Fix scoped-VT auto-nesting [chromium/src : main]

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Kevin Ellis (Gerrit)

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Mar 5, 2026, 3:36:56 PM (yesterday) Mar 5
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Please take a look.

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Vladimir Levin (Gerrit)

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Mar 5, 2026, 3:38:33 PM (yesterday) Mar 5
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Vladimir Levin . resolved

Let's prioritize either always including transition_scoped.css or moving all of these rules to html.css, considering that we shouldn't be able to disable view transition (non-scoped) anymore

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    Blink W3C Test Autoroller (Gerrit)

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    Mar 5, 2026, 3:45:13 PM (yesterday) Mar 5
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    Message from Blink W3C Test Autoroller

    Exportable changes to web-platform-tests were detected in this CL and a pull request in the upstream repo has been made: https://github.com/web-platform-tests/wpt/pull/58299.

    When this CL lands, the bot will automatically merge the PR on GitHub if the required GitHub checks pass; otherwise, ecosystem-infra@ team will triage the failures and may contact you.

    WPT Export docs:
    https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md#Automatic-export-process

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    Steve Kobes (Gerrit)

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    Mar 5, 2026, 3:48:51 PM (yesterday) Mar 5
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    Vladimir Levin (Gerrit)

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    Mar 5, 2026, 6:00:34 PM (yesterday) Mar 5
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    Vladimir Levin added 1 comment

    File third_party/blink/web_tests/external/wpt/css/css-view-transitions/scoped/auto-nesting.html
    Line 9, Patchset 3 (Latest): <meta name="fuzzy" content="maxDifference=0-2; totalPixels=0-48600">
    Vladimir Levin . unresolved

    that's a lot of pixels... is this an animation that started running already and began a crossfade? if so, this is going to be flaky.

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      Kevin Ellis (Gerrit)

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      Kevin Ellis added 2 comments

      File third_party/blink/web_tests/external/wpt/css/css-view-transitions/scoped/auto-nesting.html
      Line 9, Patchset 3: <meta name="fuzzy" content="maxDifference=0-2; totalPixels=0-48600">
      Vladimir Levin . unresolved

      that's a lot of pixels... is this an animation that started running already and began a crossfade? if so, this is going to be flaky.

      Kevin Ellis

      Cross-fade has finished, however, pixels in final image could be from compositor or main thread. On other tests, we've noticed rounding errors. a maxDifference of 0-1 is likely fine, but wasn't sufficient on some wide-gamut tests. Though the number of pixels is high, the colors have to be very close. The pixel count and difference would be sell over the threshold if not properly clipped. Erring on the side of caution, against test flakes.

      Line 9, Patchset 3: <meta name="fuzzy" content="maxDifference=0-2; totalPixels=0-48600">
      Vladimir Levin . resolved

      that's a lot of pixels... is this an animation that started running already and began a crossfade? if so, this is going to be flaky.

      Kevin Ellis

      It's finished the crossfade. Don't require fuzzing when the test is run locally, but as we have seen rounding errors in other tests, decided to experiment here to determine if it resolved the problem.

      It turned out that the actual difference was significantly higher due to sub-pixel
      antialiasing, and rounding of the clip rect position. As the animation is paused at the finish line, I'm hopeful we have precise pixel values in the interior of each box, and that adding a margin to push painted pixels away from the border resolves the anti-aliasing issue.

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        Kevin Ellis (Gerrit)

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        1:36 PM (10 hours ago) 1:36 PM
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        Kevin Ellis . resolved

        Still wrestling with anti-aliasing artifacts.

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