Issue 14627 in skia: CPU Backend: Color filter applied to opaque shader with paint alpha is incorrect
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brian… via monorail
Jul 18, 2023, 11:42:31 AM7/18/23
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Status: Accepted
Owner: brian...@google.com
Priority: Medium
Type: Defect
New issue 14627 by brian...@google.com: CPU Backend: Color filter applied to opaque shader with paint alpha is incorrect
https://bugs.chromium.org/p/skia/issues/detail?id=14627
Trivial repro case: https://fiddle.skia.org/c/cf5ba8db0127c238e362348100869935
This is a bug in SkColorFilterShader, which is used to simplify the paint for the CPU backend. That class turns the color filter into a wrapper shader that invokes the original paint shader, then applies paint alpha, and then invokes the color filter. However, when it calls the color filter, the argument for 'shaderIsOpaque' is only determined by the shader, not the paint alpha. This means that with an opaque shader, paint alpha, and a color filter, the color filter gets an incorrect value for shaderIsOpaque. Many (most) color filters operate on unpremul colors, and use that bool to skip doing an unpremul/premul pair - producing different results.
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Owner: brian...@google.com
Priority: Medium
Type: Defect
New issue 14627 by brian...@google.com: CPU Backend: Color filter applied to opaque shader with paint alpha is incorrect
https://bugs.chromium.org/p/skia/issues/detail?id=14627
Trivial repro case: https://fiddle.skia.org/c/cf5ba8db0127c238e362348100869935
This is a bug in SkColorFilterShader, which is used to simplify the paint for the CPU backend. That class turns the color filter into a wrapper shader that invokes the original paint shader, then applies paint alpha, and then invokes the color filter. However, when it calls the color filter, the argument for 'shaderIsOpaque' is only determined by the shader, not the paint alpha. This means that with an opaque shader, paint alpha, and a color filter, the color filter gets an incorrect value for shaderIsOpaque. Many (most) color filters operate on unpremul colors, and use that bool to skip doing an unpremul/premul pair - producing different results.
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Git Watcher via monorail
Jul 18, 2023, 1:06:27 PM7/18/23
to bu...@skia.org
Comment #1 on issue 14627 by Git Watcher: CPU Backend: Color filter applied to opaque shader with paint alpha is incorrect
https://bugs.chromium.org/p/skia/issues/detail?id=14627#c1
The following revision refers to this bug:
https://skia.googlesource.com/skia/+/4e518e65fea051eb148e8078bfce88c72aeb6c6d
commit 4e518e65fea051eb148e8078bfce88c72aeb6c6d
Author: Brian Osman <brian...@google.com>
Date: Tue Jul 18 15:48:52 2023
CPU backend: Don't ignore paint alpha with opaque shader + color filter
Bug: skia:14627
Change-Id: I34391f789e59edff01253e0853b820ceb6a306bf
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/725696
Reviewed-by: John Stiles <johns...@google.com>
Commit-Queue: Brian Osman <brian...@google.com>
[modify] https://crrev.com/4e518e65fea051eb148e8078bfce88c72aeb6c6d/src/shaders/SkColorFilterShader.cpp
[modify] https://crrev.com/4e518e65fea051eb148e8078bfce88c72aeb6c6d/gm/colorfilters.cpp
brian… via monorail
Jul 18, 2023, 1:06:56 PM7/18/23
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Updates:
Status: Fixed
Comment #2 on issue 14627 by brian...@google.com: CPU Backend: Color filter applied to opaque shader with paint alpha is incorrect
https://bugs.chromium.org/p/skia/issues/detail?id=14627#c2
(No comment was entered for this change.)
Status: Fixed
Comment #2 on issue 14627 by brian...@google.com: CPU Backend: Color filter applied to opaque shader with paint alpha is incorrect
https://bugs.chromium.org/p/skia/issues/detail?id=14627#c2
(No comment was entered for this change.)
Git Watcher via monorail
Jul 20, 2023, 3:57:07 PM7/20/23
to bu...@skia.org
Comment #3 on issue 14627 by Git Watcher: CPU Backend: Color filter applied to opaque shader with paint alpha is incorrect
https://bugs.chromium.org/p/skia/issues/detail?id=14627#c3
The following revision refers to this bug:
https://skia.googlesource.com/skia/+/303245328527a281a603fa92acceb78d620efdb9
commit 303245328527a281a603fa92acceb78d620efdb9
Author: Brian Osman <brian...@google.com>
Date: Thu Jul 20 18:15:39 2023
Convert recently added GM to unit test
Bug: skia:14627
Change-Id: Ia0c199bca345d92cb0318426216877f9242c2050
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/727078
Reviewed-by: Robert Phillips <robertp...@google.com>
Commit-Queue: Brian Osman <brian...@google.com>
[modify] https://crrev.com/303245328527a281a603fa92acceb78d620efdb9/gm/colorfilters.cpp
[modify] https://crrev.com/303245328527a281a603fa92acceb78d620efdb9/tests/ColorFilterTest.cpp
commit 303245328527a281a603fa92acceb78d620efdb9
Author: Brian Osman <brian...@google.com>
Date: Thu Jul 20 18:15:39 2023
Convert recently added GM to unit test
Bug: skia:14627
Change-Id: Ia0c199bca345d92cb0318426216877f9242c2050
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/727078
Reviewed-by: Robert Phillips <robertp...@google.com>
Commit-Queue: Brian Osman <brian...@google.com>
[modify] https://crrev.com/303245328527a281a603fa92acceb78d620efdb9/gm/colorfilters.cpp
[modify] https://crrev.com/303245328527a281a603fa92acceb78d620efdb9/tests/ColorFilterTest.cpp
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