Backgrounds, Inheritance in
GameMaker (BrickMania 1 of 2)
Foundations of Interactive Game Design
Professor Jim Whitehead
January 28, 2008
Creative Commons
Attribution 3.0
creativecommons.org/licenses/by/3.0
Upcoming Assignments
• Wednesday: Game Concept Document
► A compelling document that sells your game concept
► Title page
• Title of game, name of group, name of team members, sample artwork
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Overview page
• Table at top: game genre, platform (PC/GameMaker, PC/RPG Maker, etc.), team size
• Key points section
– Bulleted list of important elements of gameplay
– Goal of game, what makes game unique, main characters, main fictional
elements
– Sample artwork image to give feel of the game
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Biographies
• True, pocket biographies of each team member (1-2 paragraphs each) stressing experience
that makes you a strong game designer
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1-3 pages giving a textual description of the game
• Fictional background, brief description of characters, goal of player in game, how does
player interact with the game, brief description of levels, game audience, other important
elements as needed.
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1-2 pages of sample conceptual artwork
• Hand-drawn sketches are fine
•
Start early!
Let’s create a simple Breakout game
• Game elements
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Background
Ball
Paddle
Score
Lives
3 brick types
Playfield is
smaller than
screen
Backgrounds
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Background
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Represents a static background image
Defined separately, then combined with a room
Can move, or be motionless
Many uses
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Moving starfield
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Create starfield bitmap image
Define as background
Have it move backwards: creates sensation of motion
Image surrounding playfield of game
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BreakMania uses a background this way
Detecting edges of background
• Reduce boundary objects
► In
tile-based games, need many tiles to create an
interesting level
► With objects, would need separate object for each tile
type
• Can slow a game down
► Instead,
create background image
► Then, use single, invisible boundary object for collision
detection
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Can be easier to create background in drawing
program
► Then,
just use simple shapes for collision detection
► May be easier than converting to tiles at times
Creating a Background
• Resources -> Create Background
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Enter name
Can have a
transparent color
• Useful for multidepth scrolling
background
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Load background
image
• Select file
Break Mania Background
• Created using
The GIMP
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Free software
PC & Mac
Used fills &
text effects
that come
with GIMP
score box
playfield
Create Room
• Resources -> Create Room
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Click on “Settings Tab” … enter name of Room
Add Background to Room
• Unselect “Draw background color”
• Select
“Visible when
room starts”
• Use pull-down
menu to
select
background
image
Note grid alignment
with background
image boundaries –
need to plan ahead
for this!
Select grid size to match size of
sprites – for us, 10x10 works well
Create Sprites
• For BreakMania need sprites for:
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Paddle
Ball
Three brick types
Small paddle (for lives display)
Three different wall types
• Two different vertical (10x50,10x30), & one horizontal (10x50)
• Used to create invisible barrier for edge of playfield
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Game over text
Create Objects
• For most of the sprites, need to create an associated
object
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Resources -> Create Object
Solid: Paddle, three brick objects, three wall objects
Not solid: Ball, game over
No need to
create small
paddle object
Only need to use
the sprite for lives
display
• For now,
no behavior
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Will add soon
Create Invisible Objects
• Three wall types all must be invisible
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Will place them over the background
Ball will collide with invisible wall objects
To player, will seem like collision with background
Wall objects
placed at edge of
black playfield.
Show with dotted
lines to represent
being invisible
during gameplay
Making Objects Invisible
• Click on “visible” toggle
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If no check, is invisible
Make solid for bounce behavior
Place Objects in Room
• Click on game room, then objects tab
• Use pulldown menu to select object to place
• Invisible
walls
• Bricks
• Paddle
• Ball
Ball Behavior
• When ball is created, want it to start moving
upwards at an angle
• Use create event on ball
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Start moving in direction
Click two up diagonal arrows
Speed of 10
Paddle Behavior - Movement
• Left arrow moves left, right arrow moves right
• Up/down arrows stop
• Use keypress events for these
Paddle Behavior – Ball Collision
• Ball should bounce after hitting paddle
Drag-n-drop bounce to actions
Pick collision event,
then select ball from
pull-down menu that
appears
Wall Behavior
• If paddle collides with wall, paddle stops
• If ball collides with wall, want it to bounce
• Could define this separately on all three wall types
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Tedious
Error-prone, since every change needs to be copied
over to the other two walls
Would be nice if this could be stated once, for all walls
• Use object inheritance
Inheritance
• Objects can have a parent
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All of the behaviors of the parent are copied to its
children
Imagine a “wall-mother” object
• A collision event with the ball causes the ball to bounce
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Now, make all three invisible walls have wall-mother as
a parent
• All invisible walls now collide with the ball like the mother!
• By defining one wall-mother object, avoids cut-and-paste of
collision behavior to three invisible walls.
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Note that it is possible to change inherited behavior on
children
• Just define the specific event a different way. Child’s definition
always trumps that of the parent.
Creating Wall-Mother
Make ball bounce off walls
No sprite, since
we’re using this
just for behavior.
Leave it to
children to
specify exact
visual shape.
Don’t set
visible, do set
solid, since
that’s what
children should
be. Visible
doesn’t matter
for wall-mother,
since it has no
sprite
Now, set parent of invisible walls
Note no events or actions. It gets these
all from its parent, wall-mother!
Set parent to wallmother using pulldown menu here
Brick behavior
• If a ball hits a brick:
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It should disappear
Small ring effect
Play sound
Ball should bounce
Score should go up
• Three brick types
• Use inheritance
from new
brick-mother
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Put collision
behavior on mother
Reuse on all bricks
• Set each colored brick’s
parent to “brick-mother”
Ball Bouncing Off Brick
• The collision of brick with ball is on brick-mother
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But, we want the ball to bounce, not the brick
How to do this?
Each collision is between
two objects:
• The object hosting the collision event
• The “other” object
• In this case, the brick is hosting the
collision, the ball is the “other”
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To indicate ball should bounce,
select “other” in bounce
dialog box
Making Brick Disappear
• Each brick on screen is an instance of a brick object
• Can think of the object as a kind of “mold” that can stamp
out many different instances of the object
• Brick object: mold :: individual bricks: instances
• To make
brick disappear:
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Destroy
the instance
On tab
main1
Creating Brick Ring Effect
• On draw tab, select “Create Effect” button
Add offset so ring emerges
from center of the brick
Click relative so ring
emerges from brick, not
upper left corner of screen!