Support for "plus-darker" in mix-blend-mode. Here is the email I sent to public-fx.
Our designers at Apple often request a blending operation that is not supported in the CSS Compositing and Blending specification: plus-darker. You can find many examples and discussion of this mode if you Bing on the Google.
We’d like to add this mode to Level 2.
Details are here: http://en.wikipedia.org/wiki/Blend_modes#Addition
The math is pretty simple:
R = min(0, (1 - D) + (1 - S))
(We should maybe consider adding plus-lighter as well, and subtractive modes based on designer feedback)
Created attachment 244946 [details]
Committed r178710: <http://trac.webkit.org/changeset/178710>