Maciej, did this sound reasonable to you? Would you object if Canvas combines blending and compositing but not CSS?
Rik On Mon, Nov 12, 2012 at 3:46 PM, Rik Cabanier <caban...@gmail.com> wrote: > > > On Mon, Nov 12, 2012 at 12:14 PM, Maciej Stachowiak <m...@apple.com> wrote: > >> >> On Nov 11, 2012, at 9:06 PM, Rik Cabanier <caban...@gmail.com> wrote: >> >> >> >> On Sun, Nov 11, 2012 at 8:43 PM, Maciej Stachowiak <m...@apple.com> wrote: >> >>> >>> On Nov 11, 2012, at 6:59 PM, Rik Cabanier <caban...@gmail.com> wrote: >>> >>> >>> >>> >>>> >>>> Wouldn't it be better to add a new property to canvas for blending? At >>>> the beginning, implementations are just require to use different blend >>>> modes in combination with 'source-over'. >>> >>> >>> That could work too. >>> There was a mailing list conversation about this a couple of months ago, >>> and people were evenly split on the subject. >>> >>> The vast majority of cases will use 'source-over' in combination with >>> blending so maybe it's best to keep it simple... >>> >>> >>> It doesn't make sense to me for blend mode and composite operator to be >>> separate in CSS, but combined in Canvas. Either there are valid use cases >>> for specifying them separately or there are not. I cannot imagine how this >>> could differ between Canvas and CSS. >>> >>> There are cases where it makes sense to have them as separate properties. >> To be honest, the main reason that the Canvas proposal combines them, is >> because it is not possible to implement this efficiently using Core >> Graphics. >> >> If we break it up in 2 operations, we have to document the correct >> behavior (= blending does not force source-over for blending) because the >> spec can't be changed later. >> This means that Safari and Firefox for Mac can only implement part of the >> spec... >> >> I prefer to have a consistent implementation that can be extended later >> as opposed to a 'correct' API that is inconsistently implemented. >> >> >> Doesn't this same argument apply to CSS blend modes? (And therefore the >> 'blend-mode' and 'alpha-compositing' properties should be combined into a >> single property)? >> >> > Yes, except I'm not proposing that we implement the 'alpha-compositing' > property yet. > I hope that MacOS (or Safari) can evolve in the future so it can be > implemented more easily. > > Compositing in CSS is actually a much harder problem than in Canvas > because it requires the UA to keep track of the 'shape'. > >
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