Shadow Volumes on ProgrammaShadow Volumes on Programmable Graphics Hardwareble Graphics Hardware

Speaker: AlvinSpeaker: Alvin

Date: 2003/11/3Date: 2003/11/3

EUROGRAPHICS 2003EUROGRAPHICS 2003

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OutlineOutline

MotivationMotivation Silhouette DetectionSilhouette Detection Generation of Shadow VolumesGeneration of Shadow Volumes ImplementationImplementation ResultResult Conclusion & Future WorkConclusion & Future Work

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MotivationMotivation

Consistent precision.Consistent precision. Objects can be used with vertex shader.Objects can be used with vertex shader. Gain more CPU time.Gain more CPU time. No longer needs to synchronize.No longer needs to synchronize. Silhouette extraction is speed up.Silhouette extraction is speed up. Becomes very simple.Becomes very simple.

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Silhouette DetectionSilhouette Detection

Input Mesh

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Generation of Shadow VolumesGeneration of Shadow Volumes

Each vertex has a total of three indices and Each vertex has a total of three indices and one flag.one flag.– Two indices referring to the world space Two indices referring to the world space

coordinates of the edge’s two end points.coordinates of the edge’s two end points.– One index referring to the silhouette flag and One index referring to the silhouette flag and

the vertex-ordering for the given edge.the vertex-ordering for the given edge.– A flag indicating whether the vertex lie on the A flag indicating whether the vertex lie on the

edge or extruded to infinity.edge or extruded to infinity.

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Generation of Shadow VolumesGeneration of Shadow Volumes

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Shadow Volumes on Programmable Shadow Volumes on Programmable Graphics HardwareGraphics Hardware

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ImplementationImplementation

On ATI Radeon 9700 card using OpenGL.On ATI Radeon 9700 card using OpenGL. Uses a floating point RGBA offscreen buffer.Uses a floating point RGBA offscreen buffer. Supports up to 12 light sources.Supports up to 12 light sources. ProposePropose

– Texture access during vertex processing.Texture access during vertex processing.– A fast, on the card copy from frame buffer to a A fast, on the card copy from frame buffer to a

vertex attribute array.vertex attribute array.

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ResultResult

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ResultResult

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Conclusion & Future WorkConclusion & Future Work

Perform silhouette detection in hardware.Perform silhouette detection in hardware. The shadowing objects can be transformed The shadowing objects can be transformed

by vertex shader.by vertex shader. Buffer read-back are already visible in Buffer read-back are already visible in

OpenGL 2.0 specification.OpenGL 2.0 specification. Solve the near/far plane intersection Solve the near/far plane intersection

problem.problem. NPRNPR