Comment 2 for bug 1660269

I think this is pretty simple in theory. Using desktop GL you could just read the back/front buffers. Using ES you can't do that, but you can render every frame to an FBO and then to the screen. And I believe GLES is happy to read pixels from an FBO (that's how our current casting works).

So really the FBO approach just needs to be merged into the GL renderer. Then it will be capable of reading its own output and providing a software buffer of the latest frame, and many other potentially fun things.