1. Controlling Memory Consumption of Hierarchical Radiosity with Clustering iMAGIS -GRAVIR/IMAG-INRIA iMAGIS is a joint project of CNRS/INRIA/UJF/INPG Xavier Granier George Drettakis Graphics Interface 99

2. iMAGIS Graphics Interface 99 Overview  Motivation and Previous Work  New Framework  Reduce memory used by links  Reduce memory used by hierarchy  Memory Control Mechanism  Results  Conclusion

3. iMAGIS Graphics Interface 99 Overview  Motivation and Previous Work  New Framework  Reduce memory used by links  Reduce memory used by hierarchy  Memory Control Mechanism  Results  Conclusion

4. iMAGIS Graphics Interface 99 Motivation  Global illumination of large scenes  Hierarchical Radiosity with Clustering [Sil95,SAS94]  fast global illumination  view-independent  High memory consumption due to:  Link structure [WH97]  Hierarchy structure (clusters, subdivided polygons)

5. iMAGIS Graphics Interface 99 Hierarchical radiosity   Multi-resolution representation of exchanges  Clustering

6. iMAGIS Graphics Interface 99 Three hierarchy traversals  Refinement :  build the hierarchy  create link: store information of the exchanges  Gather :  compute irradiance due to links I i =  links on i F ij B k j  Push-Pull  Descend hierarchy : sum the irradiances  Leaves: reflect entire irradiance  Returning : update the hierarchical representation

7. iMAGIS Graphics Interface 99 Hierarchical radiosity B = 0 B = E 22 11

8. iMAGIS Graphics Interface 99 Refinement

9. iMAGIS Graphics Interface 99 Gather I 1 = F 1 *E I += I 1

10. iMAGIS Graphics Interface 99 Push-Pull : Descend I2I2 I1I1 I 1 += I 2

11. iMAGIS Graphics Interface 99 Push-Pull : Return B 1 =  1 *I 1 B = (  A i B i )/A

12. iMAGIS Graphics Interface 99 Previous work  Progressive refinement [CCWG88]  Lack of global error control  Memory used by links  Study by Willmott and Heckbert [WH97]  Getting rid of Links [SSSS98]  unshot radiosity  link cache

13. iMAGIS Graphics Interface 99 Shooting Algorithm [SSSS98]  Shooting algorithm  B 0 = E (sources)  B 0 = 0 (others)  Theoretically the same as standard algorithm  Convergence : global error

14. iMAGIS Graphics Interface 99 Shooting algorithm B = 0  B = 0 B = 0  B = 0 B = E  B = E 22 11

15. iMAGIS Graphics Interface 99 1 st Iteration 22 11 B =  2 * I 2  B =  2 * I 2 B = 0  B = 0 B = E  B = 0

16. iMAGIS Graphics Interface 99 2 nd iteration 22 11 B =  2 * I 2  B = 0 B =  1 * I 1  B =  1 * I 1 B = E  B = 0

17. iMAGIS Graphics Interface 99 3 th iteration 22 11 B =  2 * (I 2 +I 3 )  B =  2 * I 3 B =  1 * I 1  B = 0 B = E  B = 0

18. iMAGIS Graphics Interface 99 Overview  Motivation and Previous Work  New Framework  Reduce memory used by links  Reduce memory used by hierarchy  Memory Control Mechanism  Results  Conclusion

19. iMAGIS Graphics Interface 99 Goals of New Framework  Reduce both link and hierarchy memory consumption  Low speed penalty  Maintain global representation

20. iMAGIS Graphics Interface 99 New Framework for Memory Reduction  Goal  Keep only links needed in next iteration  Algorithm  Unshot radiosity [SSSS98]  B = B i+1 - B i  Merge radiosity steps  Traverse Link Hierarchy

21. iMAGIS Graphics Interface 99 New Framework for Memory Reduction  Link Hierarchy and Traversal  Allows reduction of stored links  Reduce links creation number of links  Remove links where possible  Merge radiosity steps  Facilitates reduction of memory used by radiosity hierarchy ...allows us to move links “higher” in the hierarchy  Enables effective memory control mechanism

22. iMAGIS Graphics Interface 99 Link hierarchy [DS97]  Active link = hierarchy leaf  Passive link = hierarchy node Is the father of

23. iMAGIS Graphics Interface 99 Overview  Motivation and Previous Work  New Framework  Reduce memory used by links  Reduce memory used by hierarchy  Memory Control Mechanism  Results  Conclusion

24. iMAGIS Graphics Interface 99 Link Memory Reduction  Only create links when needed  Merge Refine and Gather  Creation Criterion:  First approach : Don’t store links from sources  More sophisticated approaches possible  Control link creation using a cache mechanism  Predict link utility in future iterations

25. iMAGIS Graphics Interface 99 create gather create and gather refine Refine And Gather - schema source  Active link = hierarchy leaf  Passive link = hierarchy node

26. iMAGIS Graphics Interface 99 Link reduction summary  New approach reduces memory used by links  No overall control of memory  Now, hierarchy uses most of the memory

27. iMAGIS Graphics Interface 99 Overview  Motivation and Previous Work  New Framework  Reduce memory used by links  Reduce memory used by hierarchy  Memory Control Mechanism  Results  Conclusion

28. iMAGIS Graphics Interface 99 Hierarchy storage reduction  Goal: reduce memory during refinement  Otherwise we cannot control overall memory usage  Full recursion on link hierarchy  Refine, Gather and Push Pull method  Hierarchy simplification

29. iMAGIS Graphics Interface 99 Refine, Gather And PushPull  We have to do only one PushPull  For each hierarchy element  For each iteration  Receiver refinement  Refine gather and push pull on each child  Source refinement  Refine gather and push pull on last child  Else refine gather  Replace hierarchy on which no links arrive

30. iMAGIS Graphics Interface 99 create and gathercreate and gather + push pull gatherrefine and push pull gather and push pull Refine Gather and PushPull source  Active link = hierarchy leaf  Passive link = hierarchy node

31. iMAGIS Graphics Interface 99 create Refine Gather and PushPull source replacement  Active link = hierarchy leaf  Passive link = hierarchy node

32. iMAGIS Graphics Interface 99 Texture replacement + 

33. iMAGIS Graphics Interface 99 Hierarchy reduction summary  Advantages  Reduce subdivision due to direct light  But  still a memory peak  Need a mechanism to limit memory

34. iMAGIS Graphics Interface 99 Overview  Motivation and Previous Work  New Framework  Reduce memory used by links  Reduce memory used by hierarchy  Memory Control Mechanism  Results  Conclusion

35. iMAGIS Graphics Interface 99 Memory control mechanism  Control link memory  Move links higher in the element hierarchy  Increase texture replacement  “Cache”-like test  Estimate the expected depth of Link hierarchy

36. iMAGIS Graphics Interface 99 Overview  Motivation and Previous Work  New Framework  Reduce memory used by links  Reduce memory used by hierarchy  Memory Control Mechanism  Results  Conclusion

37. iMAGIS Graphics Interface 99 Tests scenes Medium hall 4 blocks - 169 K Polygons

38. iMAGIS Graphics Interface 99 Tests scenes Simple hall 2 blocks - 65 K polygons complex hall 16 blocks - 676 K polygons

39. iMAGIS Graphics Interface 99 Memory used by HRC

40. iMAGIS Graphics Interface 99 New algorithm (texture replacement)

41. iMAGIS Graphics Interface 99 Cluster reduction

42. iMAGIS Graphics Interface 99 Overview  Motivation and Previous Work  New Framework  Reduce memory used by links  Reduce memory used by hierarchy  Memory Control Mechanism  Results  Conclusion

43. iMAGIS Graphics Interface 99 Summary  New framework for controlling memory  Using Link Hierarchy  Merge all steps of the radiosity solution  Memory control mechanism  Change => Use memory where it’s needed

44. iMAGIS Graphics Interface 99 Future Work  Store part of hierarchy on disk  load only the parts needed in memory  Better representation for simplified clusters  image based rendering  volumetric primitives  multi-resolution geometric simplification  More sophisticated memory control mechanisms  take the memory of hierarchy into account