduced by having an
aalevel of 4 and an aathreshold of 0 when rendering. An alternative is to use
Chrome to create the faces for the Cube procedure.
Argument
Name
Absolute
Range
Useful Range
Default
Description
floor_color
(triple)
0, infinity
0, 255
150,150,200
Color straight
down as seen
from front window
horizon_color
(triple)
0, infinity
0, 255
0, 0, 0
Color just below the horizon
sky_color
(triple)
0, infinity
0, 255
200,200,250
Color just
above horizon
zenith_color
(triple)
0, infinity
0, 255
100,100,250
Color straight
up along +y
light_color
(triple)
0, infinity
0, 255
250, 250, 250
Color of lights
in the sky
About environment maps | 475
light_width
0, infinity
0, 10
1.0
Number of
lights per unit
length along
width
light_width_mult
0, 1.0
0, 1.0
1.0
Multiplier for
light width
light_width_offset
0, 1.0
0, 1.0
1.0
Offset for light
width
light_depth
0, infinity
0, 1.0
1.0
Number of
lights per unit
length along z
light_depth_mult
0, 1.0
0, 1.0
1.0
Multiplier for
light depth
light_depth_offset
0, 1.0
0, 1.0
0.0
Offset for light
depth
grid_color
(triple)
0, infinity
0, 255
0, 0, 0
Grid line color
grid_width
0, infinity
0, 10
1.0
Number of
grid cells per
unit length
along x
grid_width_mult
0, 1.0
0, 1.0
1.0
Multiplier for
grid width
grid_width_offset
0, 1.0
0, 1.0
0.0
Offset for grid
width
grid_depth
0, infinity
0, 10
1.0
Number of
grid cells per
unit length
along z
476 | Chapter 8 Procedural Textures and Natural Phenomena
grid_depth_mult
0, 1.0
0, 1.0
1.0
Multiplier for
grid depth
grid_depth_offset
0, 1.0
0, 1.0
0.0
Offset for grid
depth
real_floor
TRUE FALSE
0, 1
0
Flag for presence of real vs
angular floor
floor_altitude
-infinity, infinity
-100, 100
-1.0
Elevation of
floor along the
y-axis
“Chrome” is an environment texture.
Sphere
A Sphere environment texture uses a single image to store the intensity
information for all possible directions. However, in order to create the spherical
map, the system actually uses a square texture map. If you consider wrapping
a square texture map onto a sphere, you will see an immediate problem; you
can’t wrap a whole square onto a sphere and have the side edges match without
either shrinking the square image vertically or having a lot of overlap at the
poles. This is because the texture map goes 360 degrees around the sphere at
the sides, but vertically it only covers the sphere from pole to pole, which is
180 degrees. To overcome this problem, the middle half of the square texture
map is used and the information of the top and bottom 1/4 of the map is
discarded, as shown in the following illustration.
About environment maps | 477
The best way to create a spherical environment map is to generate a ramp
image and then paint objects onto it that avoid the poles and the edges.
Consider the case of the default transformation and an eye point on the
positive x-axis looking at the origin. If the spherical environment map is used
directly as a background, the edge join will be visible. However, if a surface is
viewed that has been reflection mapped, the join will be behind the surface
and hardly visible.
Also consider the resolution of spherical reflection maps and how crisp they
will appear. The horizontal resolution corresponds to 360 degrees. A 5122
image will have one pixel every 1/2 degree. Flat surfaces that are reflection
mapped will appear as blurred indistinct reflections. Higher resolution images
may be used, but they are difficult to paint and use a lot of memory. It is better
to use rounded geometry instead.
Argument
Name
Absolute
Range
Useful Range
image
flip
0, 1
shear_v
-infinity, infinity
-5, 5
Default
Description
no default
Name of pix
file for reflection maps
0
Flag to indicate whether to
swap u, v
0.0
Change of u
for change in v
478 | Chapter 8 Procedural Textures and Natural Phenomena
shear_u
-infinity, infinity
-5, 5
source_texture
0.0
Change of v
for change in u
no default
Texture to be
used as the image
“Sphere” is an environment texture.
Cube
The procedure “Cube” is an environment map defined by six faces of a cube.
These faces are just square texture images in the form of pix files. Each file
corresponds to a perspective view with a field of view of 90 degrees with a
view direction along the positive and negative x, y, z axes. These images can
be painted or digitized. However, the real application of cubic reflection maps
is using rendered images. It is possible to construct an environment map about
a particular point in a scene merely by using a few lines of SDL.
For the origin point 0.0 0.0 0.0 use the following statements:
In the DEFINITION section:
startframe = 1;
endframe = 6;
triple camera_view(0.0, 0.0, 0.0);
In the MODEL section use:
if ( frame == 1.0 ) camera_view = (1.0, 0.0, 0.0);
else if (frame == 2.0 ) camera_view = (-1.0, 0.0, 0.0);
else if (frame == 3.0 ) camera_view = (0.0, 1.0, 0.0);
else if (frame == 4.0 ) camera_view = (0.0, -1.0, 0.0);
else if (frame == 5.0 ) camera_view = (0.0, 0.0, -1.0);
else if (frame == 6.0 ) camera_view = (0.0, 0.0, -1.0);
camera (eye = (0,0,0), view = camera_view, fov = 90,
viewport = (0.0, 255.0, 0.0, 255.0),
aspect = (1.0)
);
For further information on creating cubic environment maps, please refer to
the Cubic Environment Tutorial.
“Cube” is an environment texture.
About environment maps | 479
Cubic environment maps are very fast to reference so they are the preferred
method for animation sequences. The same scene may render 3 or 4 times
faster using a cubic reflection map in place of the Sky procedure. It is possible
to use other environment maps to create cubic environment maps merely by
rendering them as backgrounds. It is, of course, not worth doing if the
environment such as Sky varies every frame. However, if the environment is
static for many frames, the speed savings will be considerable.
Cubic environment maps have the advantage that they may be blurred by an
arbitrarily large amount without any additional cost. When generating a
background from an environment map the amount of blurring required to
prevent aliasing increases with the field of view. In practice, with 5122 texture
images and a field of view less than 90 degrees this will result in very little
required blurring. For reflection mapped surfaces, however, the amount of
blurring will depend upon the surface curvature and the distance from the
eye point. Currently, this is not computed automatically. However, the variable
"bluroffset" will allow the user to defocus the reflections by a desired amount.
In fact, soft focus reflections can be used to simulate less than perfectly polished
surfaces.
Argument
Name
Absolute
Range
Useful Range
Default
Description
top
no default
Pix file name
for top image
bottom
no default
Pix file name
for bottom image
right
no default
Pix file name
for right image
left
no default
Pix file name
for left image
front
no default
Pix file name
for front image
back
no default
Pix file name
for back image
480 | Chapter 8 Procedural Textures and Natural Phenomena
In y-up systems, these are relative to the view down the z-axis; in z-up systems,
they are relative to the view down the y-axis.
Sky
The Sky procedure is an environment map that generates images of a planetary
atmosphere as seen from the surface of the planet. Parameter sets enable you
to control the composition of the atmosphere and the cloud layer. If no floor
is specified, the environment below the horizon is a vertical mirror reflection
of the environment above the horizon. If a floor is specified, it must be given
an altitude and other variables to control the positioning of a color pix file
texture map on the surface.
Argument
Name
Absolute
Range
Useful Range
Default
Description
floor_texture
no default
pix file name
for floor texture 24 bits
cloud_texture
no default
Mask file name
for cloud texture 8 bits
cloud_altitude
0, 1
0, 0.5
y coordinate of
cloud layer as
a fraction of
sky_thickness
(if Y-up)
space_samples
0, infinity
1, 10
5.0
# of samples
above clouds
floor_samples
0, infinity
0, 3
1.0
# of samples in
front of floor
cloud_samples
0, infinity
0, 3
5.0
#. of samples
below clouds
About environment maps | 481
air_density
0, infinity
0, 10
1.0
Density of air
molecules
dust_density
0, infinity
0, 3
0.0
Density of dust
particles
sun_azimuth
-infinity, infinity
0, 360
145.0
Rotation of sun
vector about
vertical vector
sun_elevation
-infinity, infinity
-10, 90.0
45.0
Angle of elevation of sun
vector relative
to floor
sun_size
0, infinity
0, 30
0.531
Radius of sun's
disc in degrees
sun_blur
0, infinity
0, 50
1.0
Radius of halo
around sun in
degrees
sun_halo_brightness (triple)
0, infinity
0, 1
0.2,0.3,0.2
Multiplicative
color for halo
around the sun
sky_brightness
(triple)
0, infinity
0, 10
1.0, 1.0, 1.0
Multiplicative
color for the
sky
sun_brightness
(triple)
0, infinity
0, 10
1.0, 1.0, 1.0
Multiplicative
color for the
sun
floor_altitude
-infinity, infinity
-100, 100
-1.0
y coordinate of
the floor (if yup)
482 | Chapter 8 Procedural Textures and Natural Phenomena
cloud_density
0, infinity
0, 5
1.0
Density of the
sky
cloud_radius
0, infinity
0, 50
20.0
Radius of halo
around sun
cloud_width_mult
-infinity, infinity
-0.2, 0.2
0.1
Scaling factors
for cloud map
position on
floor
cloud_depth_mult
-infinity, infinity
-0.2, 0.2
0.1
"""
cloud_blurmult
0, infinity
0, 10
1.0
Scaling factor
for cloud blur
size
cloud_bluroffset
0, infinity
0, 1
0.0
Offset for
cloud blur size
cloud_threshold
0, infinity
0, 1
0.5
Threshold for
presence of
clouds
cloud_brightness
0, infinity
0, 10
1.0, 1.0, 1.0
Multiplicative
color for ambient cloud illumination
cloud_sunset_brightness
0, infinity
0, 500
300, 300, 300
Multiplicative
color for front
lighting
cloud_power
0, 1
0, 1
1.0
Exponent for
cloud density
falloff
About environment maps | 483
floor_width_mult
-infinity, infinity
0, 10
1.0
Scaling factors
for color map
position on
floor
floor_depth_mult
-infinity, infinity
0, 10
1.0
""""
floor_width_offset
-infinity, infinity
0, 1
0.0
Offsets for color map position on floor
floor_depth_offset
-infinity, infinity
0, 1
0.0
""""
floor_blurmult
0, infinity
0, 10
1.0
Scaling factor
for floor blur
size
floor_bluroffset
0, infinity
0, 1
0.0
Offset for floor
blur size
floor_color
(triple)
0, infinity
0, 255
255, 255, 255
Color of floor
sky_radius
0.01, infinity
0.01, 300
50.0
Radius of planet as a multiple
of sky_thickness
sky_thickness
1, infinity
100, 10000
1000
Thickness of
atmosphere
total_brightness
0, infinity
0, 10
1.0
Scales the
overall brightness of environment
484 | Chapter 8 Procedural Textures and Natural Phenomena
has_floor
TRUE FALSE
TRUE
Flag setting
whether or not
a floor is used.
“Sky” is an environment texture.
About environment maps | 485
486
Tutorials
9
Creating Rendered Cubic Environment Maps
Cubic environment maps provide a fast and attractive way to simulate a
one-bounce ray trace. The object to which a cubic environment (sometimes
called a cubic reflection) map is applied, appears to reflect its environment. This
tutorial will demonstrate a method for creating cubic environment maps for
two types of reflections. The first will show how to create the reflection map
for a non-planar object in the scene, and the second will show how to create a
reflection map for a reflective plane (i.e., a floor or a wall).
Road Map
The basic steps involved in creating the reflection map files are as follows:
1 Copy the original SDL file to a different “special” SDL file.
2 Edit the special SDL file, remove the object that we are creating the
reflection map for.
3 Change the name of the output file.
4 Change the eye position, twist, fov, resolution and aspect ratio
5 Add the animation of the view direction
6 Finish editing the special SDL file.
7 Render the special SDL file.
8 Edit the original SDL file to add the reflection map to the proper shader.
9 Render the original SDL file.
487
Reflection Map for a Non-planar Object in the Scene
A cubic environment map requires six pix files that show what is seen along
each of the positive and negative axes directions from a spiced point. It is the
specification of the point that allows us to create the reflection map for certain
types of reflections.
Let us assume that we want to render a cubic reflection map for a sphere that
is inside a room:
Sphere to be reflection mapped
In order to create a reflection map of what is seen from the sphere, we must
create a special SDL file. This file will have an eye point positioned at the
centre of the sphere (or at the center of whatever object we want). This file
will NOT contain the sphere, however. This is because if the sphere were in
the SDL file, when we render from the centre of the sphere all we will see is
the inside of the sphere and not what is around the sphere (its environment).
It is important to always remove the object that we are creating the
environment map for from this special SDL file.
Once the eye point is placed at the centre of the object, and that object is
removed from this special SDL file, we must insert the animation statements
for the eye direction.
Let us assume that the centre of our sphere (and thus, our eye) is at (0, 0, 0).
The first thing we do is remove the “view” statement from the MODEL section
and replace it with a new camera. It is very important to change the field’s
fov to 90.0, twist to 0.0, and aspect to 1.0. Our camera section now looks like:
488 | Chapter 9 Tutorials
camera (eye = (0, 0, 0),
view = camera_view,
fov = 90,
viewport = (0.0, 255.0, 0.0, 255.0),
aspect = (1.0)
);
In order to use this camera, it must be defined in the DEFINITION section:
triple camera_view (0.0, 0.0, 0.0);
In order to create the pix files from this little animation, the DEFINITION
section must include:
startframe = 1;
endframe = 6;
It is also important to remember that we are creating pix files that are to be
used as texture maps, so the resolution should be one of 256, 512, 1024, etc.
The final step is to add animation to the MODEL section, also as described in
this manual:
if (
else
else
else
else
else
frame == 1.0
if (frame ==
if (frame ==
if (frame ==
if (frame ==
if (frame ==
) camera_view = (1.0, 0.0, 0.0);
2.0 ) camera_view = (-1.0, 0.0, 0.0);
3.0 ) camera_view = (0.0, 1.0, 0.0);
4.0 ) camera_view = (0.0, -1.0, 0.0);
5.0 ) camera_view = (0.0, 0.0, -1.0);
6.0 ) camera_view = (0.0, 0.0, 1.0);
After rendering this special SDL file, we return to the original SDL file and add
the reflection map to the shader that corresponds to the object (in this case,
a sphere).
Creating Rendered Cubic Environment Maps | 489
shader AAA ( model = phong,
diffuse = 0.800000,
shinyness = 10.000000,
color = (0.0, 0.0, 0.0),
specular = (0.800000, 0.800000, 0.800000),
reflectivity = 1.0,
reflection = texture(procedure = Cube,
right = "pix/special.1",
left = "pix/special.2",
top = "pix/special.3",
bottom = "pix/special.4",
front = "pix/special.6",
back = "pix/special.5"
)
);
The sphere will now have a reflection of the environment on it.
Reflection Map for a Reflective Plane
The first section described how to create and use a reflection map for an object
in the scene. Creating reflection maps for planar objects (say a shiny floor) is
done in a different manner.
Creating a reflection map for a planar object is easiest if the planar object lies
on one of the XY, YZ, or XZ planes. If this is not the case, then calculation of
the eye point for the special SDL file is difficult, but it can still be done.
Let’s start with the simplest case. We have a planar object that lies on the XZ
plane (see below). For simplicity, we will refer to this planar object as the floor
of our modeled room, in a Y-up environment.
Reflection map for planar object
490 | Chapter 9 Tutorials
What we will do, in effect, is mirror our eye point in the floor. The equation
to do this mirroring for the example above is:
eye_Y' = floor_y – (eye_y – floor_y) (1)
Substituting in our values from the example and solving:
eye_Y' = 2.0 – (5.0 – 2.0)
eye_Y' = 2.0 – (3.0)
eye_Y' = –1.0
So, in our special SDL file, we change only the eye’s Y value to be this new Y'
value. We then replace the “view” statement with a new view statement as
with the first example. For example, if the CAMERA section was
Camera (
eye = (3.0, 5.0, –2.0),
view = (0.3, 1.2, 9.3),
fov = 40.0,
aspect = 1.316
);
then we would change it to
camera (
eye = (3.0, -1.0, –2.0),
view = camera_view,
fov = 90,
viewport = (0.0, 255.0, 0.0, 255.0),
aspect = (1.0)
);
and, as before, we would change the output pixel resolution to one of 256,
512, 1024, 2048, etc., and add the animation to the MODEL section for x_dir,
y_dir, and z_dir. This special SDL file is rendered and the reflection map is
applied to the floor’s surface descriptor in the original SDL file. Remember to
remove the floor in the special SDL.
If the planar object is not on the XZ plane, then the modified coordinate can
be found by substitution of X for Y in equation (1) if the object lies in the YZ
plane or by substituting Z for Y in equation (1) if the object lies in the XY
plane.
If the planar object does not lie in one of the above planes, then it becomes
more difficult to calculate the new eye point, and it requires a lot more math.
Let’s say that our planar object is described as a face that has the following
points in the SDL file:
Creating Rendered Cubic Environment Maps | 491
XYZ
V1 –0.4183 –4.64 2.5132
V2 –3.905 –1.084 2.5716
V3 0.114 3.2474 –1.6657
V4 4.1738 –0.3513 –2.0018
And assume that the eye is at (0.5, 0.5, 12).
Now, in order to reflect the eye point in this plane, we will need a normal to
this plane. To calculate the normal, we need 3 of the vertices of the planar
object. Let us arbitrarily choose V1, V2 and V3, which from inspection of the
wire frame, we know do not lie in a straight line (in mathematical terms, the
points are not co-linear).
DX2 = V2.X – V1.X (2)
DX3 = V3.X – V1.X (3)
DY2 = V2.Y – V1.Y (4)
DY3 = V3.Y – V1.Y (5)
DZ2 = V2.Z – V1.Z (6)
DZ3 = V3.Z – V1.Z (7)
The results of equations (2) through (7) are then used to compute:
L = DY2 *DZ3 – DY3 * DZ2 (8)
M = DX3 * DZ2 – DX2 * DZ3 (9)
N = DX2 * DY3 – DX3 * DY2 (10)
R = L * L + M * M + N * N (11)
R = SQRT(R) (12)
L = L/R (13)
M = M/R (14)
N = N/R (15)
P = L * V1.X + M * V1.Y + N * V1.Z (16)
Now, you might think that all of that is far too much math for one day, but
we’re not done yet. (SQRT(R) in equation (12) means that we want the square
root of the number represented by R.)
The distance of the eye point from this plane is calculated by:
492 | Chapter 9 Tutorials
D = L * EYE_X + M * EYE_Y + N * EYE_Z + P (17)
If D is negative, then the new eye point is given by:
D = 2 * (–D)
EYE_X' = EYE_X + D * L (18)
EYE_Y' = EYE_Y + D * M
EYE_Z' = EYE_Z + D * N
If D is positive, then the new eye point is given by:
D=2*D
EYE_X' = EYE_X + D * (–L) (19)
EYE_Y' = EYE_Y + D * (–M)
EYE_Z' = EYE_Z + D * (–N)
If D turns out to be equal to 0.0, then the eye point is on the plane and you
should not create a reflection map for this object, because a mirror viewed
“side on” does not reflect anything.
Returning to our example and placing the values into equations (2) through
(7) we get:
DX2 = –3.905 – –0.4183 = -3.4867
DX3 = 0.114 – –0.4183 = 0.5323
DY2 = –1.084 – –4.64 = 3.556
DY3 = 3.2474 – –4.64 = 7.8874
DZ2 = 2.5716 – 2.5132 = 0.584
DZ3 = –1.6657 – 2.5132 = –4.1789
Placing these values into equations (8) through (10) we get:
L = 3.556 * –4.1789 – 7.8874 * 0.584 = -19.46641
M = 0.5323 * 0.584 – –3.4867 * –4.1789 = –14.2597
N = –3.4867 * 7.8874 – 0.5323 * 3.556 = –29.39385
Using these values in equations (11) and (12) we get:
R = –19.46641 * –19.46641 + –14.2597 * –14.2597 + –29.39385 * –29.39385
= 1446.27858
R = SQRT (1446.27858) = 38.02997
Creating Rendered Cubic Environment Maps | 493
Then applying equations (13) to (15) we get:
L = –19.46641/38.02997 = –0.51187
M = –14.2597/38.02997 = –0.37496
N = –29.39385/38.02997 = –0.77291
Then we take a break to catch our breath and continue by applying equation
(16) to these numbers:
P = –0.51187 * –0.4183 + –0.37496 * –4.64 + –0.77291 * 2.5132 = 0.011452
After applying equation (17) we get:
D = –0.51187 * 0.5 + –0.37496 * 0.5 + –0.77291 * 12.0 + 0.011452 = –9.70688
We can see that D is negative, so we apply equation (18):
D = 2 * (– –9.70688) = 2 * 9.70688 = 19.41376
Note that the negative of a negative number is a positive number, and continue
with equation (18):
EYE_X' = 0.5 + 19.41376 * –0.51187 = –9.43732
EYE_Y' = 0.5 + 19.41376 * –0.37496 = –6.77938
EYE_Z' = 12.0 + 19.41376 * –0.77291 = –3.0051
Now that we have our new eye point, we go back to our special SDL file, and
replace all three eye components:
eye = (–9.43732, –6.77938, –3.0051),
And again, as before, we replace the rest of the camera data, set the proper
resolution, add the animation to the MODEL section and render this special
SDL file to create the reflection map.
Notes and Limitations
Shadows do not show up on surfaces that get all of their color from a reflection
map. In order for a shadow to appear on a reflection-mapped surface, the
surface must have a non-zero diffuse value.
A reflection-mapped object does not reflect itself. For example, a teapot will
not reflect its spout, but it will reflect the rest of the scene. This is because we
have to remove the object which will reflect from the special SDL file we create.
To get proper reflections of an object with itself requires ray tracing. This
method provides a cheaper alternative to ray tracing.
494 | Chapter 9 Tutorials
The methods for creating reflection maps described in this tutorial are for a
static object in the “reflection maps for an object” case and for a static object
and eye in the “reflection maps for planar surfaces” case. Should you wish to
create high quality reflections for a moving object in an animation, then a
new reflection map will have to be created for each frame of the animation.
In the case of planar objects, some time can be saved by noting that some of
the reflection map views do not “see” anything and are therefore black. These
views only need to be created once for the entire animation.
Creating projectile movement
Cross Reference
“An Introduction to Dynamics,” a companion tutorial, is strongly
recommended.
General Principles
Projectiles are objects which have an initial velocity and then move in a way
which depends on the forces acting on them.
The total force f acting on a mass m creates an acceleration a according to the
following equation:
f = ma
In a time step,
, the new velocity
can be derived from the old velocity
using:
Creating projectile movement | 495
where
is the instantaneous acceleration. The new position is given by:
These formulae assume that
is very small.
Projectiles have an initial velocity
and an initial position
. The force acting on the particle is computed taking into account gravity and
atmospheric drag, and the motion path for the projectile results. The equations
above work for each coordinate independently.
Terrestrial Cannon Ball
For a terrestrial cannon ball the effects of gravity are uniform. The force of
gravity acts down along the y axis and is proportional to the mass.
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This is Galileo's famous discovery that, in the absence of an atmosphere, all
objects fall with the same acceleration. (A cannon ball and a feather hit the
ground at the same time if released from the same height on the moon!).
The SDL file CourseWare/SDL/proj simulates a projectile moving through a
vacuum. The initial velocities along x and y are computed from a total velocity
and an angle of elevation. Try changing the angle to see which angle gives
the maximum range for the projectile. Range is defined as the distance it
moves through before returning to its initial y value.
Real projectiles, however, move through air. This slows them along their path
by creating a frictional force which acts in the opposite direction to the velocity
of the projectile (relative to the wind).
Therefore,
The SDL file CourseWare/SDL/dproj simulates this effect. Try different values
of “drag.” Is the optimal elevation angle still 45°?
The effect of the atmospheric drag is to reduce the horizontal velocity
eventually to zero, and to slow the ball both in its rise and descent. The ball
ultimately ends up descending vertically at a "terminal" velocity. The force of
gravity is then equal to the atmospheric drag.
(This is why parachutes are a good idea. The drag is greatly increased so that
terminal velocity decreases to the point that parachutists can land safely).
Most cannons, of course, do not float in free space, but sit on the ground.
Cannon balls, in the same way, collide with obstacles and bounce. A simple
floor may be implemented as follows.
Creating projectile movement | 497
The velocity normal to the surface after the collision is reversed in sign and
multiplied by the reflection coefficient called nelasticity. The actual new
position is given by:
The tangential new velocity is given by:
The intersection x coordinate is given by:
The next x coordinate for the particle is:
This model is implemented in the SDL file CourseWare/SDL/cproj. Try
changing the different values of the elasticities.
498 | Chapter 9 Tutorials
Roman Candle
While individual projectiles are useful in some circumstances, the true power
of procedural animation is revealed when a large number of objects are
involved. Consider a roman candle with a spray of sparks issuing from it. Each
particle will follow a trajectory that depends on its initial velocity and position.
The current velocity and position of each particle have to be stored in SDL
variables. This is made easy by defining arrays with an index that refers to the
particle number.
The SDL file CourseWare/SDL/roman illustrates how to create a firework of
exactly this sort. A looping "for" structure is used to process each particle in
turn. The variable "numpart" controls the number of particles in the animation
sequence; 10000 is plenty but they take a long time to animate and will not
play back in real time using preview. A "numpart" of 300 should prove adequate
for motion tests. The individual particles are modeled as cylinders which
extend from the previous position to the current one. The rendering is additive,
i.e. the cylinders are completely transparent with a colored incandescence
value. It happens that when large numbers of such particles are rendered on
top of each other, the color clips to white. This works rather nicely for the
firework.
Unfortunately, the "wireframe" rendering mode uses the color value for the
particles. The color value of these particles is actually black. This will lead to
black particles on a black background. For wireframe tests, it is necessary to
make the color white.
The wind velocity is a global control over the animation. Every particle is
affected along its trajectory. The SDL file CourseWare/SDL/roman uses an
animate statement to control the wind as a function of time. The wind blows
to the right strongly early in the animation and then gusts less later on. Try
experimenting with the drag coefficient, the particle velocities and the amount
of gravity. Try moving the spark origin point as a function of the birth time
to simulate a rocket.
Snow Storm
A snow storm may be thought of as a collection of particles. They are created
in a condensation or cloud layer. The flakes will have randomly distributed
positions and will then fall under gravity. Some flakes will have different drag
coefficients and so will fall at different rates. They will also tumble randomly
as they fall.
This model is implemented in the SDL file CourseWare/SDL/snow. When
rendered, the snow flakes, which are faces, are transparency mapped with
Creating projectile movement | 499
images which were derived from photographs of real snow flakes. The wind
direction is chosen to be perpendicular to the direction of view. This prevented
any snow flakes from blowing too close to the camera and so looking
enormous. A useful trick was also employed to prevent the system from
running out of snow flakes. The viewing frustum was considered to be looking
through an active volume of snow fall. The left and right sides of the volume
were outside of the field of view. This volume was defined by xrang and zrang. Any snow flakes which passed out of the positive x wall were moved
to the corresponding spot on the negative x wall. In this way the number of
snow flakes was used to best effect.
Programming Movement with Constraints
Piston Rod Example
Inverse kinematics is a technique for generating the joint angles for a hierarchy
in a way that fulfills geometrical constraints. A constraint is something which
reduces the freedom of movement of an object. For instance, a cylinder in a
cylinder block is constrained to one degree of freedom, i.e. sliding along its
length.
If a piston rod is to pivot both on a wheel and a cylinder, and the cylinder is
to be constrained linearly, then the system only has one degree of freedom.
The rotation angle
at A determines the angle at B which in turn determines the position of C.
A simple two-dimensional hierarchy has two degrees of freedom. It is the
constraint of the cylinder which makes the angle at B dependent on
and reduces the degrees of freedom to 1. Computing such dependencies is the
focus of inverse kinematics. This requires inverse trigonometric functions and
Pythagoras' Theorem.
500 | Chapter 9 Tutorials
Piston, Rod and Wheel l2 = p2 - (rSin
)2
where
(Pythagoras' Theorem)
Programming Movement with Constraints | 501
A Robot Arm
Robot arms are hierarchical devices for gripping and moving objects. The
position of the hand or "end effector" is controlled using the joint angles at
the shoulder and elbow. Consider a two-dimensional robot:
A Two-dimensional Robot
A two-dimensional robot arm is illustrated above. It has two degrees of freedom.
The variable alpha1 is the shoulder angle, while alpha2 is the elbow angle. If
both are equal to zero the arm points straight up in the air. The end coordinate
can be computed from the x1, alpha2 angles and the lengths l1, l2.
1
2
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This is forward kinematics and can either be used directly in SDL or the
hierarchy with joint angles alpha1, alpha2 will do it implicitly. Unfortunately
with robots it is usually required to specify the end and origin points explicitly
and derive the joint angles from them. This requires inverting equations 1
and 2. Rather than do this directly, it is easier to do this a piece at a time.
Consider the triangle OCE
By Pythagoras
By the Cosine rule
Hence C, hence alpha2.
Computing alpha2 is more difficult
Programming Movement with Constraints | 503
Take
to be horizontal and
to be at angle
.
The new end point is given by
The function atan2 can be used to get
.
This returns dif to y = 0.
The elevation above the horizontal can be obtained using
Therefore, alpha1 is given by
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A model can be made a little more complicated by the fact that the end points
have a z coordinate as well. However, a three-dimensional case can be reduced
to a two-dimensional case by constraining the arm to only lie in a vertical
plane.
First, the arm is rotated about the y axis by
(phi) where
then the two-dimensional equations are solved as before.
The arm so far described stops at the wrist. A real robot has a gripper which
can rotate on a ball joint about the wrist.
This may be achieved again using atan2 functions. The robot arm in this
example has a target point called (xtarget, ytarget, ztarget). The wrist is
positioned at a point defined by the approach vector (xtarget + xapproach,
ytarget + yapproach, ztarget + zapproach). The "gripper", which in fact is just
a cylinder, always points towards the target.
Try moving the target point outside the reach of the robot. What happens?
Try changing the lengths of the segments.
An Introduction to Dynamics
General Approach: Mass Spring Systems
Dynamics, in its common usage, just means change. In computer graphics it
has a specialized meaning which refers to the way that objects with mass
behave when subjected to forces.
A point mass m when subjected to a force, ƒ, will experience an acceleration,
a, in accordance with the following equation:
A point mass originally at rest will have an increase in velocity, v, defined by:
An Introduction to Dynamics | 505
where
means increment in time and
means change in velocity.
At the same time the velocity will cause a change in position:
Therefore, it is possible to find the new position based on the previous position
for each step. Thinking of the variables at increment i and increment i + 1:
The force ƒ was shown as ƒ(x) which means that the force is a function of
position, e.g.:
This means that a mass at positive x will experience a force pulling it towards
the origin. If the mass is at negative x the mass will also be pulled towards the
origin. A mass released at position x = p will oscillate around the origin. The
force simulates the effect of a spring. The value of k determines how stiff the
spring is. The larger the value of k, the stiffer the spring and the faster the
oscillation. Experiment usinge a wireframe to create preview files. Try different
values of k. The frequency will change. Try different values of mass. What
effects does this have?
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Damping
A mass on a perfect spring will oscillate forever. In practice, though, real world
devices experience friction and atmospheric drag. This may be simulated by
modifying the force acting on the mass, making it a function of the object’s
velocity as well as position:
where k is the spring constant and d is the damping. The larger the damping
value, the more the mass is slowed along its path. Too little damping and the
mass oscillates around the origin. Intermediate “critical” damping means that
the system comes to rest in the shortest time. Too much damping means that
the system gradually comes to rest.
Try a damping value of -0.5. The system gradually gains energy going faster
and faster. Negative damping corresponds to unstable systems. Such things
do occur in real life; for instance, a bridge in certain wind conditions may
oscillate until it fails. There is another source of instability which is due to
the way we are computing motion. The use of discrete time steps is only an
approximation. The smaller the time step the more accurate the solution. The
mass overshoots where it should be and experiences a greater restoring force
than it should. It then overshoots the other way. Oscillations build up and,
for more complex objects, the system shakes itself to pieces. This problem
may be overcome in two ways. The first is to decrease the time step: this may
be achieved by having many subintervals per frame of animation.
This enhances the accuracy of the animation and is vital for fast moving
effects. Unfortunately, the more subintervals used, the more expensive the
solution, and this can be prohibitive if large numbers of objects are involved.
The instability may be counteracted by increasing the damping in the system.
Too much damping will lead to altered behaviour; too little and the system
becomes unstable and “blows up.”
Extending to More Dimensions — Animating a Chain
The previous spring example was only in one dimension. Most problems of
interest work in two or three dimensions.
A force that varies as a function of the distance between two point masses
may be expressed as follows:
An Introduction to Dynamics | 507
where
and
and
are vectors, and r is the distance between the point masses. n should be set to
-1 for a spring, and 2 for gravity.
This may be expressed in terms of components as follows:
for points (x1, y1, z1,) and (x2, y2, z2),
The force along x, y, z acting on particle 1 will be:
A damping term should be proportional to relative motion along the line
joining the two masses. This may be achieved by computing the dot product
of the difference in position with the difference in velocity:
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It is possible to have collections of point masses. The position and velocity of
each particle is stored in arrays. For each iteration, the cumulative force is
computed for each mass pair of interactions.
Cloth and Drapery
Cloth or drapery may be simulated using a two dimensional mesh of point
masses. These are animated using dynamics and then used to define the control
points of a patch. The masses may be considered to be a rectangular mesh in
u, v space.
The above illustrates the arrangement of the springs for cloth. Springs run
horizontally and vertically to simulate the direct thread properties. Diagonal
springs prevent the cloth from shearing.
The constraints holding the top two corners of the cloth move closer together
as the animation progresses. Try using larger values of "dbond", the variables
which control the shear coefficient. Very large values, such as 1.0 will give a
material which behaves more like paper than cloth.
If you intend to render the cloth image, rather than using the wireframe, you
should note two things. First, the "divisions" in the patch statement should
be increased to three or four. Second, the variable "startframe" should be set
to the value of the first frame to be rendered. This is useful if you want to
examine just one frame or if you want to restart a render half way through
the animation.
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Three Dimensional Systems: Jelly and Snakes
Two dimensional sheets are useful for drapery and flags, but often real objects
are three dimensional solids. These may be simulated using three dimensional
lattices of masses.
A Cubic Mass - Spring System
A three dimensional lattice will deform when it collides with constraints. It
will wobble like a piece of jelly, but it is essentially passive.
A more interesting effect is achievable if the spring tensions are animated with
time. This can be used to simulate muscle contractions in biological forms
such as worms and snakes. The edge spring lengths are animated sinusoidally
to produce sinuous motion in the snake. The directional friction due to the
scales is implemented by not permitting the snake to slide backwards. This,
and the muscle contractions, cause the snake to slither along. The variable
"numxp" controls the number of segments in the snake. A "numxp" of 5
produces a wriggling grub-like motion but is quite fast. A "numxp" of 30 gives
a truly convincing snake and takes considerably more time.
As an exercise, try applying a lifting force to one end of the snake and see the
resulting movement.
Creating Fiery Smoke
Overview
This tutorial discusses how to use a series of concentric ellipsoids with
transparency solid textures to fake the appearance of a column of smoke. The
use of solid texture transformations allows the smoke to be animated as a
function of time.
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Cross References
We suggest that you read the section on the sCloud on page 459 procedure in
Part 3 of this manual.
Creating Smoke
Ellipsoidal Geometry
A series of nested ellipsoids can be used to simulate fiery smoke. Each ellipsoid
is given a transparency map defined by sCloud. This procedure creates a fractal
with a slope dependent offset added to it. This leads to an opaque center and
a ragged transparent edge. Each ellipsoid looks like a puff of smoke. The fire
effect is achieved by making the ellipsoids have different optical properties.
The outer ellipsoid (surface 1) is made grey and dim. The inner ellipsoids are
made successively brighter and more orange.
The static appearance is convincing although not brilliant. However, when
the solid textures are animated the results are very good. Each surface
description is given a different solid texture transformation which allows the
smoke effects to move at different rates.
Try scaling all of the transformations using scales of 10 and 0.1. What effect
does this have on the appearance? How does the edge threshold affect the
extent of the smoke?
Animating a Sunrise
Purpose
This tutorial is intended to teach you how to do a sunrise over rippling water.
In particular, we look at ways to deal with the problem of the large change in
brightness as the sun rises.
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Other Applications
Environment maps can be used as backgrounds and for reflections with
spherical, cubic and chrome maps.
Cross Reference
You should be familiar with the explanation of the "Sky" procedure in Part 3
of this manual, and in the Shader section of Rendering in AliasStudio. It
describes the various parameters which control the simulation of a planetary
atmosphere. As well, the explanations of water waves and ripples and Water
in the Natural Phenomena section discuss the principles used to create water
and detail the parameters for Water.
The Scene
The water in this scene consists of a single flat patch with waves on the surface
of the patch created using a bump map of the Water procedure. This patch
stretches from -200 to 200 units along the x and z axes. This ensures that,
when viewed from the eye point, the water plane stretches to the horizon.
The background is a direct view of the procedural environment "Sky". This is
also used as a reflection map on the patch to show the sky reflected in the
water.
The Animation
There are several primary processes in the animation. The first is the movement
of the water waves across the patch. The second is the movement of the sun
as it rises above the horizon. The third is the translation of the clouds across
the sky. The clouds also become thinner as the day progresses. A secondary
process in the animation is the use of the brightness variables to compensate
for the enormous changes of brightness which occur during a sunrise.
Each of these processes is now discussed in some detail.
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Animating the Water
Since relative displacement maps affect the underlying geometry, to get a
realistic level of detail a very high level of subdivision would have to be used;
to get around this, a bump map was used instead, and an "amult" value of
0.01 was chosen. The choice of small amplitude waves avoided the expense
of using a displacement map instead of a bump map. The large extent of the
water patch would have required "urepeat" and "vrepeat" to be 300 for the
individual nearby waves to look a reasonable size. This, in turn, would have
led to the need for udivisions and vdivisions for the patch of about 1000. This
would generate so many triangles that the renderer would run out of memory.
A bump map, on the other hand, affects the normal at the point of intersection
and leaves the geometry unchanged, so the entire area can be characterized
using the minimal two triangles (udivisions and vdivisions of 1).
The "wave_frequency_step" of 0.125 was chosen so as to have several waveforms
of almost the same frequency superimposed on top of each other. Large values
lead to repetitive, unattractive waves.
The "wave_time" is made of a function of the frame number "frame". In this
way the waves move smoothly from frame to frame. The "blurmult" and
"bluroffset" values mean that the water is sampled in a very small area to
compute the slope. This prevents the water from looking flat near the horizon.
The only correct way to antialias bump maps is to supersample them
everywhere. Blurring the bump map texture merely blurs out the detail. An
"aathreshold" of zero ensures supersampling for every pixel. The "aalevel" of
2 was chosen since it reduced aliasing artifacts without making the rendering
time completely prohibitive.
Animating the Sun
The sun position is defined in terms of azimuth and elevation angles with
respect to the earth. Since the real world rotates, the sun moves across the
sky. The correct astronomical animation would be to rotate these angles at a
uniform speed. However, for this animation we want the sun to rise quickly
at the beginning, and gradually come to a stop. This was achieved by using
an ease function.
The field of view for this animation was chosen to be 90°. This has the
advantage that large color changes take place over an angle of 90° for a more
striking image. However, the large fov has several disadvantages. First, if the
sun were to have its real diameter of 1/2 degree, it would be tiny on the screen.
Secondly, a sphere near the edge of a perspective image projects onto the
screen as an ellipse, not a circle. This effect gets worse as the field of view
increases.
Animating a Sunrise | 513
Unfortunately an elliptical sun looks wrong. Fortunately there is an optical
effect in the real world's atmosphere which bulges the sun horizontally for
low elevations. Thus an "aspect" ratio was chosen which made the sun circular
when high in the sky and squashed when low in the sky. If other pieces of
geometry are rendered at the same time, they may be laterally distorted, but
for this animation it worked.
The sun radius value is changed to compensate for the elongation. It is also
much larger than the real sun would appear.
Animating the Clouds
The clouds in the sky were created by using the 8 bit pix file FractalBW. This
is a fractal texture which wraps at its edges and creates realistic looking clouds.
Any pix file could be used. The clouds could be a scanned-in logo or an
animated matte sequence if desired. The clouds for this piece were animated
in two ways. First, they were translated across the sky by moving the
"cloud_xoffset" and "cloud_yoffset" linearly with the frame number. Also, to
simulate the thinning of the clouds as the sky warmed up, the cloud_threshold
was changed exponentially as a function of the frame time.
Compensating for Brightness Changes
A problem with accurate simulations of sunrises and sunsets is that the
brightness of the sky changes by several orders of magnitude. As the sun comes
up it gets brighter. In real photography an exposure long enough to catch the
subtle beauty of dawn would be whited out by a mid morning sky. In the
same way, the computer graphics medium only handles about one order of
magnitude of contrast. We need to compensate for this by using a
multiplicative "brightness" factor.
The illustration above shows that for large radius planets the distance through
the atmosphere for a ray at angle A is approximately:
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A, in this example, is equivalent to the sun's elevation. The brightness decays
exponentially with the distance through the atmosphere. However, for this
example, the brightness was made proportional to 1/(l + c) where c prevented
the brightness becoming infinite for l = 0. This compensation works fairly
well, although the sun does flare up slightly half way through the animation.
You can try more sophisticated compensation, although we suggest that you
investigate these effects using non-antialiased very low resolution images.
A Caveat About Rendering Times
Both "Water" and "Sky" are very expensive procedures. The water model which
covers half the screen, is time consuming because it is a time dependent
procedure which treats each frequency separately. This time is proportional
to the area of the water in screen space. For an NTSC image with an
anti-aliasing level (aalevel) of 2 and an anti-aliasing threshold (aathreshold)
of zero, the water procedure adds twenty minutes to the rendering time on
an SGI 4D workstation.
The sky procedure is also extremely costly. It involves a double integral through
the atmosphere. For the same NTSC image, as above, having the sky both as
a reflection map on the water and as a background, adds forty minutes to the
rendering time on an SGI 4D workstation.
At an hour per frame you may ask why bother? The answers are two-fold.
First, the results are rather beautiful and second, the sky procedure will be
better understood. One particular time of day (sun elevation) may be rendered
once into a cubic environment map and then used for backgrounds and
reflections for an entire animation sequence. That is not done here because
we change the sky parameters as a function of time.
Creating a Tree
Overview
This tutorial describes the use of "for" loops and nested transformations to
create a fir tree. The model developed here uses differential equations to
simulate the growth of branches. This allows the animation of a tree growing
from sapling to adult.
Branching and Looping
A tree may be described as a trunk with branches. On each branch are other
branches, etc.
Creating a Tree | 515
The loop for each branch is as follows:
{
Create a branch
loop for each sub-branch
{
create a sub-branch
loop for each pine needle
{
create a sub-sub-branch
}
}
}
Almost any tree model will have such a structure. The trick is to know how
to position the sub-branches on each branch and how many to create. The
positioning is comparatively simple if the branching structure is also used to
control the transformation hierarchy: then the branches only need to be
rotated about their origin and then translated along the branch.
Dynamic Model of Simple Tree Growth
Along a particular limb the growth rate is zero below a certain time and jumps
to max at a time proportional to the index position along the branch. The
growth rate decays to zero exponentially thereafter.
For position i
where M is the maximum length for the segment,
t is the time,
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k is the growth initiation rate, and
d is the growth rate.
The position of the segment a is L(a) which is given by
Given an index value
Creating a Tree | 517
Where m defines the maximum rate of change of position with respect to the
branch number,
d defines the time interval over which growth rate decays to zero, and
k defines the rate at which the new growth initiator moves with respect to
position index.
Rendering Tips
The tree generated by this file looks very convincing with a stretched fractal
bump map for bark. Unfortunately, the fine pointed elements of the branches
lead to sampling problems unless the "aathreshold" is set to zero. This, in turn,
leads to increased rendering times.
The needle density was increased until the computer ran out of paging disk.
Fir trees are pathologically complicated. Try using fewer branches and no
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needles. Try placing fruit on the branches, or create candles for a Christmas
tree. Try adapting the model for curved branches, such as on an apple tree.
Creating Rendered Stereo Pairs
To create stereo, run-length-encoded images for display on the Stereographics
monitor, several changes must be made to an ordinary SDL file.
DEFINITION Section Changes for stereo pairs
First, a flag must be set in the DEFINITION section to have the renderer create
a stereo pair. The syntax for it is:
stereo = <scalar>;
where the value of the scalar is 0 (FALSE) or not 0 (TRUE).
The setting of these variables can be performed in the interactive package
through the camera editor.
The stereo flag specifies if the camera(s) is to render a stereo pair of images. If
this component is TRUE, the pix and mask components (if specified) will have
two file names generated for the left and right images.
The generated names will be,
"<specified_name>_left"
"<specified_name>_right"
The “left” and “right” correspond to the output pix files for the left and right
eyes. The filename may be animated like other animated filenames (i.e.,
“basename”extension_expression). If the extension expression is missing and
the rendering is an animation, the name will have a standard frame extension.
Any extension is appended after the suffixes "_left" and "_right".
For example, if the SDL contained camera (pix="pix/abc",... and it were
animated, the renderer would create two pix files for the first frame,
"pix/abc_left.1" and "pix/abc_right.1"
One other variable must be set:
stereo_eye_offset = <scalar>;
The offset specifies the eye separation between the eye points of two cameras
that will be used to render the stereo pair. The offset is in world coordinates
Creating Rendered Stereo Pairs | 519
and specifies the eye’s off-set in X. This variable can also be set in the camera
editor in the interactive package.
Example:
stereo_eye_offset = 0.55;
The parameter stereo_eye_offset specifies the spacing between the eyes in
modeling space. A single value, it controls the amount of disparity between
the two eyes by offsetting the eye point for each image by the amount
specified. The value of stereo_eye_offset can be computed to a first
approximation as follows:
If D is the distance in inches that the person sits from the screen, e.g., 19
inches, and E is half the distance between the left and right eye (e.g., E = 1.5
inches), then
Note the camera view position in the interactive package. It is used to
determine the zero parallax depth for the scene. The view position is the point
at which the left and right images will be coincident on the screen. It should
be chosen close to the centre of attention.
In addition to the "stereo" switch and the "stereo_eye_offset", other changes
must also be made.
Set the resolution for stereo images to 1280 by 480, if you are using the
Stereographics monitor.
Good quality is necessary for stereo images. Ensure that the aalevel (both min
and max) and aathreshold values are set appropriately.
The viewport for stereographic viewing should always be 0 1279 0 479. For
the aspect, use 1280/1024 (the value will be computed).
The fov should be adjusted to the viewing distance between the user and the
stereographic screen. In the attached example, set for a viewing distance of
19 inches, the fov = 2.0*atand(4.5/19.0).
If any lights of type ambient are used, ensure that the ambient_shade value
is set to 0 (it defaults to 0.5) for each. If it is set to a value other than 0, the
lighting will be different for each eye.
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Render this SDL file once to create the pix files for both eyes.
Showing Stereo Images:
To view these files on the Stereographics monitor, use the stand alone program
showstereo. If the pix files are not full screen resolution (1280 by 480), they
will be resized to the correct resolution automatically, by pixel replication if
they are too small, or by truncation if too large. If the image is too large, as
much of the image as can fit on the screen will be shown, from the upper left
corner.
Alternatively, you can use the standalone utility rb_stereo to create a red-blue
stereo image that can be viewed on the monitor with readily-available red-blue
“stereo” glasses.
Helpful Hints for Stereo Image Modeling
When creating images for stereo pairs, some effects work better than others.
Keep the following in mind when creating your model:
1 Models that fit completely in the image window appear more
three-dimensional than models that are cut off by the edges of the screen.
2 Thin, plain verticals are very difficult to merge into a single object when
viewing, as there isn’t much information for the eye to use to combine
them. Generally speaking, an object with a fair amount of detail (color
and light variations, texture, irregularity in shape) provides more
information than a plain object.
3 Very high contrast of lights and darks in the image results in ghost images.
4 The closer the viewpoint is to the back of the scene, the more the scene
will project from the Stereographics display: the closer to the front, the
more the scene will recede into the monitor. Remember that having
objects too “close” to, or too “far” from the viewer’s eyes results in
discomfort as the viewer crosses or uncrosses his or her eyes to merge the
two images.
A useful example file is found in CourseWare/SDL/stereo.
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522
Index
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