stereo screenshot app

Hello all.
I’m digging up a little project that I abandoned a while ago. I’m trying to create an application that can take screenshots of stereo apps. The idea is that the user can select a window with the mouse and get a two image files, one for each channel.

My problem is accessing the targeted app’s framebuffer. Any tips on how to do this?
I’ve read something about openGL contexts sharing drawables, so I thought this would be the way to go. I would create a new context and attach it to the same window that the target app is using. Then we would be sharing buffers (I think). However, I may be totally on the wrong track since the docs to glXCreateContext say that
“all rendering contexts that share a single display-list space must themselves exist in the same address space”
This means they must be threads of the same process, right? Any help will be appreciated.


Does anyone think doing this is even possible?