Reducing Shading on GPUs Using Quad-Fragment Merging JAEHYUN CHO SIGGRAPH 2010 Reducing Shading on GPUs Using Quad-Fragment Merging Kayvon Fatahalian Solomon Boulos James Hegarty Kurt Akeley William R. Mark Henry Moreton Pat Hanrahan JAEHYUN CHO 1

Outline Motivation System Results Conclusion

Highly Detailed Surfaces

GPU Rendering Pipeline Quad-fragments Fragments in 2 x 2 pixel blocks Quad pipeline in current GPUs Generate quad-fragment per triangle

Quad-fragment Shading

Quad-fragment Shading How many shadings occur per pixel?

Pixels at triangle boundaries are shaded multiple times Over Shade

Pixels at triangle boundaries are shaded multiple times

Over-shade in GPU pipeline

Main Idea Goal Shade once per pixel Solution Merge quad-fragments

Quad-fragment Merging Pipeline Reduce # of quad-fragments

Merging Process

Anti-aliasing Effect Triangle Mesh Final Pixels Anti-aliasing

Aliasing Effect on Naive Merging Triangle Mesh Final Pixels Aliasing

Conditions for Merging Triangles should be connected via edges Triangles have the same sideness Either front or back-facing

Conditions for Merging

Visual Quality Merging No merging

Shading Computations Merging No merging 1/2 pixel size triangles Merging : 8.5x less shading

Merging vs No merging

Result Scene

Merging vs No merging

Conclusions Contribution Limitation Faster than No merge GPU rendering No radical changes to current pipeline Limitation Motion/focal blur

Q & A Thank You