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

From: John Hudson via GitHub <sysbot+gh@w3.org>
Date: Thu, 17 Sep 2020 22:52:34 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-694542017-1600383152-sysbot+gh@w3.org>
What would be the collective use of such published scale factors, Laurence?

Collectively, I'm not sure that we do need a lot of data about different OS and device vendor scale factors. Obviously the individual OS and device vendors need to know and understand those scale factors, but for opsz to work we really do only need a couple of data, _but we need those to be reliable_. We need to reliably know that e.g. a value of 6 on the opsz axis scale corresponds to an optical size design for type at a size of 6/72 of a physical inch at a typical reading distance of 14–16 physical inches.

If that can be relied upon, then how individual OS and device vendors make opsz selection that takes into account their various scale factors is their responsibility. And if some do it better than others, and some don't get it right at all, and some offer clever ways to adjust for accessibility preferences, or for dynamic real distance, or for virtual distance in 3D environments, while others do it fairly crudely on a 'near enough' basis, that's all still their responsibility, and the font maker can and should only being doing one thing, and that's making sure the optical size design is appropriate for the nominal text size in physical points at a typical reading distance.

My big worry is that font makers start trying to target specific scale factors in particular OS or device platforms, in which case opsz is doomed.

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