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

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

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

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)

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

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

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

iMAGIS Graphics Interface 99 Refinement

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

iMAGIS Graphics Interface 99 Texture replacement + 

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

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

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

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

iMAGIS Graphics Interface 99 Tests scenes Medium hall 4 blocks K Polygons

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

iMAGIS Graphics Interface 99 Memory used by HRC

iMAGIS Graphics Interface 99 New algorithm (texture replacement)

iMAGIS Graphics Interface 99 Cluster reduction

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

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

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