A Geometry-Based Soft Shadow Volume Algorithm Using Graphics Hardware

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A Geometry-Based Soft Shadow Volume
AlgorithmUsing Graphics Hardware

• Ulf Assarsson
• and
• Tomas Akenine-Möller
• SIGGRAPH 2003

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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

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Intro demo
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A short recap
SOFT
HARD

• Area/volumetric lights give soft shadows
• Real lights have area or volume
• Thus, soft shadows more realistic

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Overview

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

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Hard vs. soft shadows
Two different light source types
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A Real-Time Soft Shadow Volume Algorithm
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Wedges

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

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Two-pass algorithm
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Visibility computation

• Really want to compute how much we can see of the
  light source

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Visibility computation
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Precomputed contribution in 4D textures
contribution area
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How the visibility computation works
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Rasterize a wedge
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A wedge for each silhouette edge
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A wedge for each silhouette edge
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A wedge for each silhouette edge
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A wedge for each silhouette edge
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A wedge for each silhouette edge
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Rasterizing the wedges
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Rasterizing the wedges
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Rasterizing the wedges
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Rasterizing the wedges
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Rasterizing the wedges
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Examples using textured lights
Texture of two colors
Texture of 16 area lights
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Fire Demo
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Fire Demo
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Comparisons
Reference image Our algorithm
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Comparisons
Reference image Our algorithm
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Comparisons
Small light source
Large light source
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Comparisons
512 point lights Our algorithm
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The Last Demo