On Tue, Nov 13, 2012 at 11:19 PM, Maciej Stachowiak <m...@apple.com> wrote:
> > On Nov 13, 2012, at 4:43 PM, Rik Cabanier <caban...@gmail.com> wrote: > > Maciej, > > did this sound reasonable to you? > > > Still doesn't make sense to me. Even if we don't implement CSS > 'alpha-compositing' and 'blend-mode' today, I assume we will want to > implement them eventually. At that point we will want them consistent with > Canvas. If the only reason to combine compositing operator and blend modes > is short-term ease of implementation on Mac, then that doesn't seem like a > great reason to make the Web platform permanently inconsistent. > > Would you object if Canvas combines blending and compositing but not CSS? > > > Yes. I think they should be consistent and the relevant standards group > (FX Task Force?) should decide. It's not even very important to me which is > chosen. It just seems arbitrary that they would make different choices on > this, especially when it is all defined in the same spec. > > Thanks Maciej! I will bring this up on the FX mailing list. Depending on the outcome, I will amend the compositing spec. > > 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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