Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: f9b924f3b1181c07bab2e627ef738777efa791e0
https://github.com/WebKit/WebKit/commit/f9b924f3b1181c07bab2e627ef738777efa791e0
Author: Charlie Wolfe <[email protected]>
Date: 2026-06-16 (Tue, 16 Jun 2026)
Changed paths:
A
LayoutTests/imported/w3c/web-platform-tests/css/css-transforms/animation/transform-interpolation-rotate3d-180deg-near-x-axis-expected.txt
A
LayoutTests/imported/w3c/web-platform-tests/css/css-transforms/animation/transform-interpolation-rotate3d-180deg-near-x-axis.html
M Source/WebCore/platform/graphics/transforms/TransformationMatrix.cpp
Log Message:
-----------
decompose4() computes the wrong quaternion y component
https://bugs.webkit.org/show_bug.cgi?id=316896
rdar://179334309
Reviewed by Simon Fraser.
When the matrix's X diagonal element is largest, decompose4() knows x and uses
s = 1 / (4 * x) to
recover the other quaternion components.
CSS Transforms Level 2 defines the relevant rotation matrix entries as
2 * (x * y - z * w) and 2 * (x * y + z * w):
https://www.w3.org/TR/css-transforms-2/#recomposing-to-a-3d-matrix
These entries must be added to recover y, since their sum is 4 * x * y.
Subtracting them cancels the
xy term and yields the wrong rotation axis for matrices near a 180° rotation
whose largest axis
component is X.
Test:
imported/w3c/web-platform-tests/css/css-transforms/animation/transform-interpolation-rotate3d-180deg-near-x-axis.html
*
LayoutTests/imported/w3c/web-platform-tests/css/css-transforms/animation/transform-interpolation-rotate3d-180deg-near-x-axis-expected.txt:
Added.
*
LayoutTests/imported/w3c/web-platform-tests/css/css-transforms/animation/transform-interpolation-rotate3d-180deg-near-x-axis.html:
Added.
* Source/WebCore/platform/graphics/transforms/TransformationMatrix.cpp:
(WebCore::decompose4):
Canonical link: https://commits.webkit.org/315288@main
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