[Webkit-unassigned] [Bug 211625] New: Child elements stops displaying during some container transform transitions

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=211625

            Bug ID: 211625
           Summary: Child elements stops displaying during some container
                    transform transitions
           Product: WebKit
           Version: Safari 13
          Hardware: Macintosh
                OS: macOS 10.15
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: ian at ianbellomy.com

Created attachment 398861

  --> https://bugs.webkit.org/attachment.cgi?id=398861&action=review

Simplified example; Reproduce by repeatedly mashing keys 1,2,3 in very quick succession for a few moments.

Changes to element's transform (with transition) when start or end of transition includes scales > ~3 may lead to contained elements disappearing for duration of transition. Most often effects child SVGSVGElement, but have encountered it with child imgs. 

Can reliably induce the issue in the attached example after a few moments of repeatedly mashing keys 1,2,3 in very quick succession (not all at once). For a more complex setup in the wild but where the issue appears more consistently, go here: https://sheets.flechs.net/#Mad%20Cat%20Prime , and alternate between pressing "P" and "M" (or "S").

Doesn't reproduce in FF 75 (Mac); though in the same circumstances the transition freezes a moment then picks up towards the end.

Can reproduce in Chrome 81 (on Mac), though it _feels_ like it takes a little more to trigger the issue. 

Testing on a 15-inch 2017 MBP.

Issue also appears in mobile Safari under similar circumstances.

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