musictheory/SwiffCore — Issue #7: ENH: Non-CG blend modes
Author: iccir
Created: 2012-01-01 03:27:18+00:00
State: open

The following blend mode don't have direct mappings to CGBlendModes:
Layer, Add, Subtract, Invert, Alpha, Erase

Add is close to kCGBlendModePlusLighter, but handles the alpha channel differently.
Invert is close to kCGBlendModeDifference, but draws using all black.

Erase and Alpha may have equivalent Porter-Duff modes.

See:
http://www.kaourantin.net/2005/09/some-word-on-blend-modes-in-flash.html