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[css3-fonts] Language-specific display and 'locl' feature (was RE: [css3-writing-modes] The original issues of font-dependent glyph orientation

From: Koji Ishii <kojiishi@gluesoft.co.jp>
Date: Fri, 30 Sep 2011 18:10:29 -0400
To: Taro Yamamoto <tyamamot@adobe.com>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <A592E245B36A8949BDB0A302B375FB4E0CF6977584@MAILR001.mail.lan>
This is a separate issue from glyph orientation so I'm changing subject. I'm not sure if this should belong to fonts or linebox though.

Taro is talking about yet another issue in EM DASH for East Asians. EM DASH in Latin scripts are designed to match to the center of x-height, while East Asians need it match to the center of em box. It's been a long standing issue for East Asian font designers. Some font designers chose to use Latin-positioned EM DASH for U+2014 even in East Asian fonts, which might be one of the reasons East Asian EM DASH was mapped to U+2015 in some platforms.

His idea is to use 'locl' GSUB/GPOS feature[1] to adjust glyphs and positions. Is this supported in CSS3 Fonts?

The current spec has "Language-specific display"[2], but I can't understand which part of OpenType the 'lang' attribute should be used. Is this only applied to select lookups from features, or does it include 'locl' feature?

By "select lookup" I mean picking up appropriate lookup table from TrueType/OpenType format as in page 11 of [3]. I guess it's talking about this, am I correct?

[1] http://www.microsoft.com/typography/otspec/features_ko.htm#locl
[2] http://dev.w3.org/csswg/css3-fonts/#language-specific-support
[3] http://hackipedia.org/File%20formats/TrueType/v2.00%20OpenType/ttoch02.doc.pdf

Regards,
Koji

-----Original Message-----
From: Taro Yamamoto [mailto:tyamamot@adobe.com] 
Sent: Thursday, September 29, 2011 5:00 PM
To: Koji Ishii; www-style@w3.org
Subject: RE: [css3-writing-modes] The original issues of font-dependent glyph orientation

Ishii-san,

> I talked with Taro Yamamoto today and we found an interesting case for 
> 2nd issue.

After the conversation with you yesterday, I considered this issue some more. My current idea is that the issue, viz. of a group of dash and ellipsis characters that need to show different glyph shapes (the Japanese EM-box centered and the roman adjusted for lowercase), depending on the language context, can be solved by applying the 'locl' or some appropriate GSUB feature to the glyphs mapped from the U+2014 (and other similar related glyphs, such as 2-EM dashes and ellipses, etc). Eric might have his own comments, though.

Regards,

--Taro
Received on Friday, 30 September 2011 22:10:08 GMT

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