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Re: [csswg-drafts] [css-inline-3] About the central baseline (#5177)

From: CSS Meeting Bot via GitHub <sysbot+gh@w3.org>
Date: Wed, 17 Jun 2020 17:25:36 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-645512771-1592414735-sysbot+gh@w3.org>
The CSS Working Group just discussed `About the central baseline`, and agreed to the following:

* `RESOLVED: Define the central baseline so if the font has an explicit ideographic central baseline, use that. If not, use halfway between ideographic top and bottom. If that's missing, halfway between ascent and descent`

<details><summary>The full IRC log of that discussion</summary>
&lt;Rossen_> Topic: About the central baseline<br>
&lt;Rossen_> github: https://github.com/w3c/csswg-drafts/issues/5177<br>
&lt;dauwhe> fantasai: i raised an issue about central baseline definition<br>
&lt;dauwhe> ... halfway between text top and text bottom, which are not defined<br>
&lt;dauwhe> ... and it's the default baseline in vertical writing mode<br>
&lt;dauwhe> ... which isn't interoperable, which is bad<br>
&lt;dauwhe> ... we need a good metric for Vertical writing and CJK<br>
&lt;dauwhe> ... which is halfway between ideographic top and ideographic bottom<br>
&lt;dauwhe> ... we could just define to be exactly that<br>
&lt;dauwhe> ... or create a new keyword for ideographic central<br>
&lt;dauwhe> ... but I think we should make central the ideographic baseline<br>
&lt;dauwhe> ... comments or questions?<br>
&lt;dauwhe> florian: don't have a great sense of the fallback when ideographic baselines aren't there<br>
&lt;dauwhe> AmeliaBR: use ascender and descender heights to define edge of em-box, and halfway between?<br>
&lt;dauwhe> ... that gets messy because of different values of asc and desc<br>
&lt;dauwhe> ... and there are different names for metrics<br>
&lt;dauwhe> ... if we're using central alignment on a font not designed for it, and the font is badly broken, then you get bad results<br>
&lt;dauwhe> florian: are there vertical languages that are set upright?<br>
&lt;dauwhe> ... does ??? use it?<br>
&lt;dauwhe> fantasai: ??? uses same as chinese<br>
&lt;fantasai> s/???/Yi/<br>
&lt;dauwhe> AmeliaBR: the OT fallback fallback for center on vertical axis is to assume glyphs use full em-height<br>
&lt;dauwhe> ... you'll get weird results if glyphs are narrower<br>
&lt;florian> s/are there vertical languages that are set upright/are there vertical languages that are set upright and whose fonts don't have ideographic top/bottom metric/<br>
&lt;Rossen_> s/Resolved:/RESOLVED:/<br>
&lt;dauwhe> fantasai: the proposal is to define central baseline to be the ideographic baseline<br>
&lt;dauwhe> ... and if that's missing fall back to half between ascent and descent<br>
&lt;dauwhe> AmeliaBR: the CSS definition continue to use the concept of em-box<br>
&lt;dauwhe> ... if not explicitly defined<br>
&lt;florian> wfm<br>
&lt;dauwhe> fantasai: if the font has an explicit ideographic, use that. If not, use halfway between ideographic top and bottom. If that's missing, halfway between ascent and descent<br>
&lt;dauwhe> Rossen_: any objections?<br>
&lt;dauwhe> RESOLVED: Define the central baseline so if the font has an explicit ideographic central baseline, use that. If not, use halfway between ideographic top and bottom. If that's missing, halfway between ascent and descent<br>
</details>


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Received on Wednesday, 17 June 2020 17:25:39 UTC

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