So, I'm using glReadPixels(...) to get data for a screenshot. I would really like to be able to get data from any framebuffer. Currently, though, I can only get data from the screen framebuffer (or GL_COLOR_ATTACHMENT0_EXT). I looked at glReadBuffer. I'm using PyGame and PyOpenGL, and glGetString(GL_READ_BUFFER) returns None. glReadBuffer(GL_BACK) crashes.
What's going on?