Precomputed Shadow Fields for Dynamic Scenes

1. Microsoft Research Asia Precomputed Shadow Fields for Dynamic Scenes Kun Zhou Yaohua Hu Stephen Lin Baining Guo Heung-Yeung Shum 1

2. Outline • Introduction • Method Overview •Detail • Results

3. • Introduction • Method Overview • Detail • Results

4. Introduction Soft Shadow: multiple shadow maps -[Heckbert and Herf] 1997 Exntnd shadow volume -[Assarsson and Akenine-Moller] 2003 Fake approach -[Chan and Durand] 2003

5. Introduction Why this is not good? For a dynamic scene: -scene complexity -recomputed for each frame For illuminants: -point-like or small light source 5

6. Introduction PRT (Precomputed Radiance Transfer): based on two main assumptions: 1.all objects in the scene are non-emitters 2.the incoming light direction is independent with the position of a point x 6

7. Introduction PRT (Precomputed Radiance Transfer): These spherical functions can be compressed by using some basis functions: Spherical harmonics Wavelet 7

8. Introduction 8

9. • Introduction • Method Overview • Detail • Results

10. Method Overview 10

11. Method Overview Compute Incoming radiance of each point 11

12. Method Overview Compute Occlusion Field for each Object 12

13. Method Overview Compute Occlusion Field for each Object 13

14. Method Overview Compute Occlusion Field for each Object 14

15. Method Overview Compute Occlusion Field for each Object 15

16. Method Overview Compute radiance field for each Light Source 16

17. Method Overview Compute Radiance Field for each Light Source 17

18. Method Overview multiply these and self-visibility at the point together => Incident radiance distribution 18

19. Method Overview Combine with the BRDF to get the final radiance at the point 19

20. Method Overview Combine with the BRDF to get the final radiance at the point 20

21. • Introduction • Method Overview •Detail • Results

22. Detail SRF and OOF Precomputation 22

23. Detail Data Sampling For low frequency shadow: 16 concentric spheres For all frequency shadow: 32 concentric spheres Intermediate points: trilinear interpolation with 8 nearest samples 23

24. Detail Data Compression How? approximate the function using basis functions 24

25. Detail Data Compression For low frequency shadow: Spherical harmonics 25

26. Detail Data Compression Spherical harmonics reconstruction 26

27. Detail Data Compression Spherical harmonics has two properties: 1.Rotationaly invariant 2.Integrating the product of two SH functions = a dot product of their coefficients. 27

28. Detail Data Compression For all frequency shadow: Wavelet Basis 28

29. Detail Data Compression Spherical harmonics VS Wavelet 29

30. Detail Incident Radiance Computation 30

31. Detail Soft Shadow Rendering Acceleration -Culling -Lazy Occlusion Updating occluders for a specific light source remain unchanged, the cached visibility can be reused 31

32. • Introduction • Method Overview • Detail • Results

33. Results

34. Thank You !