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

From: Myles C. Maxfield via GitHub <sysbot+gh@w3.org>
Date: Thu, 17 Oct 2019 18:59:21 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-543315394-1571338760-sysbot+gh@w3.org>
The observation that we made when we implemented optical sizing is that 1 typographic point = 1 CSS pixel.

This is clearly true: Safari, Firefox, Chrome, Pages, Microsoft Word, raw Core Text, and TextEdit all agree. Here is an image of Ahem rendered in all of those using a size of 48 typographic points:

![Screen Shot 2019-10-17 at 11 51 35 AM](https://user-images.githubusercontent.com/918903/67038739-d6dc3700-f0d4-11e9-84ac-b83c3aae5098.png)

You can see that it's the same size in all of these different apps. In addition, Pages even puts units on the font size: "pt" and the documentation for raw Core Text (the second to rightmost app in the above image) also [indicates](https://developer.apple.com/documentation/coretext/1509153-ctfontcreatewithname?language=objc) that its size is in points:

> The point size for the font

So, when we apply an optical-sizing value of X typographic [points](https://docs.microsoft.com/en-us/typography/opentype/spec/dvaraxistag_opsz), that is equal to CSS pixels, and we apply this correctly.

I'm not making a point about what the designers of desktop typographic systems intended to be true. Instead, I'm making a point about what is, de facto, true in reality.

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Received on Thursday, 17 October 2019 18:59:23 UTC

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