Speaker: Alvin Date: 2003/7/2 SIGGRAPH 2003

1. Interactive Shadow Generation in Complex EnvironmentsNaga K. Govindaraju, Brandon Lloyd, Sung-Eui Yoon, Avneesh Sud, Dinesh Manocha Speaker: Alvin Date: 2003/7/2 SIGGRAPH 2003

2. Outline • Introduction • LOD-based Interactive PVS Computation • Hybrid Shadow Generation Algorithm • Result • Conclusion Interactive Shadow Generation in Complex Environments

3. Introduction • Produce hard-edged shadow. • A hybrid approach. • The efficiencies of image-precision techniques. (Shadow Map) • The image quality of object-space methods. (Shadow Volume) • A interactive algorithm based on LOD and VC to compute PVS. • A novel cross-visibility culling algorithm. • LOD-selection that avoid the artifacts in self-shadow. • In a three PC system. Interactive Shadow Generation in Complex Environments

4. Outline • Introduction • LOD-based Interactive PVS Computation • Hybrid Shadow Generation Algorithm • Result • Conclusion Interactive Shadow Generation in Complex Environments

5. LOD-based Interactive PVS Computation • Key Words • Scene Graph Representation • Occlusion Culling • Problems Interactive Shadow Generation in Complex Environments

6. Key Words • PVS –Potentially Visible Set. • PVSE– The PVS from the eye-view. • PVSL– The PVS from the light-view. • HLOD –Hierarchical Levels-Of-Detail. Interactive Shadow Generation in Complex Environments

7. Scene Graph Representation Each node stores references to its children and to its bounding box. Interactive Shadow Generation in Complex Environments

8. Occlusion Culling • Computing Occlusion Representation (OR) • Render the PVS from the previous frame but based on the current camera location. • Generate a depth map. • Scene Graph Culling (SGC) Given the OR to use OQ. • Object Culling – LOD selection. • Sub-object Culling – Visible sub-object at the leaf node are added to PVS. Interactive Shadow Generation in Complex Environments

9. Problems • Inaccuracy in Shadow Boundaries • When the distance between a shadow-caster and a shadow-receiver is increased. • When the angle between the shadow-receiver’s normal and the light source direction almost 90o . • Self-Shadows • Ensure that LODL is the same as LODE for objects visible in both the views. Interactive Shadow Generation in Complex Environments

10. Problems • Recomputing PVSL • When the user move, LODE can change. • Need to compute PVSL to avoid self-shadows and popping in the final image. Interactive Shadow Generation in Complex Environments

11. Outline • Introduction • LOD-based Interactive PVS Computation • Hybrid Shadow Generation Algorithm • Result • Conclusion Interactive Shadow Generation in Complex Environments

12. Hybrid Shadow Generation Algorithm • Cross Culling • Shadow Generation • Architecture of The Process-Parallel Algorithm. • Frame Work Interactive Shadow Generation in Complex Environments

13. Cross Culling • Partitions the PVSE into three subsets. • Fully-lighted (FV) • Fully-shadowed receivers (SRF) • Partially-shadowed receivers (SRP) • Proceeds in two step. • Based on OQ, partitions PVSE into FV, SRF, SRP. • Cull away those in PVSL but do not cast a shadow on SRP. The remaining, SC, are used for shadow generation. Interactive Shadow Generation in Complex Environments

14. Shadow Generation • SRP are clipped against the shadow frusta formed by SC. • The resulting shadow-polygons are calculated by repeatedly clipping the scene triangles against the planes of the shadow frusta. Interactive Shadow Generation in Complex Environments

15. Rendering • The shadow are rendered in two passes: • SRF and SRP are rendered with only ambient lighting. The shadowed polygons are rendered to the stencil buffer with the depth test enabled. • SRP and FV are rendered with full lighting using the stencil test to prevent writing in the shadowed regions. Interactive Shadow Generation in Complex Environments

16. Architecture of The Process-Parallel Algorithm Interactive Shadow Generation in Complex Environments

17. Frame Work Interactive Shadow Generation in Complex Environments

18. Outline • Introduction • LOD-based Interactive PVS Computation • Hybrid Shadow Generation Algorithm • Result • Conclusion Interactive Shadow Generation in Complex Environments

19. Result • Experiment Environment • Performance • Snapshot • Demo Interactive Shadow Generation in Complex Environments

20. Experiment Environment • On 3 Dell Precision workstations. • With dual 1.8 GHz pentium CPUs • 2 GB of main memory • A NVIDIA GeForce-4 Ti 4600 GPU • Allocate 72MB out of 128MB on each GPU to store the vertices of objects, sub-objects, and bounding boxes. • Use Vertex Arrays and OQ. Interactive Shadow Generation in Complex Environments

21. Performance Interactive Shadow Generation in Complex Environments

22. Snapshot Interactive Shadow Generation in Complex Environments

23. Snapshot Interactive Shadow Generation in Complex Environments

24. Snapshot Interactive Shadow Generation in Complex Environments

25. Snapshot Interactive Shadow Generation in Complex Environments

26. Demo Interactive Shadow Generation in Complex Environments

27. Outline • Introduction • LOD-based Interactive PVS Computation • Hybrid Shadow Generation Algorithm • Result • Conclusion Interactive Shadow Generation in Complex Environments

28. Conclusion • Generate hard-edge shadow. • Reduce the aliasing artifact that are present in pure image-precision approaches. • Present an improved algorithm for PVS computation. • The Cross-culling algorithm can accelerate the performance of a pure shadow volume approach Interactive Shadow Generation in Complex Environments

29. Thanks for your attention! Interactive Shadow Generation in Complex Environments