[Webkit-unassigned] [Bug 227353] Font optical sizing is broken when set to default value

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=227353

--- Comment #12 from Stephen Nixon <stephen at arrowtype.com> ---
Also, I do think the nature of this bug has changed slightly...

Previously, when a font was set to the default opsz, it would render as the max opsz. (If I am remembering correctly.)

Now (as tested in Safari Version 17.4), when a font is set to its default opsz, it instead renders with the opsz set to its current font size.

Another way to say this: `font-variation-settings` is ineffective for opsz when it is set to a font’s default axis values. It should force a particular variation setting for opsz, but instead it acts like `font-optical-sizing: auto;` for that one value.

This may not matter in many cases, but for example, it could be a problem if a website tried to set large headlines in a small opsz value, for aesthetic or high-legibility purposes. It also may disrupt "type testers" on font foundry websites. As a good example, check out Source Serif 4 Variable on Adobe Fonts:

https://fonts.adobe.com/fonts/source-serif-4-variable?vf-axes=opsz%2C20%2Cwght%2C400&vf-font-size=100&vf-font=SourceSerif4Variable-Italic

When the sample is set to its default opsz=20, it appears as opsz=60, as that is closest to its current font size (100px). If that opsz axis is moved at all, it jumps to the correct value on either size of opsz=20. This is basically just showing the same thing as the initial test case in this issue, but it may be a clearer example, and it is a live website that is representative of a place the bug is a genuine problem.

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