They have very different purpose, so make things easier to work
with by having multiple directories.

Some platforms draw directly to the screen, which means that updates
will flicker if we draw multiple layers. Prevent this by first
composing the update on a hidden surface.

This will allow us to render more things than just the framebuffer.

Some platforms impose a significant delay per frame, so we need
to separate that from the time spent shuffling pixels.

The complex logic waiting for events didn't result in any added
performance, so use the simpler approach.