[Webkit-unassigned] [Bug 48297] Fix LayoutTests/canvas/philip/tests/2d.composite.uncovered.image.destination-atop.html

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=48297





--- Comment #9 from Mustafizur Rahaman <mustaf.here at gmail.com>  2011-06-07 12:01:34 PST ---
(In reply to comment #8)
> (In reply to comment #3)
> > (From update of attachment 95887 [details] [details])
> > View in context: https://bugs.webkit.org/attachment.cgi?id=95887&action=review
> > 
> > > Source/WebCore/html/canvas/CanvasRenderingContext2D.cpp:1513
> > >      // CompositeSourceAtop is not listed here as the platforms already implement the specification's behavior.
> > 
> > This comment no longer makes sense.
> 
> I disagree, it still makes sense. CompositeSourceAtop is marked as needed transparency everywhere else in the spec. However the platforms already implement the right behavior, thus there is no need to re-do the work here.
> 
> I am quite concerned with having different behaviors for source-atop vs destination-atop. If your testing shows that this change is needed, I would rather remove the comment and make sure both work the same.

I have used the same test case LayoutTests/canvas/philip/tests/2d.composite.uncovered.image.destination-atop.html & modified it to source-atop(changed only this line ctx.globalCompositeOperation = 'source-atop';). 

When I verified this behavior in both FF & Safari, the source-atop & destination-atop behaviors were different & as per my understanding from the spec for these two test cases, the behaviors should be different.
> 
> Also if you change the behavior for source-atop, shouldn't fast/canvas/canvas-composite-alpha.html need a rebaseline too?

So, without my changes, source-atop works the same way in Safari, FF & Opera, i.e. no code changes required. In my opinion, we should only fix the destination-atop issue for WebKit code.

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