Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 000ed9be50923e8a72fc9f71f1682cdc2b528af9
https://github.com/WebKit/WebKit/commit/000ed9be50923e8a72fc9f71f1682cdc2b528af9
Author: Alan Baradlay <[email protected]>
Date: 2026-07-28 (Tue, 28 Jul 2026)
Changed paths:
M Source/WebCore/layout/formattingContexts/flex/FlexFormattingContext.cpp
M Source/WebCore/layout/formattingContexts/flex/FlexFormattingContext.h
Log Message:
-----------
[cleanup] Remove the column-reverse placement pass from the flex algorithm
https://bugs.webkit.org/show_bug.cgi?id=320394
Reviewed by Antti Koivisto.
layoutColumnReverse walked each line a second time after placeFlexItems had
already placed it,
subtracting where the first walk added, to lay the items out from the
container's main-axis end. Two
placement functions had to stay in step, and column-reverse was the last
flex-direction reversal the
algorithm resolved while laying out rather than at the
flow-relative-to-physical conversion.
computeFlexItemRects can flip the positions instead, now that it runs after the
container's block extent
is final -- which is what the second pass was waiting for. It flips the item's
*margin* box and steps back
over its leading margin: the two walks consume marginStart and marginEnd in
opposite orders, so flipping
the border box only lines up if those two swap, while the margin box is
symmetric under reversal by
construction.
The edge to flip about is the container's main border-box extent, less the
main-axis scrollbar, adjusted
by the difference between the flow-aware start and end border+padding -- the
same quantities the removed
walk started from.
Note this flip keys off flex-direction alone and leaves isLeftToRightFlow
untouched. For a column the
writing mode's own reversal is already accounted for twice over:
isLeftToRightFlow moves the flow-aware
start edge, and the renderer flips the position in
RenderBox::flipForWritingMode, since RenderBox::location
is stored in flipped-blocks coordinates. Folding flex-direction into
isLeftToRightFlow would reverse a
vertical-rl column twice and leave vertical-rl column-reverse unreversed.
With this, every reversed direction -- row-reverse, RTL rows, column-reverse,
wrap-reverse and rtl-column
-- is resolved in computeFlexItemRects, and the algorithm above it lays every
line out forwards.
No change in behaviour.
* Source/WebCore/layout/formattingContexts/flex/FlexFormattingContext.cpp:
(WebCore::FlexFormattingContext::layout):
(WebCore::FlexFormattingContext::computeFlexItemRects):
(WebCore::FlexFormattingContext::reverseColumnLinesFromContainerMainEndIfNeeded):
Deleted.
(WebCore::FlexFormattingContext::layoutColumnReverse): Deleted.
* Source/WebCore/layout/formattingContexts/flex/FlexFormattingContext.h:
Canonical link: https://commits.webkit.org/318079@main
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