Gotta be sure :)
With the new system mostly up and running (just bsp rendering and
descriptor sets/layout handling to go, and they're independent of the
old render pass system), the old system can finally be cleared out.
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).
It's a bit flaky for particles, especially at higher frame rates, but
that's due to supporting only 64 overlapping pixels. A reasonable
solution is probably switching to a priority heap for the "sort" and
upping the limit.
