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A Geometry-Based Soft Shadow Volume Algorithm Using Graphics Hardware

This publication presents a soft shadow volume algorithm that utilizes graphics hardware, enabling real-time performance for realistic soft shadows from area or volumetric light sources. The algorithm balances speed and accuracy trade-offs and includes two-pass computation for visibility masks and precomputed contributions in 4D textures. Examples demonstrate the effectiveness of the algorithm with textured lights and various light source sizes.

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A Geometry-Based Soft Shadow Volume Algorithm Using Graphics Hardware

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  1. A Geometry-Based Soft Shadow Volume AlgorithmUsing Graphics Hardware Ulf Assarsson and Tomas Akenine-Möller SIGGRAPH 2003

  2. We present: A Soft Shadow Volume Algorithm: • Area light sources • Simple volumetric light sources • Textures and short video textures as lights • Real-time performance with programmable graphics hardware • Approximate soft shadows • Trade speed vs accuracy

  3. Intro demo

  4. A short recap… HARD SOFT Area/volumetric lights give soft shadows • Real lights have area or volume • Thus, soft shadows more realistic

  5. Overview Computation of visibility mask: • 1st pass: Render hard shadow • 2nd pass: compensate for overstated umbra

  6. point source area source umbra penumbra umbra Hard vs. soft shadows Two different light source types:

  7. A Real-Time Soft Shadow Volume Algorithm

  8. Wedges • Each silhouette edge has a corresponding wedge • Provides a piece of penumbra contribution • Rasterized by pixelshader

  9. Two-pass algorithm

  10. Visibility computation • Really want to compute how much we can see of the light source

  11. Visibility computation

  12. Precomputed contribution in 4D textures contribution area 32 32

  13. How the visibility computation works:

  14. Rasterize a wedge

  15. A wedge for each silhouette edge…

  16. A wedge for each silhouette edge…

  17. A wedge for each silhouette edge…

  18. A wedge for each silhouette edge…

  19. A wedge for each silhouette edge…

  20. Rasterizing the wedges

  21. Rasterizing the wedges

  22. Rasterizing the wedges

  23. Rasterizing the wedges

  24. Rasterizing the wedges

  25. Examples using textured lights Texture of two colors Texture of 16 area lights

  26. Fire Demo

  27. Fire Demo

  28. Comparisons Reference image Our algorithm

  29. Comparisons Reference image Our algorithm

  30. Comparisons Small light source Large light source

  31. Comparisons 512 point lights Our algorithm

  32. The Last Demo

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