[Webkit-unassigned] [Bug 209565] New: Variable fonts with 'slnt' or 'ital' axes are not rendered correctly with font-style:italic, etc

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=209565

            Bug ID: 209565
           Summary: Variable fonts with 'slnt' or 'ital' axes are not
                    rendered correctly with font-style:italic, etc
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Text
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: stephen at arrowtype.com
                CC: mmaxfield at apple.com

Created attachment 394549

  --> https://bugs.webkit.org/attachment.cgi?id=394549&action=review

Screenshot of a test site for this issue

There is a collection of closely-related issues in the handling of variable fonts with either Slant (slnt) or Italic (ital) axes.

A test page detailing issues has been created here: https://arrowtype.github.io/vf-slnt-test/slnt-ital-tests/index.html

---

For fonts with a 'slnt' axis, issues include:

• font-style:italic; & font-style:oblique; & <i> doesn't activate max clockwise (negative) slant, but rather, synthesizes a slant

• font-style:oblique XXdeg; doesn't correctly flip the positive/negative value when requesting font slnt, so fonts that follow the OpenType spec (using negative values for clockwise slant) do not work correctly. Additionally, fonts with a positive,  a counter-clockwise "backslant" cannot be activated.


For fonts with an 'ital' axis, issues include:

• font-style:italic; or <i> will activate the ital axis, PLUS incorrectly add a synthesized extra 20 degrees of slant

• font-style:oblique; doesn't activate ital=1, but rather, synthesizes a slant

---

There are two semi-related issues, but the linked-to test page attempts to better capture the range of related problems.

• https://bugs.webkit.org/show_bug.cgi?id=200369, "Slanted text in variable fonts is not rendered correctly"

• and maybe https://bugs.webkit.org/show_bug.cgi?id=189483, "Fonts which understand the 'ital' axis get synthetic italics"

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