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Re: [csswg-drafts] [css-fonts] Any proposals to make CSS font-size-adjust work better for all scripts? (#4540)

From: John Hudson via GitHub <sysbot+gh@w3.org>
Date: Wed, 18 Dec 2019 16:58:56 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-567120391-1576688335-sysbot+gh@w3.org>
> So, if the measure of whatever value the user wants to adjust is available...

There's the rub. For some scripts, we have font data that, if accurately set, can be used to determine scaling adjustment values. The way CJK ideographs conventionally make use of the em square actually make these relatively easy to handle. But there's a whole raft of scripts for which we don't have specific font data, and which don't have strongly conventional relationships to existing general or Latin-centric font data. There's no data point in fonts to identify the head line height for Devanagari etc., or the base form height for Tamil etc., etc.. So for most of the world's writing systems the measure of whatever value the user wants is _not_ available except in the measuring of the topography of actual glyphs.

There's been talk in the past about extending the BASE table structures to include script and language system specific vertical metrics for linespacing purposes. Perhaps there is also some way to also include design-specific feature metrics akin to the Latin x-height metric, although I'm not sure how one makes this thorough enough or open enough to cover everything. It implies identifying the key metric(s) for each script, and I'm cautious about such an approach for some writing system: e.g. the key metrics in a naskh Arabic style might not be the same in a nastaliq style.

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Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/4540#issuecomment-567120391 using your GitHub account
Received on Wednesday, 18 December 2019 16:58:58 UTC

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