[Webkit-unassigned] [Bug 203768] New: Safari/WebKit not rendering glyph substitution (GSUB) correctly in variable fonts

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=203768

            Bug ID: 203768
           Summary: Safari/WebKit not rendering glyph substitution (GSUB)
                    correctly in variable fonts
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Text
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: arrowtypeco at gmail.com
                CC: mmaxfield at apple.com

Created attachment 382639

  --> https://bugs.webkit.org/attachment.cgi?id=382639&action=review

screenshot of website demonstrating Safari mishandling GSUB in variable font

Interactive HTML bug report: https://arrowtype.github.io/recursive/gsub-bug-and-hack_fix-safari/index.html

---

Summary:

Glyph substitution (GSUB) in variable fonts occurs when a character's shape is changed in a non-compatible way. Put simply, GSUB is when shape changes dramatically, rather than gradually, along an axis.

GSUB does work with multiple characters, BUT it fails if a string contains only one character.

This behavior is problematic for any websites that are demonstrating font design, or in any user-editable text field that may have 1 character at any given time, which may require GSUB to be activated to correct display.

As of Nov 1, 2019, this test fails in:

• Safari on macOS, Version 12.1.1 (14607.2.6.1.1)
• Safari Technology Preview, Release 95 (Safari 13.1, WebKit 14609.1.7)
• Safari in iOS 13.1.3

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