Radiance Cache Splatting:A GPU-Friendly Global Illumination Algorithm

P. Gautron J. Křivánek

K. Bouatouch S. Pattanaik

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Global IlluminationWhy?

Direct Indirect

Global Illumination

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Global IlluminationHow?

Lo(P, ωo) ∫ Li(P, ωi)= * BRDF(ωo, ωi) *cos(θ)dωi

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Global IlluminationHow?

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

GPUSpeed

Time

Speed

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GPUsVersatility

Time

Linear algebraFluid dynamicsSignal processingDatabases…

And graphics!Simple 3D graphics only

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Global Illumination & GPUs

CPU

GPU

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Global Illumination & GPUsPrevious work

HemicubeCohen et al. 1985

PRTSloan et al. 2002

Photon mapping on GPUPurcell et al. 2003

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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 CachingSparse computation of indirect diffuse lighting

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Irradiance Caching

Interpolation

Sparse computation of indirect diffuse lighting

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Interpolation

=E(P)

nk

n

Ek+ (nk x n)rEk+ D

tEk

E

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Interpolation

=E(P)

wk(P)

Σk S

wk(P)

Σk S

Ek+ (nk x n)rEk+ D

tEk

E

S = { k / wk(P) > 1/a }

n1

nn2n3 n4

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Radiance CachingExtension of irradiance caching to glossy interreflections

Cache directional distribution of light

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Radiance CachingExtension of irradiance caching to glossy interreflections

Cache directional distribution of light

Hemispherical Harmonics

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Radiance Caching

HSHIncident Radiance

HSHBRDF

L1

L2

Ln

f1

f2

fn

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Implementation

Ray tracing

Cache Record Computation

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Implementation

1

1

2 3

2

3

4 5 6 7

4

5

6

7

8 9 10 11 12 13

8

9

10

11

12

13

Cache storage

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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 1/2/3D textures

Spatial queries Texture lookups

?

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Reformulation

Octree

Ray tracing

(Ir)Radiance Caching

Native GPUfeatures

(Ir)Radiance CachingOur

method

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Outline

Introduction

Irradiance & Radiance Caching

Our method: Radiance Cache Splatting

Results

Conclusion & Future Work

From octree to splattingFrom ray tracing to rasterizationOverall algorithm

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Outline

Introduction

Irradiance & Radiance Caching

Our method: Radiance Cache Splatting

Results

Conclusion & Future Work

From octree to splattingFrom ray tracing to rasterizationOverall algorithm

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From Octree to Splatting

=E(P)

wk(P)

Σk S

wk(P)

Σk S

Ek+ (nk x n)rEk+ D

tEk

E

S = { k / wk(P) > 1/a }

Irradiance Interpolation

n1

nn2n3 n4

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From Octree to SplattingIrradiance Caching Weighting Function

nk

n

PPk

wk(P) = 1

||P-Pk||

Rk

+ 1-n.nk

Distance Normals divergence

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From Octree to SplattingSimplified Weighting Function

wk(P) = 1

||P-Pk||

Rk

+ 1-n.nk

Distance Normals divergence

nk n

PPk

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From Octree to SplattingSimplified Weighting Function

wk(P) = 1

||P-Pk||

Rk

+ 1-n.nk

Distance Normals divergence

nk n

PPk

wk(P) = 1

||P-Pk||

Rk

Distance

~

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From Octree to SplattingSimplified Weighting Function

nkn

PPk

aRk

wk(P) = ||P-Pk||

Rk > 1/a ~

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From Octree to SplattingPrinciple

wk(P) = ||P-Pk||

Rk > 1/a ~

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From Octree to SplattingPrinciple

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From Octree to SplattingPrinciple

wk(P)>1/a ?

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From Octree to SplattingPrinciple

wk(P)E(P)

wk(P)

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From Octree to SplattingPrinciple

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From Octree to SplattingPrinciple

wk(P)E(P)

wk(P)

Σk

Σk

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From Octree to SplattingFinal Image Generation

wk(P)E(P)Σk

wk(P)Σk

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From Octree to SplattingExample

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Outline

Introduction

Irradiance & Radiance Caching

Our method: Radiance Cache Splatting

Results

Conclusion & Future Work

From octree to splattingFrom ray tracing to rasterizationOverall algorithm

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From Ray Tracing to RasterizationCPU

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From Ray Tracing to Rasterization

GPU

VertexShader

FragmentShader

Simple plane sampling

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From Ray Tracing to Rasterization

GPU

VertexShader

FragmentShader

Simple plane sampling

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From Ray Tracing to RasterizationGPU

VertexShader

FragmentShader

Simple plane sampling

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From Ray Tracing to RasterizationGPU

VertexShader

FragmentShader

Simple plane sampling

Incoming radiance loss

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From Ray Tracing to Rasterization

GPU

VertexShader

FragmentShader

Our plane sampling

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From Ray Tracing to RasterizationGPU

VertexShader

FragmentShader

Our plane sampling

Compensation of incoming radiance loss

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Our plane samplingSummary

Easy implementation on GPU

3x more accurate than simple plane sampling

Plausible directional information

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Outline

Introduction

Irradiance & Radiance Caching

Our method: Radiance Cache Splatting

Results

Conclusion & Future Work

From octree to splattingFrom ray tracing to rasterizationOverall algorithm

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AlgorithmStep 1 : information generation GPU

VertexShader

FragmentShader

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AlgorithmStep 2 : detection CPU

?

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AlgorithmStep 2 : detection CPU

GPUHemisphere sampling

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AlgorithmStep 2 : detection CPU

?

GPUHemisphere sampling

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AlgorithmStep 2 : detection CPU

?

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AlgorithmStep 2 : detection CPU

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AlgorithmStep 3 : display GPU

VertexShader

FragmentShader

VertexShader

Matrices

Record information

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AlgorithmStep 3 : display GPU

VertexShader

FragmentShader

FragmentShader

Record information

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AlgorithmStep 3 : display GPU

VertexShader

FragmentShader

FragmentShader

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AlgorithmSummary

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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ResultsSibenik Cathedral (80K triangles)

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ResultsSponza Atrium (66K triangles)

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ResultsComparison with Radiance

Sponza AtriumSibenik Cathedral

RadianceTime

OurRenderer

Time

Speedup

645 s425 s

13,7 s14,3 s

47,129,7

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ResultsFrom 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

All-Frequency BRDFs

More complex models

Better hemisphere sampling

Multiple bounces

Area light sources

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Any questions?

Radiance Cache Splatting on the web:

http://www.irisa.fr/siames/Pascal.Gautron/