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Opacity group compositing treats premultiplied RGBA as unpremultiplied RGBA #1449

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mstange opened this issue Jul 1, 2017 · 5 comments
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Opacity group compositing treats premultiplied RGBA as unpremultiplied RGBA #1449

mstange opened this issue Jul 1, 2017 · 5 comments
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@kvark
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type: bug

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@mstange
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@mstange mstange commented Jul 1, 2017 •
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Testcase: testcase
Screenshot:
screen shot 2017-07-01 at 2 35 25 pm
Firefox left, Servo right.

This box has a greyish fill in both servo and webrendest Gecko. It should have a yellow-whitish fill.
@kvark kvark added the type: bug label Jul 4, 2017
@mrobinson
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@mrobinson mrobinson commented Jul 12, 2017

Is this a duplicate of #1354?
@mstange
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@mstange mstange commented Jul 13, 2017

Looks like it, yes.
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@kvark kvark commented Jul 17, 2017

It appears to not be the issue about color pre-multiplication. The problem lies within blend modes we use for opacity, and the fact our cache target is cleared with black. So, having 2 opacity filters means one has to go through the cache target, and thus gets blended with black color, which screws up the result.
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@kvark kvark commented Jul 17, 2017

@glennw I think, internally, our task API should have the (optional) clear color information. The renderer will then make sure that the task gets proper background color.
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@kvark kvark commented Jul 17, 2017 •
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Edit: my previous 2 comments were related to #1354, not this one.
Edit2: actually, disregard these comments.
@kvark kvark self-assigned this Jul 17, 2017
@kvark kvark mentioned this issue Jul 18, 2017
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bors-servo added a commit that referenced this issue Jul 19, 2017
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Auto merge of #1493 - kvark:opacity, r=glennw,rhunt
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831b1e9 
Pre-multiplied alpha for the blend pass

Fixes #1449, fixes #1354
Running Servo tests is pending... Done.

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Pre-multiplied alpha for the blend pass
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@mrobinson @kvark @mstange
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