Premultiplied alpha blend state instead of math

jpark37 commented 2 years ago

Description

This is an attempt to preserve RGB channels to behave like Chrome. This should work on a black background, but blending against anything else will be done in linear space, and may not look as expected.

Requires obsproject/obs-studio#5354

Motivation and Context

People want semi-transparency to work as expected.

How Has This Been Tested?

WebM video supplied by #5347 seems to look like Chrome in browser source with or without default custom CSS.

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist:

[x] My code has been run through clang-format.
[x] I have read the contributing document.
[x] My code is not on the master branch.
[x] The code has been tested.
[x] All commit messages are properly formatted and commits squashed where appropriate.
[x] I have included updates to all appropriate documentation.

jpark37 commented 2 years ago

In draft mode until required PR is merged.

jpark37 commented 2 years ago

Seems to work as I expect on Windows, Ubuntu, and macOS (with and without browserhwaccel).

obsproject / obs-browser