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?

>>2
Of course, that's right. At first I was hesitant to consider this route because I wasn't sure if it would give me access to the "raw" bitmap info I needed, as in a typical framebuffer, but opening specific processes might actually be more useful to me.

>>3
This is clever and in line with the idea of the project. Actually writing or modifying a device driver would be ideal, but of course I can't write a fucking video card driver. I've never done kernel programming, and for the sake of the project I'd like to do this on a windows machine. I'm sure there's a concept of a LKM in Windows but I can't seem to find anything like it; everything I find that's related redirects me to information about programming device drivers.


I'm also wondering about DLL hooking. Maybe I could get something useful out of hooking a process from ddraw or opengl, or maybe gdi, although I don't have much experience with that, either.  Thoughts?