tree c12eedaecb958f8e0418da9eb5149dabd3826d82
parent ab350ca7302303b4e05320453b39636c0a4219b6
author Mike Klein <mtklein@google.com> 1541183025 -0400
committer Skia Commit-Bot <skia-commit-bot@chromium.org> 1541186937 +0000

DeMorgan's blend-on-black logic

I kept reading and re-reading the existing logic and couldn't figure it
out until I looked at the AlphaOption enum.  I think this direction
reads a bit more clearly.

(This is why we have those ->premul methods.  Oddly, we fail for 4444.)

Change-Id: I74ea2e380d5ab9526ea1e6412929346ad9c0ead6
Reviewed-on: https://skia-review.googlesource.com/c/167921
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>