Many thanks all.
Mustang, from this...
I believe the requirements for a model can be worked out as a 2 bytes (FP16) for each coordinate of the vertex, plus the same for normals, which should put it at 12 bytes per vertex. Using vertex colour probably adds 4 bytes onto that. however, these shouldn't need to all fit into VRAM. The system RAM<>VRAM bus (AGP or PCI-E) carries over traffic for anything needed by the GPU but not present in VRAM, such as textures and vertex info. The CPU feeds the GPU vertex lists over this connection and I don't think that data needs to be cached on the VRAM, though of course if you have enough VRAM to fit everything you'd potentially get a super speed boost. Except for the work the CPU is doing such as transforming vertices as part of an animation. In those cases you'll either be CPU bound or GPU bus bound I think.
So for optimum performance, the more VRAM the better, but to determine the *bare minimum requirements*, I don't think much more than the buffers are needed with a little spare to fit textures.
Mustang, from this...
And you have other stuff there in the VRAM too (depending what 3D-engine you use etc), like vertexes, indexes and geometry which take variable amount of space. You should reserve some VRAM for those, maybe 5-10 megs...
I believe the requirements for a model can be worked out as a 2 bytes (FP16) for each coordinate of the vertex, plus the same for normals, which should put it at 12 bytes per vertex. Using vertex colour probably adds 4 bytes onto that. however, these shouldn't need to all fit into VRAM. The system RAM<>VRAM bus (AGP or PCI-E) carries over traffic for anything needed by the GPU but not present in VRAM, such as textures and vertex info. The CPU feeds the GPU vertex lists over this connection and I don't think that data needs to be cached on the VRAM, though of course if you have enough VRAM to fit everything you'd potentially get a super speed boost. Except for the work the CPU is doing such as transforming vertices as part of an animation. In those cases you'll either be CPU bound or GPU bus bound I think.
So for optimum performance, the more VRAM the better, but to determine the *bare minimum requirements*, I don't think much more than the buffers are needed with a little spare to fit textures.