1. Interactive Rendering of Translucent Deformable Objects Tom Mertens 1, Jan Kautz 2, Philippe Bekaert 1, Hans-Peter Seidel 2, Frank Van Reeth 1 1 2

2. Overview Goal Previous work Translucency model Our method Implementation Discussion, results and future work

3. Problem: Translucency BRDFBSSRDF

5. Previous work Jensen et al. (SIGGRAPH ’01): –BSSRDF model Jensen et al. (SIGGRAPH ’02): –fast, production quality rendering Lensch et al. (PG ’02), Hao et al. (GI ’03), Carr et al. (GHW’03), Sloan et al. (SIGGRAPH’02-’03): –interactive, real-time rendering with precomputation Our paper: –interactive rendering –varying geometry and material (no precomputation)

6. BSSRDF model function of distance introduced by Jensen et al. (SIGGRAPH’01) multiple scattering materials with high albedo: marble, milk, wax, skin,…

7. BSSRDF model function of distance introduced by Jensen et al. (SIGGRAPH’01) multiple scattering materials with high albedo: marble, milk, wax, skin,…

8. Integrating the BSSRDF hierarchical approach (Jensen et al. ‘02) –decouple light and surface sampling, –decouple light sampling from geometry –2-pass method: irradiance sampling – integration with octree –limitation: rebuilding samples & octree our method –integration ~ hierarchical radiosity mesh based: beneficial for geometry updates hierarchy = clustered triangles form factor for BSSRDF: fast local integration

9. Our Method boundary element method

10. Our Method boundary element method discretized irradiance discretized radiance

11. Our Method boundary element method form factor discretized irradiance discretized radiance

12. example

13. sample irradiance

14. pull irradiance

15. link roots

16. subdivide link

17. subdivide link again

18. gather

19. push

20. Hierarchical Evaluation hierarchy = clustered triangles –tree hierarchy subdivision: 4-to-1 splits face clustering evaluation ~ hierarchical radiosity 1.irradiance sampling + pull 2.construct link hierarchy 3.gather over each link 4.push + average at vertices “oracle” = solid angle interactions at different levels –speed advantage

21. Form Factor: (mid)point to triangle semi-analytical –Taylor expansion advantages: –fast –accurate –noiseless indispensable for local integration more distant: 1 sample area integral integral over edges recursive midpoint

22. Form Factor: point to triangle semi-analytical –Taylor expansion advantages: –fast –accurate –noiseless indispensable for local integration more distant: 1 sample

23. Form Factor: point to triangle semi-analytical –Taylor expansion advantages: –fast –accurate –noiseless indispensable for local integration more distant: 1 sample point samplingform factor

24. Implementation stored links –incremental updates –promote/demote links –real-time frame rate render on-the-fly –instant feedback –less memory overhead –interactive frame rate irradiance –point light (+ shadow) –environment map GPU –fresnel –tone mapping –shadow map

25. Results 5-10 fps for 10-20K tris models –dual Xeon 2.4Ghz; ATI Radeon 9700 Demo video material changecandle twistshadow leakPerlin noise deformation

30. Discussion practical technique for interactive applications speed advantage over previous hierarchical algorithm: –gathering in higher levels –efficient local integration –consistent hierarchy after deformation limitation = mesh –needs hierarchy –limited by resolution –fixed topology interactive applications often mesh-based anyway

31. Future Work recycle radiosity techniques –adaptive meshing, high order interpolation,… –improved oracle function varying topology full GPU implementation non-homogeneous media

32. Acknowledgements Jens Vorsatz (mesh hierarchies) P. Debevec (light probes) funding: –European Regional Development Fund –Marie Curie doctoral fellowship