This obsoletes #1111 and #2445, since @ColonisationCaptain and @temhotaokeaha haven't replied to #2373.
I believe that both of those PRs would be fine to keep, but they're even more fine to keep now :)
This is a rebase of StarArawns PBR work from #261 with IngmarBitters work from #1160 cherry-picked on top.
I had to make a few minor changes to make some intermediate commits compile and the end result is not yet 100% what I expected, so there's a bit more work to do.
Co-authored-by: John Mitchell <toasterthegamer@gmail.com>
Co-authored-by: Ingmar Bitter <ingmar.bitter@gmail.com>
