Re: [csswg-drafts] [css-inline] Define how to synthesize `ideographic-over` and `ideographic-under` (#10850)

> This is currently defined in https://www.w3.org/TR/css-inline-3/#baseline-synthesis ; though if it needs some improvement, we can improve it.

Thank you for the pointer, I didn't know the section. I read it, but I'm not sure if I understand the algorithm in this section. Can you help?
> 1. The [central baseline](https://www.w3.org/TR/css-inline-3/#central-baseline) is defined to be halfway between the [ideographic-over](https://www.w3.org/TR/css-inline-3/#ideographic-over-baseline) and [ideographic-under](https://www.w3.org/TR/css-inline-3/#ideographic-under-baseline) baselines, so any two of these determines the third.

and the [central baseline](https://www.w3.org/TR/css-inline-3/#central-baseline):
> Corresponds to the ideographic central baseline, halfway between the [ideographic-under](https://www.w3.org/TR/css-inline-3/#ideographic-under-baseline) and [ideographic-over](https://www.w3.org/TR/css-inline-3/#ideographic-over-baseline) baselines. Assigned to bsln value 1 in TrueType AAT.

Am I reading this correctly that this is defined from each other? I'm having difficulty to understand what it suggests when all of them are missing. If it means to fallback to the item 3:
> 3. In CJK fonts the [ascent](https://www.w3.org/TR/css-inline-3/#ascent-metric) and [descent](https://www.w3.org/TR/css-inline-3/#descent-metric) typically match the [ideographic-over](https://www.w3.org/TR/css-inline-3/#ideographic-over-baseline) and [ideographic-under](https://www.w3.org/TR/css-inline-3/#ideographic-under-baseline) baselines, so can be used as a fallback when both are missing.

Is this suggesting to use ascent/descent as the synthesized ideographic-over and ideographic-under? For `text-box-trim`, using ascent/descent means that it's the same as `text`. [This Japanese article](https://qiita.com/rhrh__8/items/b1fbfaf6b604a3ffb8b0) and [another Japanese article](https://goodpatch-tech.hatenablog.com/entry/figma-web-zure-shitteokou) indicates that using ascent/descent doesn't help for the vertical centering and alignment purposes for CJK fonts. For Meiryo, Hiragino, and Noto (Chrome/Firefox/Safari default Japanese fonts), ascent/descent don't match the desired position of ideographic-over and ideographic-under.



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Received on Friday, 13 September 2024 09:19:44 UTC