Bug 308658 – [iOS] compositing/geometry/fixed-position-composited-page-scale-smaller-than-viewport.html is a flaky image diff

• Component: New Bugs
• Status: NEW

[Diego De La Toba]

compositing/geometry/fixed-position-composited-page-scale-smaller-than-viewport.html is a flaky image diff on iOS 26.2


HISTORY:
https://results.webkit.org/?suite=layout-tests&test=compositing%2Fgeometry%2Ffixed-position-composited-page-scale-smaller-than-viewport.html


IMAGE URL:
https://build.webkit.org/results/Apple-iOS-26-Simulator-Release-WK2-Tests/308176%40main%20(1896)/compositing/geometry/fixed-position-composited-page-scale-smaller-than-viewport-diffs.html


IMAGES:
See attached.


REPRODUCITON:
I was able to reliably reproduce this failure on iOS 26.2 release ToT with the following:

run-webkit-tests --no-build --no-retry --no-show-results --exit-after-n-failures=1 --expect-pass --iterations=1000 --force -f --ios-simulator --release compositing/geometry/fixed-position-composited-page-scale-smaller-than-viewport.html --udid < 3 devices >

Note: While the command above reliably reproduces the failure, it does still reproduce less often without running fully parallel.

I am going to mark expectations as pass imageOnlyFailure while this pends investigation

[Radar WebKit Bug Importer]

<rdar://problem/171189471>

[Diego De La Toba]

Created attachment 478477 [details]
image diffs

[Diego De La Toba]

Pull request: https://github.com/WebKit/WebKit/pull/59436

[EWS]

Test gardening commit 308221@main (afbcd0a20b24): <https://commits.webkit.org/308221@main>

Reviewed commits have been landed. Closing PR #59436 and removing active labels.

[Diego De La Toba]

Looking at the image expected vs actual I am seeing failures when the text is rendering with subtle subpixel antialiasing differences between runs, causing image comparison failures. However, there are no diffs in what the text is actually testing.  Removing the text resolves the issue but this could point to an issue with WebKit's rendering? Regardless putting up a PR with this patch since it seems like a viable option to resolve the flake considering the text is arbitrary. 

Note: Attempted to fix the antialiasing with -webkit-font-smoothing: none and text-rendering: geometricPrecision but neither resolved the inconsistent text rendering on iOS. Removing the text is the most reliable fix.

[Diego De La Toba]

Pull request: https://github.com/WebKit/WebKit/pull/59442