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n00body

Multiple passes, managing geometry

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____Say I need to render an entire scene 2-3 times. As I see it, I have two options here for dealing with the visible geometry. Either streaming in, and transforming the geometry again for each pass, or storing the transformed geometry in memory and reusing it for all the passes. ____I already know that streaming and transforming multiple times is going to cause a lot of repeated work, but it would save me the constraints of fitting it into memory. Storing it saves work, but consumes a lot of memory and puts a cap on the number of vertices I could have in the scene (even assuming a compressed vertex format). ____I would like some input on the costs and benefits of these two approaches. Other suggestions are also welcome, so long as you explain why their cost/benefits would make them more approachable. Thanks.

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Well, it's going to depend on how much work you need to do to transform your vertices. For complex skinned meshes, it could indeed be a win to skin on the CPU or use some hardware feature (vertex textures, R2VB, MEMEXPORT on the 360, etc.) to pre-transform vertices. This is pretty common for skinned crowd rendering, where you re-use the same pose over and over for many instances. For non-skinned meshes, I really doubt you'd save anything at all by pre-transforming.

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This sounds like a catch-22 to me. If I plan to have a lot of skinned meshes on screen at once, I am better off storing and reusing transformed vertices. However, I'm suddenly limited by the number of vertices I can store in memory, so I can't have a whole lot of skinned meshes on screen.

Can anyone point me to some good examples of handling a lot of skinned geometry in a multipass rendering situation?

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