Radiance Cache Splatting:
A GPU-Friendly Global
Illumination Algorithm
P. Gautron J. Křivánek
K. Bouatouch S. Pattanaik
Global Illumination
Why?
Direct
Indirect
Global Illumination
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Global Illumination
How?
∫
Lo(P, ωo) = Li(P, ωi) * BRDF(ωo, ωi) *cos(θ)dωi
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Global Illumination
How?
∫
Lo(P, ωo) = Li(P, ωi) * BRDF(ωo, ωi) *cos(θ)dωi
No analytical solution
Numerical methods
- Radiosity
- Photon mapping
- Path tracing
- Bidirectional path tracing
- Irradiance & Radiance caching
-…
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GPUs
Speed
GPU
Speed
Time
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GPUs
Versatility
Linear algebra
Fluid dynamics
Signal processing
Databases
…
Simple 3D
graphics only
And graphics!
Time
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Global Illumination & GPUs
CPU
GPU
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Global Illumination & GPUs
Previous work
Hemicube
Cohen et al. 1985
Photon mapping on GPU
Purcell et al. 2003
PRT
Sloan et al. 2002
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Contributions
A reformulation of (Ir)Radiance caching …
- No complex data structure
- Fast, image-space (ir)radiance interpolation
- Fast approximation of hemisphere sampling
… for fast and easy GPU implementation
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Outline
Introduction
Irradiance & Radiance Caching
Our method: Radiance Cache Splatting
Results
Conclusion & Future Work
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Outline
Introduction
Irradiance & Radiance Caching
Our method: Radiance Cache Splatting
Results
Conclusion & Future Work
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Irradiance Caching
Sparse computation of indirect diffuse lighting


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Irradiance Caching
Sparse computation of indirect diffuse lighting
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Irradiance Caching
Sparse computation of indirect diffuse lighting
Interpolation

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Interpolation
n
nk
E
E(P) = Ek+ (nk x n)
r
Ek+ D
t
Ek
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Interpolation
n2
n n3 n4
n1
E
E(P) =
Σ
k S
Ek+ (nk x n)
r
Ek+ D
t
Ek
wk(P)
Σ
wk(P)
k S
S = { k / wk(P) > 1/a }
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Radiance Caching
Extension of irradiance caching to glossy interreflections
Cache directional distribution of light
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Radiance Caching
Extension of irradiance caching to glossy interreflections
Cache directional distribution of light
Hemispherical Harmonics
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Radiance Caching
HSH
Incident Radiance

HSH
BRDF
L1
L2
f1
f2
Ln
fn
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Implementation
Cache Record Computation
Ray tracing


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Implementation
Cache storage
4
6
1
10
8
2
11
3
3
13
2
4
5
6
7
12
8
9
5
1
9
10
11
12
13
7
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Outline
Introduction
Irradiance & Radiance Caching
Our method: Radiance Cache Splatting
Results
Conclusion & Future Work
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(Ir)Radiance Caching vs GPU
(Ir)Radiance
Caching
GPU
Ray tracing
Rasterization
Cache stored in tree
Spatial queries
?
1/2/3D textures
Texture lookups
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Reformulation
(Ir)Radiance
Caching
Octree
Ray tracing
Our
method
(Ir)Radiance
Caching
Native GPU
features
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Outline
Introduction
Irradiance & Radiance Caching
Our method: Radiance Cache Splatting
From octree to splatting
From ray tracing to rasterization
Overall algorithm
Results
Conclusion & Future Work
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Outline
Introduction
Irradiance & Radiance Caching
Our method: Radiance Cache Splatting
From octree to splatting
From ray tracing to rasterization
Overall algorithm
Results
Conclusion & Future Work
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From Octree to Splatting
n2
n n3 n4
Irradiance Interpolation
n1
E
E(P) =
Σ
k S
Ek+ (nk x n)
r
Ek+ D
t
Ek
wk(P)
Σ
wk(P)
k S
S = { k / wk(P) > 1/a }
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From Octree to Splatting
Irradiance Caching Weighting Function
n
nk
Pk
P
1
wk(P) =
Distance
||P-Pk||
+
Rk
1-n.nk
Normals divergence
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From Octree to Splatting
Simplified Weighting Function
nk
n
Pk P
1
wk(P) =
Distance
||P-Pk||
+
Rk
1-n.nk
Normals divergence
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From Octree to Splatting
Simplified Weighting Function
nk
n
Pk P
~
w (P) =
k
Distance
Distance
1
1
||P-P
||P-Pkk||||
+
R
Rkk
1-n.nk
Normals divergence
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From Octree to Splatting
Simplified Weighting Function
n
nk
Pk
P
aRk
~
w (P) =
k
Rk
||P-Pk||
> 1/a
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From Octree to Splatting
Principle
~
w (P) =
k
Rk
||P-Pk||
> 1/a
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From Octree to Splatting
Principle
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From Octree to Splatting
Principle
wk(P)>1/a ?
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From Octree to Splatting
Principle
wk(P)E(P)
wk(P)
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From Octree to Splatting
Principle
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From Octree to Splatting
Principle
Σw (P)E(P)
k
k
Σ w (P)
k
k
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From Octree to Splatting
Final Image Generation
Σw (P)E(P)
k
k
Σ w (P)
k
k
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From Octree to Splatting
Example
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Outline
Introduction
Irradiance & Radiance Caching
Our method: Radiance Cache Splatting
From octree to splatting
From ray tracing to rasterization
Overall algorithm
Results
Conclusion & Future Work
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From Ray Tracing to Rasterization
CPU

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From Ray Tracing to Rasterization
Simple plane sampling
GPU
Vertex Fragment
Shader Shader

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From Ray Tracing to Rasterization
Simple plane sampling
GPU
Vertex Fragment
Shader Shader

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From Ray Tracing to Rasterization
Simple plane sampling
GPU
Vertex Fragment
Shader Shader
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From Ray Tracing to Rasterization
Simple plane sampling
GPU
Vertex Fragment
Shader Shader
Incoming radiance loss
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From Ray Tracing to Rasterization
Our plane sampling
GPU
Vertex Fragment
Shader Shader

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From Ray Tracing to Rasterization
Our plane sampling
GPU
Vertex Fragment
Shader Shader
Compensation of incoming radiance loss
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Our plane sampling
Summary
3x more accurate than simple plane sampling
Plausible directional information
Easy implementation on GPU
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Outline
Introduction
Irradiance & Radiance Caching
Our method: Radiance Cache Splatting
From octree to splatting
From ray tracing to rasterization
Overall algorithm
Results
Conclusion & Future Work
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Algorithm
Step 1 : information generation
GPU
Vertex Fragment
Shader Shader
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Algorithm
Step 2 : detection
CPU
?
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Algorithm
Step 2 : detection
CPU
GPU
Hemisphere sampling
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Algorithm
Step 2 : detection
CPU
GPU
Hemisphere sampling
?
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Algorithm
Step 2 : detection
CPU
?
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Algorithm
Step 2 : detection
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CPU
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Algorithm
Step 3 : display
GPU
Vertex Fragment
Shader Shader
Matrices
Vertex
Shader
Record information
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Algorithm
Step 3 : display
GPU
Vertex Fragment
Shader Shader
Fragment
Shader
Record information
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Algorithm
Step 3 : display
GPU
Vertex Fragment
Shader Shader
Fragment
Shader
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Algorithm
Summary
No spatial data structure
Spatial queries replaced by splatting
Interpolation by blending
No quality loss compared to (Ir)Radiance Caching
No order constraint for image traversal
Can be implemented using native GPU features
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Our renderer
Record computation
1-bounce GI: shadow maps & plane sampling
Indirect lighting
Radiance cache splatting
Direct lighting
GPU per-pixel lighting & shadow maps
CPU ray tracing
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Outline
Introduction
Irradiance & Radiance Caching
Our method: Radiance Cache Splatting
Results
Conclusion & Future Work
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Results
Sibenik Cathedral (80K triangles)
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Results
Sponza Atrium (66K triangles)
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Results
Comparison with Radiance
Sibenik Cathedral
Sponza Atrium
Radiance
Time
425 s
645 s
Our
Renderer
Time
14,3 s
13,7 s
Speedup
29,7
47,1
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Results
From Irradiance to Radiance Caching: Venus (24K triangles)
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Conclusion
Reformulation of (Ir)Radiance Caching
Speedup: 29x – 47x
Interactive or fast, high quality rendering
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Future Work
Multiple bounces
Area light sources
All-Frequency BRDFs
More complex models
Better hemisphere sampling
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Any questions?
Radiance Cache Splatting on the web:
http://www.irisa.fr/siames/Pascal.Gautron/
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