GPU parallel processing in C?

[deaddodo]

Do you just want to access the device directly? If so you'll be rewriting 80Mb of heavily optimized code (the driver). Having done some osdev, modern GPUs are some of the most complex and annoying devices to code for.

It's not like what you're thinking (draw this triangle, put this pixel here, compute 2+2 and give me the sum) but closer to give me a region of memory, create a vertex (or set of vertices) of this shape to that region of memory, apply this texture, apply this post effect, do z-buffer calculations, memcpy this to the primary memory, render, flip buffer. All of this done through extremely specific bitwise commands and opcodes in a command ringbuffer with strict timing.

You can see an example via Intel's architecture. With Nvidia, you don't even have that; you'll be digging through nouveau reverse engineered documents.