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

We're talking about _optical_ design variation, i.e. tuning design to specific optical size. I could easily make the case for defining degrees of visual angle as being the most appropriate unit for opsz, but the point is that in order to be something targetable _in design_ the unit needs to be an absolute physical measurement because we have — better or worse — absolute physical eyes.

So type designers and, I believe, the authors of the opsz axis specification, understood ‘typographic point’ to be 1/72 of a physical inch. So Miles' observation that

> it appears that the size of a typographical point is different between Windows and macOS / iOS

suggests to me that a) the spec fails to explicitly state what is meant by ‘typographic point’, and b) different people are using the term in different ways.

I think I understand Miles’ explanation of why there are CSS points, and Cocoa points, and probably other points, but there needs to be one term that refers explicitly to 1/72 of a physical inch, because that's the unit that type designers are targeting.

I'm not enthused about redefining opsz as having a px unit scale, because I suspect from what I have read here that everything that has been said about pt is also true for px: it isn't an absolute measurement, there are different kinds of px, there are different sizes of px, there are different numbers of px in different kinds of points, inches, etc..

The issue here isn't just of consistency in implementation — of getting the same opsz instance for the same _nominal_ type size in different platforms —, but getting the opsz instance that the type designer has created for an _actual_ size. Otherwise there's no point in calling this optical.


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Received on Thursday, 21 May 2020 22:43:08 UTC