Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: e1f2eaabdb5cd246aee4a328b8a81cbbe0043662
https://github.com/WebKit/WebKit/commit/e1f2eaabdb5cd246aee4a328b8a81cbbe0043662
Author: Simon Fraser <[email protected]>
Date: 2026-04-03 (Fri, 03 Apr 2026)
Changed paths:
A
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-disabled-above-threshold-expected.txt
A
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-disabled-above-threshold-in-overflow-expected.txt
A
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-disabled-above-threshold-in-overflow.html
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LayoutTests/fast/scrolling/scroll-anchoring/heuristic-disabled-above-threshold.html
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LayoutTests/fast/scrolling/scroll-anchoring/heuristic-enabled-below-threshold-expected.txt
A
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-enabled-below-threshold.html
A
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-enabled-large-cumulative-adjustment-expected.txt
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LayoutTests/fast/scrolling/scroll-anchoring/heuristic-enabled-large-cumulative-adjustment.html
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LayoutTests/fast/scrolling/scroll-anchoring/heuristic-renabled-after-delay-expected.txt
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LayoutTests/fast/scrolling/scroll-anchoring/heuristic-renabled-after-delay.html
A
LayoutTests/fast/scrolling/scroll-anchoring/resources/scroll-anchoring-utils.js
M LayoutTests/platform/ios/TestExpectations
M Source/WebCore/page/scrolling/ScrollAnchoringController.cpp
M Source/WebCore/page/scrolling/ScrollAnchoringController.h
Log Message:
-----------
[Scroll anchoring] Add a heuristic that disables scroll anchoring for
frequent adjustments
https://bugs.webkit.org/show_bug.cgi?id=311227
rdar://173680821
Reviewed by Abrar Rahman Protyasha.
Some sites (e.g. depop.com, linkedin.com) suffer from scroll position
oscillations triggered by scroll anchoring.
Such issues are easy to cause by accident by combining scroll position
observation (e.g. via window.scrollY
or Intersection Observer) and content changes. Gecko has a heuristic to disable
anchoring in cases like this,
so do something similar.
The goal here is to detect oscillations triggered by circular dependencies
between anchoring scrolls
and content changes, which will generally show up with a single frame delay,
but I allowed for about
two frames per update to account for slower web content, so I decided that 10
adjustments in 350ms
is the threshold above which anchoring will be temporarily disabled. It will
re-enable after 3s.
A user scroll will also re-enable it. The heuristic also computes the sum of
the cumulative adjustments,
looking for a small mean adjustment (since this indicates an oscillation
between two states).
webkit.org/b/311235 needs to be fixed before all the tests pass on iOS.
Tests: fast/scrolling/scroll-anchoring/heuristic-disabled-above-threshold.html
fast/scrolling/scroll-anchoring/heuristic-enabled-below-threshold.html
fast/scrolling/scroll-anchoring/heuristic-renabled-after-delay.html
*
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-disabled-above-threshold-expected.txt:
Added.
*
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-disabled-above-threshold-in-overflow-expected.txt:
Added.
*
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-disabled-above-threshold-in-overflow.html:
Added.
*
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-disabled-above-threshold.html:
Added.
*
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-enabled-below-threshold-expected.txt:
Added.
*
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-enabled-below-threshold.html:
Added.
*
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-enabled-large-cumulative-adjustment-expected.txt:
Added.
*
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-enabled-large-cumulative-adjustment.html:
Added.
*
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-renabled-after-delay-expected.txt:
Added.
*
LayoutTests/fast/scrolling/scroll-anchoring/heuristic-renabled-after-delay.html:
Added.
*
LayoutTests/fast/scrolling/scroll-anchoring/resources/scroll-anchoring-utils.js:
Added.
(toggleHeight):
* LayoutTests/platform/ios/TestExpectations:
* Source/WebCore/page/scrolling/ScrollAnchoringController.cpp:
(WebCore::ScrollAnchoringController::scrollPositionDidChange):
(WebCore::ScrollAnchoringController::adjustScrollPositionForAnchoring):
(WebCore::ScrollAnchoringController::DisablementHeuristic::disabledByHeuristic):
(WebCore::ScrollAnchoringController::DisablementHeuristic::reset):
* Source/WebCore/page/scrolling/ScrollAnchoringController.h:
Canonical link: https://commits.webkit.org/310545@main
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