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Re: [csswg-drafts] [css-text][css-fonts] Optical bounds of a line (#5466)

From: Laurence Penney via GitHub <sysbot+gh@w3.org>
Date: Sun, 27 Sep 2020 20:47:47 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-699686373-1601239666-sysbot+gh@w3.org>
Here’s a demo I made on the issue a few years ago, and [referred to the MPEG-OTSPEC list](https://lists.aau.at/pipermail/mpeg-otspec/2020-September/002355.html) earlier this month.


Look at the third example, set in Source Sans with optically zeroed sidebearings and spaced with CSS `letter-spacing`.

My proposal was that fonts can be made with glyph sidebearings aligned to optical left and optical right bounds (just as glyphs are aligned to the font’s baseline and cap-height). In CSS terms it’s like removing horizontal padding. Then, spacing can be applied via one of:
* CSS `letter-spacing`
* the tracking feature in an app
* a variable spacing axis in the font

Back in 2013, Cameron Booth on his Transit Maps blog published a good tutorial on dealing with the issue in Illustrator:
* [Tutorial: Working with Point Type Labels in Adobe Illustrator](https://www.transitmap.net/point-type/)

> you need to be aware that the text you type almost never aligns with the point that you’ve created. Because of the letter spacing that’s baked into each character, there’s a small – but noticeable – gap between the point and the adjacent character 

BTW, making the above tests alerted me to be a bug or an underspecification, such that CSS `letter-spacing` is applied after every glyph _including glyphs at the end of a line of justified text_.

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