I still want to make a proper write-up of this program, but for now a brief video with some commentary will do (mostly as a reminder to me!).
The source is here: https://github.com/cheydrick/GTKPixBufTest
Now that I have a basic grip on timed events and pixel buffers I might try for something more ambitious. The only thing standing in the way of that is my poor understanding of the best way to organize non-trivial applications that use GTK. You get punished if you code from the hip with a UI framework.