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AGP Texture Download Problem Revealed
EconolineCrush writes "The latest high-end graphics cards are capable of rendering games at 1600x1200 in 32-bit color at jaw-dropping frame rates, but that might be all they're good for. For all their gaming prowess, all of these cards have horrific AGP download speeds that realize only 1/100th of their theoretical peak. This article lays it all out, testing video cards from ATI, Matrox, and NVIDIA, and clearly illustrates just how bad the problem is. While these cards have no problems rendering images to your screen, you're out of luck if you want to capture those images with any kind of reasonable frame rate via the AGP bus."
I'd certainly expect the AGP bus to be used asymmetrically, how often do you want to do high speed data capture with a card that's primarily output?
The only situation I can see where you'd want more than PCI bandwidth returning would be for uncompressed HDTV capture, and there are better ways to do that (grab the raw broadcast stream for example)
-Yarn - Rio Karma: Excellent
In any event, there's another issue he doesn't really touch upon; while he mentions that a single frame at 1600x1200@32bit colour is 7.5MB, he ignores the fact that a 30fps movie would require (30*7.5)=225MB per second uncompressed; you either have to have that much disk bandwidth or have enough CPU grunt to compress that on the fly. I guess a dedicated MPEG encoder card could help, but your average box is going to have trouble keeping up with on-screen gibs, rocket trails and blood splatters and encoding video.
This would affect everyone in a different way though. TV stations and production sets, even public access TV, along with low budget movies, would be able to use their PCs with a Radeon 9700 or NV30 card to produce their content. They could not only reproduce many of the effects from movies like Toy Story (notably excluding ray tracing), but do it in real-time for instant feedback, meaning much much faster production cycles. This has the potential to make a big impact.
Hmmm. Close but still not quite right. Think of the colour space as a cube with RGB as the three axis of the cube. In 32bit colour you have 8 bits per colour plane, giving you a cube that is 256 x 256 x 256. Any gradient from any point on the cube to any other point on the cube is going to be a maximum of 443 (if my maths is freaked out - distance from two opposite corners of the cube). Plus some messing about with the various quantisation that this line will pass through gives you definite banding on all but the lowest resolution displays...
The only Good System is a Sound System
That's what render-to-texture is for, you don't need to read data back to the CPU.
b) split world/image-space occlusion culling.
This wouldn't be too useful for realtime graphics anyways, because of the way the 3D graphics pipeline works. The CPU can already be processing data a few frames ahead of what the GPU is currently working on. If you read back data from the card every frame, you have to wait for the GPU to finish rendering the current frame before you can start work on the next one.