Ptex and Vector Displacement in AMD Demos Karl Hillesland Member of Technical Staff, AMD

1. Ptex and Vector Displacement in AMD DemosKarl HilleslandMember of Technical Staff, AMD

2. Ptex Showings • September 2011 – Press Event • Siggraph Asia 2011 – Sketch • Radeon HD 7970 Launch – Press Event • Modified GL version, won’t discuss

3. Ptex Ptex: Per-face Texture Mapping for Production Rendering [Burley and Lacewell, 2008] • No UV setup (it’s implicit) • No Seams • Per-Patch Resolution Control • Out-of-core Performance Advantages

4. Ptex Ptex: Per-face Texture Mapping for Production Rendering [Burley and Lacewell, 2008] • Per-face textures + MIPs • Adjacency for filtering

5. McDonald and Burley Per-face texture mapping for real-time rendering, McDonald and Burley, SIGGRAPH 2011 Talk. Practical Ptex for Games, John McDonald, Game Developer Magazine, January, 2012

6. Borders for Filtering Face A Texture Face B Texture Kernel Note: Quad centric

7. Borders for Filtering

8. Borders for Filtering

9. Borders for Filtering

10. Packed Ptex Pack in one texture • Includes all MIPs • Sorted by resolution

11. Runtime Shader • Compute atlas location starting with primitive ID and face UV

12. Runtime Shader • Compute desired resolution using ddx and ddy of face UV

13. Runtime Shader • Compute desired resolution using face UV • Clamp to base resolution

14. Runtime Shader • Compute desired resolution using face UV • Clamp to base resolution • Find resolution block

15. Runtime Shader • Compute desired resolution using face UV • Clamp to base resolution • Find resolution block • Find face location

16. Runtime Shader • Compute desired resolution using face UV • Clamp to base resolution • Find resolution block • Find face location • Incorporate face UVfor final UV

17. Constant Buffers • Indexed by resolution • Row (V) offset • Block location • Prefix Sum • Face resolution • Offset in bin • Ours: 20 4-byte values

18. Preprocess • Sort primitives by resolution • Generate packed textures • Generate constant buffers • Prefix sum of resolution count • Row (V) offset for each resolution

19. Texture Compression • Start with at least 2x2 • 2-texel border to get mulitple of 4x4 • Prevents compression across faces

20. Authoring Vector Displacement • Author base mesh • Subdivide and edit • Export Displacement from base

21. Vector Displacement Without Seams • Preprocessing • Border values match • Corners match • Runtime • Constant tessellation for now

22. Demos

23. Time Cost – Displaced Leo • 1920 x 1200 • Albedo, AO, Spec, Normal • Radeon HD 7970 • Wall Clock • Average frame time: 1.3 ms • Average frame cost: ~10 microseconds • Perf Query • Average frame time: 2.8 ms • Average frame cost: 0.6 ms

24. Space Efficiency 37% Black 7% Black 9-23% Borders

25. Problems • GS or Tessellation for per-face UVs • Some sorting restrictions • Indirection solves that at a cost • Anisotropic cost • Ties between geometry and texture • Quads only so far

26. Conclusion • Can actually save memory • Computationally cheap • Most promising for seamless displacement