I had debated putting the blending in the compose subpass or a separate
pass but went with the separate pass originally, but it turns out that
removing the separate pass gains 1-3% (5-15/545 fps in a timedemo of
demo1).
Lighting doesn't actually do lights yet, but it's producing pixels.
Translucent seems to be working (2d draw uses it), and compose seems to
be working.