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Shadow volumes: make using vertex shader or cpu?

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Something I''ve noticed in a couple shadowing demos, for example, a multiple shadowing demo posted on Gamedev awhile back and in the DX9 SDK, is that they both develop the new vertices for the shadow volume using (I think) the CPU. Wouldn''t it be more efficient however to build the volume using a vertex shader and thereby eliminate the latency between the video card and the CPU?

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There's been a few implementations doing so. Usually they just calculate a few things on the GPU and the rest is done on the CPU


That shows a working implementation calculating volume extrusion on the GPU when available using an OpenGL ARB vertex program.

Hopefully those links help you out, I can't wait until shadow volumes are fully on the GPU in realtime. That should be fun


while (your_engine >= my_engine)

[edited by - gwihlidal on January 5, 2004 9:42:07 PM]

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this depends on the cpu and the gpu usage of your engine.if the cpu is idle then you can make it on the cpu.if you are having heavy AI and physics then you can do it on the gpu to save the cpu.the problem with the cpu expansion is copying of the data each frame to the hardware,while the problem with expanding the shader on the gpu is the no. of vertex shader instructions performed by the card and the polycount of the model should be doubled.you can also see the shadow shader sample of ati (Directx ).they calculate the silhoute and expand the shadow volume using a vertex shader.

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