[Webkit-unassigned] [Bug 130582] [CSS Blending]Wrong color result for basic blend modes
bugzilla-daemon at webkit.org
bugzilla-daemon at webkit.org
Fri Mar 21 05:34:41 PDT 2014
https://bugs.webkit.org/show_bug.cgi?id=130582
Mihai Tica <mitica at adobe.com> changed:
What |Removed |Added
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CC| |mitica at adobe.com
--- Comment #1 from Mihai Tica <mitica at adobe.com> 2014-03-21 05:35:03 PST ---
(In reply to comment #0)
> Created an attachment (id=227417)
--> (https://bugs.webkit.org/attachment.cgi?id=227417&action=review) [details]
> Sample for 'difference' mode results
>
> According to the spec[1], the 'difference' blend mode should be computed using this formula: B(Cb, Cs) = | Cb - Cs |.
> For example: Fuchsia difference Aqua = Yellow
>
> The result in webkit is different than Yellow. On retina display it's a pale yellow rgb(204, 214, 0), but on non-retina displays, the result is a pale green rgb(0, 190, 0).
>
> The behaviour is the same for both accelerated and non-accelerated blending. I did not test for other blend modes than difference (TBD).
>
> [1] http://dev.w3.org/fxtf/compositing-1/#blendingdifference
There are also problems with other blend modes. The biggest differences are with soft-light.
In fact, when validating canvas blend modes, the tests submitted https://bugs.webkit.org/show_bug.cgi?id=119082 entirely skip soft-light since the differences between the formula and the result are consistent.
Imho, this is rather a CG/CA bug.
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