Re: [csswg-drafts] [css-fonts] Proposal to extend CSS font-optical-sizing (#4430)

The variable opsz axis provides a means for the font maker to tune the design of glyphs for specific sizes and size ranges (with a lot of flexibility in terms of how much or how little interpolation to rely on between size instance delta sets) and to deliver that size-specific design variation to users. How downstream clients interpret the opsz axis is in some respects up to them, but in order for everyone involved to be able to predict what the others are doing and provide the most useful and highest quality typographic tools to users, there needs to be some respect for an agreed and standardised scale. The scale unit defined in the OpenType Font Format specification is the typographic point, i.e. 1/72 physical inch. How that gets interpreted in e.g. applications that deal with visual angle and distance in VR/AR, is going to be different from how it gets interpreted in physical page layout software, but the point is that the standard scale needs to be interpreted, and pretending that the scale is px instead of typographic points isn't interpreting the scale: it's throwing it out and doing something unpredictable.

@davelab6 :
> How about a new opsx axis that is specified to pixels not points?

That's relatively easy to add to the OT axis registry, and reasonably easy to add to existing fonts with optical sizes axes — much of it could be done using the same source masters and different mapping of design space units to axis units —, but re-reading everything above I'm not sure whether it would solve the problem or not. I mean, when someone makes a reasonable case that 1/72 inch and 1/96 inch are the same thing and anyway an inch isn't an inch, I lose all certainty about anything. 😬

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Received on Thursday, 21 May 2020 04:59:20 UTC