Quote:Original post by 3drookie
here's another question...
since the "local video memory" is fast for video card to manipulate, and the video card dedicated to GRAPHICS PROCESS,why bother to use the "AGP memory"?
is that only because the "local video memory" may be not enough for graphic data storage?
Yes. That's one of the main reasons. AGP comes from a time (~10 years ago!) when a typical graphics card would have, say, 2MB of local video memory and a typical PC system had 64-128MB of main system memory, so it made sense to set some system memory aside for situations where there wasn't enough local memory.
In these days of monster graphics cards with 512MB of local video memory, it's less likely used as an overflow.
Another reason is dynamic graphics data - any data that needs to be regularly modified with the CPU is usually better off in AGP memory (it's write combined, but it's local to the CPU too, so uses less CPU time to access)
Quote:what role does the CPU play in the process of graphics??
Not very much these days. Mostly application-side jobs like writing vertex data into locked buffers, object culling, traversing scene graphs, loading resources into main memory, things like that.
On the D3D and device driver side: handling the D3D API, swizzling and other conversion when some types of resources are locked/unlocked , and setting up the command buffer for the GPU.<br><br>Before hardware T&L, the CPU also handled all vertex processing.<br><br>The fact that modern GPUs now handle so much of the graphics pipeline makes avoiding unnecessary serialization between CPU and GPU all the more important (i.e. stalls where one has a resource locked and the other wants to use it), thus things like buffer renaming. Serialization between CPU and GPU throws away the GPUs processing ability.
