How do you get the color buffer into an array/pointer?
glReadPixels, but beware that this isn’t going to be very fast.
I know; I am trying to use it to do antialiasing in real-time but glReadPixels runs about 2 FPS.
Current GPUs haven’t been designed with readbacks in mind, that’s the cause of glReadPixels being so slow, tilebased renderes do much better there.
So the best choice for doing AA by yourself would be to render the whole scene to a texture and then apply a shader to that texture where you do your own AA and then output that texture to screen.