Update: I changed the test substantially to make it more robust and avoid spurious fuzzy-failures, so the up-to-date WPT test linked in comment 0 isn't exercising this anymore. I landed a reftest with an expected-to-be-quite-fuzzy annotation that does continue to trigger this, though: https://searchfox.org/mozilla-central/source/layout/reftests/bugs/1841355-1.html That test is annotated as `fuzzy-if(!useDrawSnapshot&&!swgl,254-255,110-121)`, where the 254-to-255 color-channel-difference (under hardware WebRender) is due to this bug here. That test will help us validate whether this bug remains (since the test will start unexpectedly-passing if we improve); and hopefully someone can use that test as part of investigating tentative fixes here in the future.
Bug 1841355 Comment 1 Edit History
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Update: I changed the test substantially to make it more robust and avoid spurious fuzzy-failures, so the up-to-date WPT test linked in comment 0 isn't exercising this anymore. I landed a reftest with an expected-to-be-quite-fuzzy annotation that does continue to trigger this, though: https://searchfox.org/mozilla-central/source/layout/reftests/bugs/1841355-1.html That test is [annotated](https://searchfox.org/mozilla-central/rev/d35b3fe3d8230a255b988afb0ebda1176fc2f50b/layout/reftests/bugs/reftest.list#2160) as `fuzzy-if(!useDrawSnapshot&&!swgl,254-255,110-121)`, where the 254-to-255 color-channel-difference (under hardware WebRender) is due to this bug here. That test will help us validate whether this bug remains (since the test will start unexpectedly-passing if we improve); and hopefully someone can use that test as part of investigating tentative fixes here in the future.
Update: I changed the test substantially to make it more robust and avoid spurious fuzzy-failures, so the up-to-date WPT test linked in comment 0 isn't exercising this anymore. I [landed](https://hg.mozilla.org/mozilla-central/rev/409794f954d9) a reftest with an expected-to-be-quite-fuzzy annotation that does continue to trigger this, though: https://searchfox.org/mozilla-central/source/layout/reftests/bugs/1841355-1.html That test is [annotated](https://searchfox.org/mozilla-central/rev/d35b3fe3d8230a255b988afb0ebda1176fc2f50b/layout/reftests/bugs/reftest.list#2160) as `fuzzy-if(!useDrawSnapshot&&!swgl,254-255,110-121)`, where the 254-to-255 color-channel-difference (under hardware WebRender) is due to this bug here. That test will help us validate whether this bug remains (since the test will start unexpectedly-passing if we improve); and hopefully someone can use that test as part of investigating tentative fixes here in the future.