Bug 307949

Summary: Rotating bounding box invalidation does not redraw a border on other element
Product: WebKit Reporter: Jonathan Deutsch <jonathan>
Component: Layout and RenderingAssignee: Nobody <webkit-unassigned>
Status: RESOLVED FIXED    
Severity: Major CC: ahmad.saleem792, bfulgham, jonathan, simon.fraser, webkit-bug-importer, zalan
Priority: P2 Keywords: BrowserCompat, InRadar
Version: Safari Technology Preview   
Hardware: Mac (Apple Silicon)   
OS: macOS 26   
Attachments:
Description Flags
Reproduction HTML Document
none
Screenshot of the bug in Safari
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Video showing Chrome (left) vs Safari with bug (right) none

Jonathan Deutsch
Reported 2026-02-15 12:41:05 PST
Created attachment 478358 [details] Reproduction HTML Document A div that has rotates can cause a region to be invalidated for repainting. However, if there's another element underneath that has a border, this border may not be repainted. Please see the simple repro case html document and video (Safari vs Chrome). The issue can be reproduced on: macOS 15.7.4 (24G517) and Safari Version 26.3 (20623.2.7.18.1) macOS 15.7.4 (24G517) and Safari Technology Preview Release 237 (WebKit 20625.1.3.19.2) macOS 26.1 Beta (25B5042k) and Safari Version 26.1 (21622.2.5) The issue does not reproduce on: macOS 14.4 (23E214) and Safari Version 17.4 (19618.1.15.11.12) Chrome Firefox WKWebView inside of a native mac app on macOS 15.7.4 This bug affects users of the Tumult Hype application for macOS: https://tumult.com/hype/
Attachments
Reproduction HTML Document (1.48 KB, text/html)
2026-02-15 12:41 PST, Jonathan Deutsch 		no flags
Details
Screenshot of the bug in Safari (34.18 KB, image/png)
2026-02-15 12:42 PST, Jonathan Deutsch 		no flags
Details
Video showing Chrome (left) vs Safari with bug (right) (1.73 MB, video/quicktime)
2026-02-15 12:43 PST, Jonathan Deutsch 		no flags
Details
View All Add attachment proposed patch, testcase, etc.
Jonathan Deutsch
Comment 1 2026-02-15 12:42:47 PST
Created attachment 478359 [details] Screenshot of the bug in Safari
Jonathan Deutsch
Comment 2 2026-02-15 12:43:21 PST
Created attachment 478360 [details] Video showing Chrome (left) vs Safari with bug (right)
Jonathan Deutsch
Comment 3 2026-02-15 12:50:08 PST
Note that adding `will-change: transform;` to the #small-box CSS will workaround the issue.
Radar WebKit Bug Importer
Comment 4 2026-02-15 14:09:20 PST
<rdar://problem/170438404>
Ahmad Saleem
Comment 5 2026-02-15 14:09:51 PST
I am able to reproduce on WebKit ToT (Minibrowser - 307621@main).
Ahmad Saleem
Comment 6 2026-02-15 14:12:21 PST
*** Chrome Canary 147 (147.0.7688.0 (Official Build) canary (arm64) ) *** Does not reproduce. *** Fireofx Nightly 149 (20260215090851) *** Does not reproduce.
Simon Fraser (smfr)
Comment 7 2026-02-16 10:06:55 PST
This is a repaint bug.
Nipun Shukla
Comment 8 2026-02-19 17:45:15 PST
Pull request: https://github.com/WebKit/WebKit/pull/59049
EWS
Comment 9 2026-02-20 11:20:13 PST
Committed 307930@main (54b6555c4fa6): <https://commits.webkit.org/307930@main> Reviewed commits have been landed. Closing PR #59049 and removing active labels.
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