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[csswg-drafts] [css-inline] baseline synthesis: add ideographic embox and baseline offset

From: Nat McCully via GitHub <sysbot+gh@w3.org>
Date: Wed, 08 Nov 2017 21:38:01 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-272358571-1510177080-sysbot+gh@w3.org>
macnmm has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-inline] baseline synthesis: add ideographic embox and baseline offset ==
https://drafts.csswg.org/css-inline/#baseline-synthesis

The most important metrics for CJK layout are the ideographic embox top and bottom, and the roman baseline offset (the distance from the embox bottom to the roman baseline). Ideographic character face, as described, is not that useful as a baseline for text, and I would recommend it be eliminated from the baseline selectors.

The distance from embox top to embox bottom in a square font is equal to the point size of that font. The offset of the embox to the Roman baseline is set so that the capital Roman letters are centered within that embox. Normally that also results in the CJK glyphs also to be centered in the embox.

The Text Top and Text Bottom baselines are overloaded to be "embox top and bottom", but it is unclear whether this is true for CJK fonts and non-CJK fonts in the same way, or that the ideographic embox can be obtained or calculated consistently for all fonts so they can be aligned correctly in a line together. I recommend disambiguating the text top and bottom from the CJK ideographic embox top and bottom.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/1961 using your GitHub account
Received on Wednesday, 8 November 2017 21:38:06 UTC

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