[Webkit-unassigned] [Bug 281739] New: Color bleeds out of Twemoji COLR Font when using skin tone variant

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=281739

            Bug ID: 281739
           Summary: Color bleeds out of Twemoji COLR Font when using skin
                    tone variant
           Product: WebKit
           Version: Safari 18
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Text
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: webkit.jiion at passinbox.com
                CC: fantasai.bugs at inkedblade.net, vitor.roriz at apple.com

Created attachment 472982

  --> https://bugs.webkit.org/attachment.cgi?id=472982&action=review

Video screenshot showing behaviour on text selection

When using Mozilla Twemoji COLR font (converted to .woff2, if that can change anything) to display a character emoji with a zero-width joiner and a skin tone variant, skin tone color bleeds out of emoji to cover surrounding text.

Selecting surrounding text makes selected text portion to its specified color, but not unselected text. I made a video capture to show behavior on text selection.

For what it worth, bug seems to affect Safari iOS 18.0.1 (but not 17.6.1), and Safari 18.0.1 on macOS Sonoma Version 14.7 — but not on Safari 18.0.1 on macOS Ventura 13.7.

Initial reduced test cases:
- reproducing bug with COLR Font: https://codepen.io/ffoodd/pen/Vwobpwq
- same example without COLR Font, no bug: https://codepen.io/ffoodd/pen/mdNmwVL

Extended test case by rik at webkit.org: https://codepen.io/Rik/pen/GRVmMRj

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