Bug 307966

Summary:

(Regression: Safari 26.x) Underline animation leaves traces (repaint issue)

Product:

WebKit

Reporter:

Ahmad Saleem <ahmad.saleem792>

Component:

Layout and Rendering

Assignee:

alan <zalan>

Status:

RESOLVED FIXED

Severity:

Normal

CC:

bfulgham, karlcow, simon.fraser, webkit-bug-importer, zalan

Priority:

Keywords:

BrowserCompat, InRadar

Version:

Safari Technology Preview

Hardware:

Unspecified

OS:

Unspecified

Attachments:

Description	Flags
STP237 - Video - Issue	none
Test reduction	none
[fast-cq]Patch	none

Ahmad Saleem

Reported 2026-02-15 20:11:08 PST

Hi Team, While going through article about macOS Tahoe window resize issue on blog, I noticed the bug and now filling here: **** Steps to Reproduce *** 1. Go to https://noheger.at/blog/about/ 2. Hover over `Launch Bar` or `Little Snitch` 3. It animates underline but some time leaves traces *** Actual Results *** It leaves traces, upon resize, it goes away - so repaint issue. *** Expected Result *** It should not leave traces. *** Regression Info *** It does not reproduces on Safari 26.3 but does on Safari Technology Preview 237. *** Other browsers *** Does not reproduce on Chrome Canary 147. Just raising, so we can fix it. Thanks!

Attachments
STP237 - Video - Issue (7.78 MB, video/quicktime) 2026-02-15 20:12 PST, Ahmad Saleem	no flags	Details
Test reduction (172.50 KB, text/html) 2026-02-16 10:49 PST, alan	no flags	Details
[fast-cq]Patch (3.60 KB, patch) 2026-02-16 18:20 PST, alan	no flags	Details Formatted Diff Diff
View All Add attachment proposed patch, testcase, etc.

Radar WebKit Bug Importer

Comment 1 2026-02-15 20:11:15 PST

<rdar://problem/170448325>

Ahmad Saleem

Comment 2 2026-02-15 20:12:33 PST

Created attachment 478368 [details] STP237 - Video - Issue

Ahmad Saleem

Comment 3 2026-02-15 20:13:47 PST

Good news - it is already fixed on WebKit ToT (Minibrowser - 307630@main).

alan

Comment 4 2026-02-16 10:49:55 PST

Created attachment 478377 [details] Test reduction This bug will come back with [subpixel inline layout]. It seems like we under-invalidate the area to repaint when content is on fractional pixel position.

alan

Comment 5 2026-02-16 18:20:03 PST

Created attachment 478380 [details] [fast-cq]Patch

EWS

Comment 6 2026-02-17 05:34:08 PST

Committed 307701@main (a349723e4b51): <https://commits.webkit.org/307701@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 478380 [details].

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