[Webkit-unassigned] [Bug 283709] New: Content shift happening while a View Transition runs inside an iframe

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=283709

            Bug ID: 283709
           Summary: Content shift happening while a View Transition runs
                    inside an iframe
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Mac (Apple Silicon)
                OS: macOS 15
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: New Bugs
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: bramus at google.com

Created attachment 473373

  --> https://bugs.webkit.org/attachment.cgi?id=473373&action=review

Screen Recording

1. Visit https://www.bram.us/2024/11/25/experiment-automatically-triggered-view-transitions-with-mutationobserver/#shortcomings
2. Click on the of the lime/hotpink/grey boxes in the embedded demo

While the View Transition runs, the entire CodePen embed’s content gets shifted by a pixel. Not sure what is causing this, but it is happening.

Note that the View Transition is actually running inside a nested iframe: you have the CodePen embed (which is an iframe) that contains the CodePen UI + the demo (which itself is also in an iframe). It is the outer iframe that is shifting, not just the demo one.

See attached screen recording.

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