Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 689b91ff1913069d73cf1700b733c14e41e05c25
https://github.com/WebKit/WebKit/commit/689b91ff1913069d73cf1700b733c14e41e05c25
Author: Ahmad Saleem <[email protected]>
Date: 2026-06-26 (Fri, 26 Jun 2026)
Changed paths:
M
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-snap/snap-after-relayout/multiple-aligned-targets/prefer-targeted-element-expected.txt
M
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-snap/snap-after-relayout/multiple-aligned-targets/prefer-targeted-element-main-frame-expected.txt
M
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-snap/snap-after-relayout/multiple-aligned-targets/prefer-targeted-element-positioned-expected.txt
M LayoutTests/platform/mac/TestExpectations
M Source/WebCore/page/LocalFrameView.cpp
M Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.cpp
M Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.h
M Source/WebCore/platform/ScrollSnapAnimatorState.cpp
M Source/WebCore/rendering/RenderLayerScrollableArea.cpp
M Source/WebKit/Shared/WebCoreArgumentCoders.serialization.in
Log Message:
-----------
[CSS Scroll Snap] Re-snap does not prefer the focused or fragment-targeted
snap area among multiple aligned snap targets
https://bugs.webkit.org/show_bug.cgi?id=317481
rdar://180108825
Reviewed by Simon Fraser.
When several snap areas resolve to the same snap offset (an aligned "tie"), the
re-snap performed after a layout change must follow the highest-priority box per
https://drafts.csswg.org/css-scroll-snap-1/#re-snap: a focused box, then a
fragment-targeted (:target) box, then the box first in tree order.
WebCore only tracked focused boxes, and only re-chose a target when the tie
collapsed to a single box. So a fragment-targeted box was never preferred, and
when nothing was focused the choice fell back to an arbitrary hash-set order.
Track the document's fragment-targeted element through the snap-offset pipeline,
mirroring the existing focused-element handling:
- Add SnapOffset::isTarget, populated from Document::cssTarget(), and serialize
it so the async scrolling tree observes it as well.
- Accumulate isFocused/isTarget across every area that shares an offset (not
just the first one added), and point the offset's snapTargetID at the
highest-priority box (focused, then targeted, then first added) so re-snapping
resolves to it.
- During re-snap, when the scroller was snapped to multiple aligned boxes,
follow
a focused or targeted box to its post-layout offset even if other boxes remain
aligned at the old offset. With no such explicit preference, behavior is
unchanged: a target is only re-chosen once the tie collapses to a single box.
* LayoutTests/platform/mac/TestExpectations: Unskip now passing test
*
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-snap/snap-after-relayout/multiple-aligned-targets/prefer-targeted-element-expected.txt:
Progressions
*
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-snap/snap-after-relayout/multiple-aligned-targets/prefer-targeted-element-main-frame-expected.txt:
Ditto
*
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-snap/snap-after-relayout/multiple-aligned-targets/prefer-targeted-element-positioned-expected.txt:
Ditto
* Source/WebCore/page/LocalFrameView.cpp:
(WebCore::LocalFrameView::updateSnapOffsets): Pass the fragment-targeted element
* Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.cpp:
(WebCore::updateSnapOffsetsForScrollableArea): Accept the targeted element;
accumulate isFocused/isTarget and choose the representative snapTargetID,
preferring focused over targeted over the first box in tree order.
(WebCore::convertOffsetInfo):
* Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.h:
(WebCore::operator<<):
* Source/WebCore/platform/ScrollSnapAnimatorState.cpp:
(WebCore::ScrollSnapAnimatorState::preserveCurrentTargetForAxis):
(WebCore::preferredSnapTarget): Return the focused-then-targeted box, if any.
(WebCore::chooseBoxToResnapTo): Use preferredSnapTarget before the fallback.
(WebCore::ScrollSnapAnimatorState::resnapAfterLayout): Follow a preferred box
even while peers remain aligned.
* Source/WebCore/rendering/RenderLayerScrollableArea.cpp:
(WebCore::RenderLayerScrollableArea::updateSnapOffsets): Pass the
fragment-targeted element.
* Source/WebKit/Shared/WebCoreArgumentCoders.serialization.in:
Canonical link: https://commits.webkit.org/315880@main
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