I understand how to write OpenGL/DirectX programs, and I know the maths and the conceptual stuff behind it, but I'm curious how the GPU-CPU communication works on a low level.
Say I've got an OpenGL program written in C that displays a triangle and rotates the camera by 45 degrees. When I compile this program, will it be turned into a series of ioctl-calls, and the gpu driver then sends the appropriate commands to the gpu, where all the logic of rotating the triangle and setting the appropriate pixels in the appropriate color is wired in? Or will the program be compiled into a "gpu program" which is loaded onto the gpu and computes the rotation etc.? Or something completely different?
Edit: A few days later I found this article series, which basically answers the question: http://fgiesen.wordpress.com/2011/07/01/a-trip-through-the-graphics-pipeline-2011-part-1/