A Geometry-Based Soft Shadow Volume AlgorithmUsing Graphics Hardware

A Geometry-Based Soft Shadow Volume AlgorithmUsing Graphics Hardware

Ulf Assarsson Ulf Assarsson andand

Tomas AkenineTomas Akenine--MMööllerller

SIGGRAPH 2003SIGGRAPH 2003

We present:We We present: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

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

Intro demoIntro demo A short recap…A A short recapshort recap……

Area/volumetric lights give soft shadows• Real lights have area or volume

• Thus, soft shadows more realistic

Area/volumetric lights give soft shadows• Real lights have area or volume

• Thus, soft shadows more realistic

SOFTHARD

OverviewOverview

Computation of visibility mask:Computation of visibility mask:•• 1st pass: Render hard shadow1st pass: Render hard shadow•• 2nd pass: compensate for overstated umbra2nd pass: compensate for overstated umbra

Hard vs. soft shadowsHard vs. soft shadows

point source

umbra

area source

umbrapenumbra

Two different light source types: Two different light source types:

A Real-Time Soft Shadow Volume AlgorithmA Real-Time Soft Shadow Volume Algorithm

WedgesWedgesWedges

• Each silhouette edge has a corresponding wedge–Provides a piece of penumbra

contribution–Rasterized by pixelshader

• Each silhouette edge has a corresponding wedge–Provides a piece of penumbra

contribution–Rasterized by pixelshader

Two-pass algorithmTwo-pass algorithmVisibility computationVisibility computation

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

Visibility computationVisibility computationPrecomputed contribution in 4D texturesPrecomputed contribution in 4D textures

contributioncontribution areaarea

3232

3232

How the visibility computation works:How the visibility computation works: Rasterize a wedgeRasterize a wedge

A A wedge wedge for for each silhouette edgeeach silhouette edge…… A A wedge wedge for for each silhouette edgeeach silhouette edge……

A A wedge wedge for for each silhouette edgeeach silhouette edge…… A A wedge wedge for for each silhouette edgeeach silhouette edge……

A A wedge wedge for for each silhouette edgeeach silhouette edge…… Rasterizing Rasterizing the the wedgeswedges

Rasterizing Rasterizing the the wedgeswedges Rasterizing Rasterizing the the wedgeswedges

Rasterizing Rasterizing the the wedgeswedges Rasterizing Rasterizing the the wedgeswedges

Examples using textured lightsExamples using textured lights

TextureTexture of 16 area of 16 area lightslights Texture Texture of of two colorstwo colors

Fire DemoFire Fire DemoDemo

Fire DemoFire Fire DemoDemo ComparisonsComparisonsComparisons

Reference Reference image image Our algorithmOur algorithm

ComparisonsComparisonsComparisons

Reference Reference image image Our algorithmOur algorithm

ComparisonsComparisonsComparisons

Small Small light light

sourcesource

Large Large light light

sourcesource

ComparisonsComparisonsComparisons

512 512 point lights Our algorithmpoint lights Our algorithm

The Last DemoThe Last Demo