Bug 303217

Summary:

REGRESSION (289928@main): Svelte transition fade + transition scale results in flashing

Product:

WebKit

Reporter:

Paul Rhomberg <paulrhomberg01>

Component:

Animations

Assignee:

Nobody <webkit-unassigned>

Status:

RESOLVED FIXED

Severity:

Normal

CC:

bfulgham, graouts, graouts, ntim, simon.fraser, webkit-bug-importer, zalan

Priority:

Keywords:

InRadar, Regression

Version:

Safari 26

Hardware:

All

OS:

All

Attachments:

Description	Flags
Bug shows on iOS 26	none
No issues on Safari 18.x	none
Minimal svelte project	none

Paul Rhomberg

Reported 2025-11-27 15:59:25 PST

Created attachment 477539 [details] Bug shows on iOS 26 Hey, Please see the minimal attached svelte project. Install deps using `npm install`, then run using `npm run dev`, then click on the "Open Dialog" button. On Safari >=26.0, the dialog flashes. In Safari 18.x, no flashing appears. Firefox and Chrome also show the intended behavior. Please refer to the videos. Issue is prominent on both Mac, iOS and iPadOS.

Attachments
Bug shows on iOS 26 (4.09 MB, video/mp4) 2025-11-27 15:59 PST, Paul Rhomberg	no flags	Details
No issues on Safari 18.x (863.85 KB, video/quicktime) 2025-11-27 15:59 PST, Paul Rhomberg	no flags	Details
Minimal svelte project (28.86 KB, application/zip) 2025-11-27 16:00 PST, Paul Rhomberg	no flags	Details
View All Add attachment proposed patch, testcase, etc.

Paul Rhomberg

Comment 1 2025-11-27 15:59:49 PST

Created attachment 477540 [details] No issues on Safari 18.x

Paul Rhomberg

Comment 2 2025-11-27 16:00:51 PST

Created attachment 477541 [details] Minimal svelte project

Radar WebKit Bug Importer

Comment 3 2025-11-30 12:36:25 PST

<rdar://problem/165583864>

Simon Fraser (smfr)

Comment 4 2025-12-01 10:21:54 PST

Is the flashing you refer to exclusively in the Safari UI areas?

Paul Rhomberg

Comment 5 2025-12-01 10:56:36 PST

(In reply to Simon Fraser (smfr) from comment #4) > Is the flashing you refer to exclusively in the Safari UI areas? Hi, No, the safari UI areas are changing their color swiftly because the "main" color of the page changes due to the popup – that's not the "flashing" I mean. The flashing I'm referring to is the popup, after closing, flashes open for a short amount of time (see attached videos from the original report). This only happens in Safari 26.x and is related to the Popup's Svelte 5 "Scale" animation (see attached project).

Paul Rhomberg

Comment 6 2025-12-01 10:58:31 PST

(to be more specific – the background part of the popup flashes in again, not the white box that is scaling down)

Simon Fraser (smfr)

Comment 7 2025-12-01 11:01:44 PST

Got it, thanks for the clarification.

Simon Fraser (smfr)

Comment 8 2025-12-01 14:10:46 PST

Does this affect a deployed web site?

Tim Nguyen (:ntim)

Comment 9 2025-12-01 17:11:03 PST

I deployed the repro here to avoid a local setup: https://svelte.dev/playground/afe115a5b6d54810aec6d7d2bd95796d?version=latest

Simon Fraser (smfr)

Comment 10 2025-12-01 17:59:39 PST

Caused by 289928@main.

Nipun Shukla

Comment 11 2025-12-10 17:44:25 PST

Pull request: https://github.com/WebKit/WebKit/pull/55217

EWS

Comment 12 2025-12-18 14:51:02 PST

Committed 304710@main (42b3f8d91784): <https://commits.webkit.org/304710@main> Reviewed commits have been landed. Closing PR #55217 and removing active labels.

Paul Rhomberg

Comment 13 2025-12-18 15:10:51 PST

Thanks a ton for the quick fix!!

Note You need to log in before you can comment on or make changes to this bug.