At some point I was super-sampling every pixel, and then it was too slow, so I didn't want it in the inner loop.

At the same time I move the jitter generation outside of `draw()`, then it needs to go into the image class or somewhere else (because the jitter is in world units which are dependent on the pixel size). I'm happy to take suggestions. To be honest, at 6x6 supersampling, jittering doesn't make that much of a difference (But at 2x2 it actually does, a bit)