[CSS-Font] Fixing font-variation-settings: "ital" 1 with font style of italic and oblique

[wjhe1016]

Currently chromium is having issue with when font-variation-settings: "ital" 1 and font-style: italic, font-style: oblique, <i>HTML element.
See bug

According to CSS spec If a variable font has an Italic (ital) axis, ital axis should be activated (turned to value "1") by the CSS font-style:italic or font-style:oblique and the html <i>. but currently in chromium is having issues with that.

I uploaded a CL in chromium in here (passed the CQ dry run).

This image below is before the fix in this test:

After (in progress)

Since CSS spec is unclear on what should happen when font-variation-settings: "ital" 1 and font-style: oblique ±XXdeg, I had made a proposal including in this doc.

[jfkthame]

I think it's wrong for font-style: oblique to activate the ital axis in the font, which is what the "after fix" image seems to show for the combination of font-style: oblique and "Font with ital, 0 to 1".

If oblique is requested, and no actual oblique face nor slnt axis is available, the browser should not fall back to an italic face; instead, it should apply a synthetic oblique effect. Just as it should not use a distinct italic face as fallback for oblique, I think it should also not apply the ital axis.

[wjhe1016]

@jfkthame That makes sense. 🤔 I will change my code.
Currently I have seen in Gecko 143.0 is doing the perfect setting. I will try to make the font setting the same as Gecko 143.0.

[svgeesus]

The spec currently says (my emphasis)

oblique <angle [-90deg,90deg]>
Controls matching against an oblique face. Positive angles represent a clockwise slant; negative angles represent a counter-clockwise slant. The lack of an <angle> represents 14deg. (Note that a font might internally provide its own mapping for "oblique", but the mapping within the font is disregarded.) Fractional and negative values are accepted; however, values less than -90deg or values greater than 90deg are invalid. If no oblique faces exist, and font-synthesis-style has the value auto, a synthetic oblique face will be generated.

[svgeesus]

@jfkthame @wjhe1016 is the spec clear as-is or is clarifying wording needed?

[drott]

I think it's wrong for font-style: oblique to activate the ital axis in the font, which is what the "after fix" image seems to show for the combination of font-style: oblique and "Font with ital, 0 to 1".

I support that statement.

[wjhe1016]

@svgeesus I think more clarification is better for ital axis. I will adjust my CL and try to fix this issue and make it the same as Gecko 143.0.