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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: Mon, 08 Jun 2020 18:05:55 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-640785962-1591639554-sysbot+gh@w3.org>
I asked Miles specific questions about what opsz instance selection is being made in a number of different situations on the Apple platform, and in each case Miles' answer, if accurate, indicated that they were treating the opsz unit as 1/72 of a physical inch (or as near as possible given particular displays). On that platform, the way they scale CSS px relative to points means that they can use px equivalence for opsz instance selection, because they treat

1 CSS px = 1 physical pt = 3/4 CSS pt

So if text in the browser were specified at 12 CSS pt, they would be using a 16 opsz instance, because that corresponds to their scaling of the type to match what they do across their platform. Given that scaling, requesting the opsz instance in terms of px is just a convenient way of them getting the appropriate size instance for their platform, i.e. they're not actually treating the opsz unit scale as px, but passing px is the method they use internally to translate opsz units to the scaling of type on their platform.

Where things seem to have gone wrong is in other browser makers not understanding the reason Apple was passing px, and why it wouldn't make sense to do that outside of the Apple platform and its specific scaling behaviour.

GitHub Notification of comment by tiroj
Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/4430#issuecomment-640785962 using your GitHub account
Received on Monday, 8 June 2020 18:05:57 UTC

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