> This question pops up every once in a while. A few years ago I looked
> through a postscript manual wondering how difficult it would be to build a
> postscript file that crunched RC5 keys when a printer tried to render it.
postscript is essentially forth, after all. Trouble is, most postscript
interpreters are pretty damn slow.
> The latest bleeding edge graphics cards are programmable to a limited
> degree (am I thinking of the ATI Radeon here?) but not nearly programmable
> enough, I'm sure.
NVIDIA's chips are semi programmable too, but a big hurdle is lack of
documentation on the 3D rendering engine. That stuff is trade secret.
I *do* suspect you could use the geometry engine (aka "Transformation
Lighting and Projection") to do large numbers of fixed point 3x3
vector-matrix dot products with limited precision rather quickly. The
question is, how useful would this be? The pipeline is probably such that
you load one matrix and "transform" a large number of x,y,z vectors through
it at a rather high speed. I'm not sure how useful this primitive would be
in doing FFT operations.
The newest Geforce3 chip also has both Pixel Shaders and Vertex Shaders
which are each a SIMD programmable vector processors. The Pixel Shaders
operate on every pixel and generate the actual RGB pixels while the Vertex
Processors operate on the geometry and texture mapping coordinates of the 3D
mesh... I don't know much about these, but pixels are only 8 bits per
component so the pixel processors can't be very wide.
I'm also not sure how fast you can get results OUT of the nvidia memory.
Typically, these cards have 32-64MB of very high speed dedicated DDR SDRAM,
but its optimized for the GPU to write into the memory, and the display
refresh engine to read from it, I don't know how fast results could be read
back into the host system
-jrp
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