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Use border box or layout overflow rect for layout shift tracking #24762

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merged 1 commit into from Aug 1, 2020

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@chromium-wpt-export-bot chromium-wpt-export-bot commented Jul 27, 2020

This CL addresses the following issues of layout shift tracking:

  • Changed visual overflows triggered layout shift report
    (originally filed as crbug.com/1090763).
  • Descendant layout overflows were not included in ancestor's layout
    shift report.
  • Unnecessary descendant layout shift report.
  • Slow visual rect calculation for LayoutInline and LayoutText.

It includes the following changes

  • Track LayoutBoxes and LayoutTexts only.
  • Track both old and new starting points and visual representations
    instead of using location of visual rects as starting points.
  • For a LayoutBox, the local visual representation is the layout
    overflow rect if the LayoutBox has layout overflow and doesn't clip
    overflow. Otherwise use the border box rect.
  • For a LayoutText, suppose its shift causes shift of all contents
    in containing block logically below the LayoutText, and use that
    part of visual representation of the containing block as the visual
    representation of the shift.
  • Map both local starting points and local visual representations to
    the initial containing block and viewport.

This has the following benefits:

  • More accurate starting points and visual representations, conforming
    to the specs;
  • Better performance by
    • avoiding unnecessary layout shift reports of descendants
    • avoiding slow LayoutInline and LayoutText visual rect calculation.
  • sizeof(LayoutObject) is reduced by 16 bytes because now we use the
    previous geometry data in LayoutBoxes for paint invalidation.

Bug: 1108622
Change-Id: I7ebb4e250e7ca2a03b4dadea50034e300e55ad84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2319538
Reviewed-by: Steve Kobes <skobes@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793806}

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The review process for this patch is being conducted in the Chromium project.

@chromium-wpt-export-bot chromium-wpt-export-bot force-pushed the chromium-export-cl-2319538 branch from f7d27ab to f3e8996 Jul 29, 2020
@chromium-wpt-export-bot chromium-wpt-export-bot changed the title Use border box rect for layout shift tracking Use border box or layout overflow rect for layout shift tracking Jul 29, 2020
@chromium-wpt-export-bot chromium-wpt-export-bot force-pushed the chromium-export-cl-2319538 branch 7 times, most recently from a2ff6a8 to a815dca Jul 29, 2020
This CL addresses the following issues of layout shift tracking:
- Changed visual overflows triggered layout shift report
  (originally filed as crbug.com/1090763).
- Descendant layout overflows were not included in ancestor's layout
  shift report.
- Unnecessary descendant layout shift report.
- Slow visual rect calculation for LayoutInline and LayoutText.

It includes the following changes
- Track LayoutBoxes and LayoutTexts only.
- Track both old and new starting points and visual representations
  instead of using location of visual rects as starting points.
- For a LayoutBox, the local visual representation is the layout
  overflow rect if the LayoutBox has layout overflow and doesn't clip
  overflow. Otherwise use the border box rect.
- For a LayoutText, suppose its shift causes shift of all contents
  in containing block logically below the LayoutText, and use that
  part of visual representation of the containing block as the visual
  representation of the shift.
- Map both local starting points and local visual representations to
  the initial containing block and viewport.

This has the following benefits:
- More accurate starting points and visual representations, conforming
  to the specs;
- Better performance by
  * avoiding unnecessary layout shift reports of descendants
  * avoiding slow LayoutInline and LayoutText visual rect calculation.
- sizeof(LayoutObject) is reduced by 16 bytes because now we use the
  previous geometry data in LayoutBoxes for paint invalidation.

Bug: 1108622
Change-Id: I7ebb4e250e7ca2a03b4dadea50034e300e55ad84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2319538
Reviewed-by: Steve Kobes <skobes@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793806}
@chromium-wpt-export-bot chromium-wpt-export-bot force-pushed the chromium-export-cl-2319538 branch from a815dca to e0858e8 Jul 31, 2020
@chromium-wpt-export-bot chromium-wpt-export-bot merged commit 0f1dddc into master Aug 1, 2020
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@chromium-wpt-export-bot chromium-wpt-export-bot deleted the chromium-export-cl-2319538 branch Aug 1, 2020
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3 participants