[Webkit-unassigned] [Bug 257746] New: Text opacity shows glyph overlap for cursive scripts

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=257746

            Bug ID: 257746
           Summary: Text opacity shows glyph overlap for cursive scripts
           Product: WebKit
           Version: Safari 16
          Hardware: Unspecified
                OS: macOS 12
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Text
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: ishida at w3.org
                CC: mmaxfield at apple.com

Created attachment 466603

  --> https://bugs.webkit.org/attachment.cgi?id=466603&action=review

N'Ko text showing no overlaps in opaque cursive text

This issue is likely to apply to all cursive script text.

Text in 'cursive' writing systems is joined by overlapping glyphs with the appropriate joining forms. If those glyphs are made opaque, the joins should not become apparent. For example, N'Ko should look like shown in the attached image.

css-color was updated to clarify that opacity should be applied to a whole element, not to individual letters, so that this shouldn't happen.

WebKit works as expected for Arabic, Devanagari, Syriac & N'Ko, but not for Adlam (Fulah), Mongolian, or Hanifi Rohingya.

It seems that a fix has been applied for certain scripts, but needs to be extended for those mentioned (plus Mandaic).



Tests

Interactive test, Applying opacity to cursive text doesn't produce dark patches where glyphs overlap
https://github.com/w3c/character_phrase_tests/issues/40


I18n test suite, Text opacity
https://w3c.github.io/i18n-tests/results/cursive#text_opacity

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