[whatwg] Canvas: clarification of compositing operations needed
david at davidflanagan.com
Wed Jul 28 14:43:12 PDT 2010
Firefox and Chrome disagree about the implementation of the
destination-atop, source-in, destination-in, and source-out compositing
operators. Test code is attached.
Chrome doesn't touch any destination pixels that are not underneath the
source pixels. Firefox, on the other hand, treats the entire canvas
(inside the clipping region) as the destination and if you use the
destination-in operator, for example, will erase any pixels outside of
whatever you are drawing.
I suspect, based on the reference to an "infinite transparent black
bitmap" in 220.127.116.11.13 Drawing model that Firefox gets this right and
Chrome gets it wrong, but it would be nice to have that confirmed.
I suggest clarifying 18.104.22.168.3 Compositing to mention that the
compositing operation takes place on all pixels within the clipping
region, and that some compositing operators clear large portions of the
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