SIGGRAPH 2010

Reducing Shading on GPUsUsing Quad-Fragment Merging

Kayvon Fatahalian Solomon Boulos James Hegarty

Kurt Akeley William R. Mark Henry Moreton Pat Hanrahan

JAEHYUN CHO

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Outline

● Motivation

● System

● Results

● Conclusion

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Highly Detailed Surfaces

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GPU Rendering Pipeline

● Quad-fragments● Fragments in 2 x 2 pixel blocks● Quad pipeline in current GPUs

● Generate quad-fragment per triangle

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Quad-fragment Shading

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Quad-fragment Shading

How many shadings occur per pixel?

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Pixels at triangle boundaries are shaded multiple times

Over Shade

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Pixels at triangle boundaries are shaded multiple times

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Over-shade in GPU pipeline

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Main Idea

● Goal● Shade once per pixel

● Solution● Merge quad-fragments

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Quad-fragment Merging Pipeline

Reduce # of quad-fragments

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Merging Process

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Anti-aliasing Effect

Triangle Mesh Final Pixels

Anti-aliasing

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Aliasing Effect on Naive Merging

Triangle Mesh Final Pixels

Aliasing

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Conditions for Merging

● Triangles should be connected via edges

● Triangles have the same sideness● Either front or back-facing

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Conditions for Merging

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Visual Quality

Merging No merging

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Shading Computations

Merging No merging

● 1/2 pixel size triangles● Merging : 8.5x less shading

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Merging vs No merging

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Result Scene

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Merging vs No merging

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Conclusions

● Contribution● Faster than No merge GPU rendering● No radical changes to current pipeline

● Limitation● Motion/focal blur

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Q & A

Thank You