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Re: [csswg-drafts] [css-fonts-4] [varfont] Italic & Oblique benefit from not including a <number>

From: Peter Constable via GitHub <sysbot+gh@w3.org>
Date: Tue, 03 Jul 2018 05:30:57 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-402017709-1530595856-sysbot+gh@w3.org>
If a number is provided and it's a variable font with a slnt axis, then the UA can provide that angle --- or the min/max if beyond the axis range of the font.

If a number is provided and it's _not_ a variable font, then the UA could select an oblique font from the family, if present, even if the angle isn't exactly as specified. (Btw, the italicAngle field in the 'post' table is meant to indicate what the angle is of a static oblique/italic font.) Or, hypothetically, the UA synthetically slant the Regular from that family (if present) to the specified angle. In practice, though, platforms won't synthesize oblique to _arbitrary_ angles, but will synthesize to some specific angle.

If a number is _not_ provided and the font _is_ a variable font with a slnt axis, then I can understand there being uncertainty as to what angle should be requested. Potentially, a [format 3 Axis Value Table](https://docs.microsoft.com/en-us/typography/opentype/spec/stat#axis-value-table-format-3) (AVT) in the 'STAT' table could be used for this. An AVT describes a particular value on a particular axis for the family, and format 3 allows the developer to indicate a "style-linked" paired value to the "Regular" instance. The spec gives examples of format 3 being used, e.g., for wght = 400 "Regular" to indicate that the style-linked pairing is wght = 700; and it gives an example for the 'ital' axis of ital = 0 "Regular" having a style-linked pairing of ital = 1. So, potentially, for a font with a slnt axis, a format 3 AVT could be used for slnt = 0 to indicate a style-linked pairing on the slnt axis of whatever angle the font designer considers the preferred "Oblique" value. 

We didn't consider this particular situation, and so this use of a format 3 AVT hasn't been called out. But if it can solve a CSS problem, then perhaps it could get called out in some way. There'd still be a need to educate font tool vendors and font developers.

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Received on Tuesday, 3 July 2018 05:31:03 UTC

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