Bug 303217 – REGRESSION (289928@main): Svelte transition fade + transition scale results in flashing

• Status: RESOLVED
• Resolution: FIXED
• Component: Animations

[Paul Rhomberg]

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.

[Paul Rhomberg]

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

[Paul Rhomberg]

Created attachment 477541 [details]
Minimal svelte project

[Radar WebKit Bug Importer]

<rdar://problem/165583864>

[Simon Fraser (smfr)]

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

[Paul Rhomberg]

(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]

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

[Simon Fraser (smfr)]

Got it, thanks for the clarification.

[Simon Fraser (smfr)]

Does this affect a deployed web site?

[Tim Nguyen (:ntim)]

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

[Simon Fraser (smfr)]

Caused by 289928@main.

[Nipun Shukla]

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

[EWS]

Committed 304710@main (42b3f8d91784): <https://commits.webkit.org/304710@main>

Reviewed commits have been landed. Closing PR #55217 and removing active labels.

[Paul Rhomberg]

Thanks a ton for the quick fix!!