1. 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

2. Outline
Motivation
System
Results
Conclusion

3. Highly Detailed Surfaces

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

5. Quad-fragment Shading

6. Quad-fragment Shading
How many shadings occur per pixel?

7. Pixels at triangle boundaries are shaded multiple times
Over Shade

8. Pixels at triangle boundaries are shaded multiple times

9. Over-shade in GPU pipeline

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

11. Quad-fragment Merging Pipeline
Reduce # of quad-fragments

12. Merging Process

13. Anti-aliasing Effect
Triangle Mesh Final Pixels
Anti-aliasing

14. Aliasing Effect on Naive Merging
Triangle Mesh Final Pixels
Aliasing

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

16. Conditions for Merging

17. Visual Quality
Merging No merging

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

19. Merging vs No merging

20. Result Scene

21. Merging vs No merging

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

23. Q & A
Thank You