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

Alivn/GAME LAB/CSIE/NDHU 2 Interactive Shadow Generation in Complex Environments Outline Introduction Introduction LOD-based Interactive PVS Computation LOD-based Interactive PVS Computation Hybrid Shadow Generation Algorithm Hybrid Shadow Generation Algorithm Result Result Conclusion Conclusion

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

Alivn/GAME LAB/CSIE/NDHU 4 Interactive Shadow Generation in Complex Environments Outline Introduction Introduction LOD-based Interactive PVS Computation LOD-based Interactive PVS Computation Hybrid Shadow Generation Algorithm Hybrid Shadow Generation Algorithm Result Result Conclusion Conclusion

Alivn/GAME LAB/CSIE/NDHU 5 Interactive Shadow Generation in Complex Environments LOD-based Interactive PVS Computation Key Words Key Words Scene Graph Representation Scene Graph Representation Occlusion Culling Occlusion Culling Problems Problems

Alivn/GAME LAB/CSIE/NDHU 6 Interactive Shadow Generation in Complex Environments Key Words PVS – Potentially Visible Set. PVS – Potentially Visible Set. PVS E – The PVS from the eye-view. PVS E – The PVS from the eye-view. PVS L – The PVS from the light-view. PVS L – The PVS from the light-view. HLOD – Hierarchical Levels-Of-Detail. HLOD – Hierarchical Levels-Of-Detail.

Alivn/GAME LAB/CSIE/NDHU 7 Interactive Shadow Generation in Complex Environments Scene Graph Representation Each node stores references to its children and to its bounding box.

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

Alivn/GAME LAB/CSIE/NDHU 9 Interactive Shadow Generation in Complex Environments Problems Inaccuracy in Shadow Boundaries Inaccuracy in Shadow Boundaries When the distance between a shadow-caster and a shadow- receiver is increased. 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 90 o. When the angle between the shadow-receiver ’ s normal and the light source direction almost 90 o. Self-Shadows Self-Shadows Ensure that LOD L is the same as LOD E for objects visible in both the views. Ensure that LOD L is the same as LOD E for objects visible in both the views.

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

Alivn/GAME LAB/CSIE/NDHU 11 Interactive Shadow Generation in Complex Environments Outline Introduction Introduction LOD-based Interactive PVS Computation LOD-based Interactive PVS Computation Hybrid Shadow Generation Algorithm Hybrid Shadow Generation Algorithm Result Result Conclusion Conclusion

Alivn/GAME LAB/CSIE/NDHU 12 Interactive Shadow Generation in Complex Environments Hybrid Shadow Generation Algorithm Cross Culling Cross Culling Shadow Generation Shadow Generation Architecture of The Process-Parallel Algorithm. Architecture of The Process-Parallel Algorithm. Frame Work Frame Work

Alivn/GAME LAB/CSIE/NDHU 13 Interactive Shadow Generation in Complex Environments Cross Culling Partitions the PVS E into three subsets. Partitions the PVS E into three subsets. Fully-lighted (FV) Fully-lighted (FV) Fully-shadowed receivers (SR F ) Fully-shadowed receivers (SR F ) Partially-shadowed receivers (SR P ) Partially-shadowed receivers (SR P ) Proceeds in two step. Proceeds in two step. Based on OQ, partitions PVS E into FV, SR F, SR P. Based on OQ, partitions PVS E into FV, SR F, SR P. Cull away those in PVS L but do not cast a shadow on SR P. The remaining, SC, are used for shadow generation. Cull away those in PVS L but do not cast a shadow on SR P. The remaining, SC, are used for shadow generation.

Alivn/GAME LAB/CSIE/NDHU 14 Interactive Shadow Generation in Complex Environments Shadow Generation SR P are clipped against the shadow frusta formed by SC. SR P 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. The resulting shadow-polygons are calculated by repeatedly clipping the scene triangles against the planes of the shadow frusta.

Alivn/GAME LAB/CSIE/NDHU 15 Interactive Shadow Generation in Complex Environments Rendering The shadow are rendered in two passes: The shadow are rendered in two passes: SR F and SR P are rendered with only ambient lighting. The shadowed polygons are rendered to the stencil buffer with the depth test enabled. SR F and SR P are rendered with only ambient lighting. The shadowed polygons are rendered to the stencil buffer with the depth test enabled. SR P and FV are rendered with full lighting using the stencil test to prevent writing in the shadowed regions. SR P and FV are rendered with full lighting using the stencil test to prevent writing in the shadowed regions.

Alivn/GAME LAB/CSIE/NDHU 16 Interactive Shadow Generation in Complex Environments Architecture of The Process-Parallel Algorithm

Alivn/GAME LAB/CSIE/NDHU 17 Interactive Shadow Generation in Complex Environments Frame Work

Alivn/GAME LAB/CSIE/NDHU 18 Interactive Shadow Generation in Complex Environments Outline Introduction Introduction LOD-based Interactive PVS Computation LOD-based Interactive PVS Computation Hybrid Shadow Generation Algorithm Hybrid Shadow Generation Algorithm Result Result Conclusion Conclusion

Alivn/GAME LAB/CSIE/NDHU 19 Interactive Shadow Generation in Complex Environments Result Experiment Environment Experiment Environment Performance Performance Snapshot Snapshot Demo Demo

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

Alivn/GAME LAB/CSIE/NDHU 21 Interactive Shadow Generation in Complex Environments Performance

Alivn/GAME LAB/CSIE/NDHU 22 Interactive Shadow Generation in Complex Environments Snapshot

Alivn/GAME LAB/CSIE/NDHU 23 Interactive Shadow Generation in Complex Environments Snapshot

Alivn/GAME LAB/CSIE/NDHU 24 Interactive Shadow Generation in Complex Environments Snapshot

Alivn/GAME LAB/CSIE/NDHU 25 Interactive Shadow Generation in Complex Environments Snapshot

Alivn/GAME LAB/CSIE/NDHU 26 Interactive Shadow Generation in Complex Environments Demo

Alivn/GAME LAB/CSIE/NDHU 27 Interactive Shadow Generation in Complex Environments Outline Introduction Introduction LOD-based Interactive PVS Computation LOD-based Interactive PVS Computation Hybrid Shadow Generation Algorithm Hybrid Shadow Generation Algorithm Result Result Conclusion Conclusion

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

Alivn/GAME LAB/CSIE/NDHU 29 Interactive Shadow Generation in Complex Environments Thanks for your attention!