Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: ab284b2b78794e09d0d9250ed336cc01cd4e8b34
https://github.com/WebKit/WebKit/commit/ab284b2b78794e09d0d9250ed336cc01cd4e8b34
Author: Wenson Hsieh <[email protected]>
Date: 2025-10-15 (Wed, 15 Oct 2025)
Changed paths:
A
LayoutTests/fast/page-color-sampling/color-sampling-skips-negative-z-index-modal-containers-expected.txt
A
LayoutTests/fast/page-color-sampling/color-sampling-skips-negative-z-index-modal-containers.html
M Source/WebCore/page/LocalFrameView.cpp
Log Message:
-----------
REGRESSION (298506@main): [PLT6] ~13% increase in time to first paint /
DOMContentLoaded on Facebook
https://bugs.webkit.org/show_bug.cgi?id=300831
rdar://162552413
Reviewed by Abrar Rahman Protyasha.
After the changes in 298506@main, we now get a bottom fixed color extension on
the old, PLT 6
version of Twitter (notably, not Facebook) due to the fact that we no longer
ignore viewport-sized
modal containers for the purposes of color sampling. This means that when
navigating from Twitter to
Facebook during warm PLT 6 (these two subtests run back-to-back), Safari
removes the solid color
extension behind the navigation bar, which causes UIKit's scroll pocket code to
resample and re-
render the scroll pocket.
This additional spike in CPU / GPU activity during navigation subsequently
slows down the time to
first paint on Facebook by a few milliseconds — enough to cause a significant
regression on certain
(older) device models.
To mitigate this, we make some changes to the color sampling heuristic, such
that we avoid detecting
the fixed-position container (which is z-ordered below the rest of the feed) on
Twitter for the
purposes of color sampling.
Test:
fast/page-color-sampling/color-sampling-skips-negative-z-index-modal-containers.html
*
LayoutTests/fast/page-color-sampling/color-sampling-skips-negative-z-index-modal-containers-expected.txt:
Added.
*
LayoutTests/fast/page-color-sampling/color-sampling-skips-negative-z-index-modal-containers.html:
Added.
Add a new layout test to exercise this adjustment.
* Source/WebCore/page/LocalFrameView.cpp:
(WebCore::LocalFrameView::fixedContainerEdges const):
Don't consider large (viewport-sized) containers with a negative `z-index` as
candidates for color
sampling.
Canonical link: https://commits.webkit.org/301605@main
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