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Raytracing Prefiltered Occlusion for Aggregate Geometry
Lacewell, D., Burley, B., Boulos, S. and Shirley, P.IEEE Symposium on Interactive Raytracing, 2008
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Chasing Performance
• Faster hardware
• Faster single-ray intersection
• Fewer samples
• Importance sampling
• Prefiltering
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Soft Shadows (2M tris)
Standard, 4 rays Prefiltered, 9 rays Standard, 25 rays
112 seconds 74 seconds 704 seconds
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Bounding Volume Hierarchy
- O(log N) ray intersection
- O(N) update
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Early Ray Termination
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Early Termination (opaque boxes)
Triangles Opaque boxes
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Bottom-up Prefiltering
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Bottom-Up Prefiltering
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Correlation Height
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Correlation Height
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Correlation Height
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Early Termination (opaque boxes)
Triangles Opaque boxes
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Early Termination (prefiltered boxes)
Triangles Prefiltered boxes
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Prefiltered (converged), 81 rays
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Regular, 81 rays, 3x slower
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Regular, 169 rays, 6x slower
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Variance Measurement
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Cost of Transparency
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Soft Shadows (5M tris)
Standard, 9 rays Prefiltered, 9 rays Standard, 49 rays
64 seconds 87 seconds 339 seconds
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Ambient Occl. (3.8M triangles)
Standard, 9 rays Prefiltered, 9 rays Standard, 36 rays
106 seconds 66 seconds 420 seconds
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When to Update?
• Whenever BVH is updated
• Independent of lights
• No update for instances
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Memory Usage per Node
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Total Mem. Usage (GB) 3x3 Cubemap per Node
0
0.5
1
1.5
2
2.5
3
3.5
4
Bush(2M) Tentacles(3.8M)
Bamboo(5M)
OriginalPrefiltered
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Reference
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3x3 Cubemap
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DC (average of 3x3 cubemap)
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DC (ortho average)
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Ad-hoc
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Reference
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12x12 Cubemap
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DC (average of 12x12 cubemap)
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Conclusion
• Simple to implement
• Two runtime speedups:
• Stop descending early
• Less noise ==> Fewer rays
• O(N) update
• DC average often suffices
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Short-Term Future Work
• Faster prefiltering
• Quantization
• Out of core scenes
• Indirect diffuse
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Longer-Term Future Work
Automatically classify geometry:
• Nice mesh [Razor]
• Aggregate and random [current paper]
• Determine “correlation height”
• Aggregate but not random [R-LOD?]
• Buildings, vehicles, etc.