Down with OPP: Other Programs' Pixels

I'm trying to figure out how I can read the graphics output from other programs for the sake of creating (meta) visualizations.

I think the key to this is finding out where the framebuffers are, or somehow accessing them. If I can start drawing bitmaps of framebuffer data from one other (abritrary) program, I'm satisfied.

The thing is, I'm a little over my head. I've never worked with low-level languages before, but the idea of reading other programs' memory seems to necessitate one's use, if only for the sake of bypassing restrictions from a compiler. But I wouldn't know how to start looking for framebuffers in memory. (Come to think of it, I've never looked for anything in memory before, at least memory I didn't allocate myself.) There is an assembly language for GPUs by OpenGL.

I've also run across Cg and GLSL in my research, which look awesome for making shaders, but I don't know if they'll help me do this specific task.

Any ideas?

i don't know much about graphics, infact, i know nothing.
but if i was in your situation i would write a kernel module that hooks the device and modifies any data before it hits the real driver.
if you've never done any kernel programming, then lol, good luck.