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Advanced Out-of-Core Rendering Techniques for Massive Models at The University of Pennsylvania

This project explores advanced techniques in out-of-core rendering and hierarchical level of detail (HLOD) for efficiently rendering complex scenes containing billions of polygons. The work includes procedural modeling, view frustum and occlusion culling, and hardware occlusion queries, presented through high-resolution models such as Pompeii (~1.4 billion polygons) and a Boeing 777 (~350 million polygons). We delve into past research, implementation strategies, and the challenges faced with rendering massive datasets, ultimately contributing to more efficient graphics processing.

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Advanced Out-of-Core Rendering Techniques for Massive Models at The University of Pennsylvania

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  1. Visibility Driven Out-of-Core HLOD Rendering Patrick Cozzi The University of Pennsylvania 00000000 of 01010110

  2. Project History Procedurally generated model of Pompeii: ~1.4 billion polygons. Image from [Mueller06] 00000001 of 01010110

  3. Project History Boeing 777 model: ~350 million polygons. Image from http://graphics.cs.uni-sb.de/MassiveRT/boeing777.html 00000010 of 01010110

  4. Contents • Previous Work • View Frustum and Occlusion Culling • Hardware Occlusion Queries (HOQ) • Level of Detail (LOD) • Hierarchical Level of Detail (HLOD) • Out-of-Core Rendering (OOC) 00000011 of 01010110

  5. Contents Continued • Implementation Work • Vertex Clustering [Rossignac93] • HLOD Tree Creation • Primary Contribution: OOC Rendering • Results • Future Work • Demos throughout 00000100 of 01010110

  6. culled culled culled View Frustum Culling • Can be slower than brute force. When? rendered rendered rendered 00000101 of 01010110

  7. 3 4 5 1 0 2 0 1 3 4 2 5 View Frustum Culling 00000110 of 01010110

  8. 3 4 5 1 0 2 0 1 3 4 2 5 View Frustum Culling 00000111 of 01010110

  9. View Frustum Culling • Demo 00001000 of 01010110

  10. culled Occlusion Culling • Effective in scenes with high depth complexity 0001001 of 01010110

  11. Occlusion Culling • From-region or from-point • Most are conservative • Occluder Fusion • Difficult for general scenes with arbitrary occluders. So make simplifying assumptions: • [Wonka00] – urban environments • [Ohlarik08] – planets and satellites 00001010 of 01010110

  12. Hardware Occlusion Queries • From-point visibility that handles general scenes with arbitrary occluders and occluder fusion • How? • Use the GPU 00001011 of 01010110

  13. Hardware Occlusion Queries • Disable color and depth write Color Buffer Depth Buffer 00001100 of 01010110

  14. Hardware Occlusion Queries • Disable color and depth write • Render BV using HOQ 00001101 of 01010110

  15. Hardware Occlusion Queries • Disable color and depth write • Render BV using HOQ • Enable color and depth writes Color Buffer Depth Buffer 0001110 of 01010110

  16. Hardware Occlusion Queries • Disable color and depth write • Render BV using HOQ • Enable color and depth writes • Render object based on HOQ results 00001111 of 01010110

  17. Hardware Occlusion Queries class IQueryOcclusion { public: virtualvoid Begin() = 0; virtualvoid End() = 0; virtualbool IsResultAvailable() = 0; virtualunsignedint NumberOfSamplesPassed() = 0; virtualunsignedint NumberOfFragmentsPassed() = 0; }; 00010000 of 01010110

  18. Hardware Occlusion Queries class IQueryOcclusion { public: virtualvoid Begin() = 0; virtualvoid End() = 0; virtualbool IsResultAvailable() = 0; virtualunsignedint NumberOfSamplesPassed() = 0; virtualunsignedint NumberOfFragmentsPassed() = 0; }; 00010000 of 01010110

  19. Hardware Occlusion Queries class IQueryOcclusion { public: virtualvoid Begin() = 0; virtualvoid End() = 0; virtualbool IsResultAvailable() = 0; virtualunsignedint NumberOfSamplesPassed() = 0; virtualunsignedint NumberOfFragmentsPassed() = 0; }; 00001000 of 01010110

  20. CPU Drawo1 Drawo2 Drawo3 GPU Drawo1 Drawo2 Drawo3 CPU Queryo1 -- stall -- Drawo1 GPU Queryo1 -- starve -- Drawo1 Hardware Occlusion Queries • CPU stalls and GPU starvation 00010001 of 01010110

  21. Is Culling Enough? 00010010 of 01010110

  22. Is Culling Enough? Now what? 0001011 of 01010110

  23. Is Culling Enough? • Demo 00010100 of 01010110

  24. Level of Detail • Generation: less triangles, simpler shader • Selection: distance, pixel size • Switching: avoid popping • Discrete, Continuous, Hierarchical 00010101 of 01010110

  25. Discrete LOD 3,086 Triangles 52,375 Triangles 69,541 Triangles 00010110 of 01010110

  26. Discrete LOD • Demo 00010111 of 01010110

  27. Discrete LOD Not enough detail up close Too much detail in the distance 00011000 of 01010110

  28. Continuous LOD edge collapse Image from [Luebke01] vertex split 00011001 of 01010110

  29. Hierarchical LOD 1 Node 3,086 Triangles 4 Nodes 9,421 Triangles 16 Nodes 77,097 Triangles 00011010 of 01010110

  30. Hierarchical LOD 1 Node 3,086 Triangles 4 Nodes 9,421 Triangles 16 Nodes 77,097 Triangles 00011011 of 01010110

  31. Node Refinement Hierarchical LOD visit(node) { if (computeSSE(node) < pixel tolerance) { render(node); } else { foreach (child in node.children) visit(child); } } 00011100 of 01010110

  32. Hierarchical LOD 00011101 of 01010110

  33. Hierarchical LOD • New Problem: Cracks 00011110 of 01010110

  34. Hierarchical LOD • Demo 00011111 of 01010110

  35. HLOD + Culling visit(node) { if (node overlaps view frustum) { // ... } } 00100000 of 01010110

  36. HLOD + Culling visit(node) { if (node overlaps view frustum) { render node’s BV with HOQ if (query.NumberOfFragmentsPassed() > 0) { // ... } } } Render front to back! 00100001 of 01010110

  37. HLOD + Culling + VMSSE visit(node) { if (node overlaps view frustum) { render node’s BV with HOQ if (query.NumberOfFragmentsPassed() > 0) { if (computeVMSSE(node, query) < tolerance) { render(node); } else { // ... } } } } 00100010 of 01010110

  38. VMSSE • VMSEE: Virtual Multiresolution SSE • Relative Visibility = # pixels visible / # possible pixels visible • VMSSE = f(SSE, Relative Visibility) 00100011 of 01010110

  39. Optimized HLOD Refinement Driven by HOQs [Charalambos07] • Exploit spatial and temporal coherence for scheduling HOQs. • Predict refinement based on node’s relative visibility from previous frame • VMSSEiest = SSEi * biasi-1 00100100 of 01010110

  40. Optimized HLOD Refinement Driven by HOQs [Charalambos07] • Example prediction • Refinement stopped for this node in previous frame • VMSSEiest < threshold ? Stop : Refine • Stop: • Issue query • Render without checking query 00100101 of 01010110

  41. Implementation Work • 3 HLOD algorithms including [Charalambos07] • Vertex Clustering • HLOD Tree Creation • OOC Rendering • Load/Unload Rules • Rendering • Replacement Policy • Multithreading 00100110 of 01010110

  42. Vertex Clustering [Rossignac93] • Fast: expected O(n) • Robustness: arbitrary topology • Capable of drastic simplification • “Easy to code” • OOC extensions [Lindstrom00] 00100111 of 01010110

  43. 0.8 1. Compute per-vertex weights 2. Assign vertices to clusters 3. Identify highest weighted vertex in each cluster 0.5 0.5 1 1 Vertex Clustering [Rossignac93] 00100111 of 01010110

  44. Vertex Clustering [Rossignac93] 0.8 1. Compute per-vertex weights 2. Assign vertices to clusters 3. Identify highest weighted vertex in each cluster 4. Collapse and remove degenerate triangles 1 1 00101000 of 01010110

  45. Vertex Clustering [Rossignac93] 3,086 Triangles 52,375 Triangles 69,541 Triangles 00101001 of 01010110

  46. Vertex Clustering [Rossignac93] • Questionable Fidelity • Hard to control output • Conservative Error Metric 00101010 of 01010110

  47. HLOD Tree Creation • Input • Model (.ply, .obj) • Target triangles per leaf node • Maximum tree depth • Output • 1 file per node • Normals computed at runtime 00101011 of 01010110

  48. HLOD Tree Creation • Top-down • Root node: Full AABB Lowest Detail 00101100 of 01010110

  49. HLOD Tree Creation • Splitting Planes 2 Planes 3 Planes 00101101 of 01010110

  50. HLOD Tree Creation • Splitting Planes 00101110 of 01010110

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