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[css3-writing-modes] The original issues of font-dependent glyph orientation

From: Koji Ishii <kojiishi@gluesoft.co.jp>
Date: Wed, 28 Sep 2011 03:48:46 -0400
To: "www-style@w3.org" <www-style@w3.org>
Message-ID: <A592E245B36A8949BDB0A302B375FB4E0CF6977301@MAILR001.mail.lan>
It took a while, but I'm going to explain the original issues fantasia and I wanted to solve by font-dependent glyph orientation. The intention is that, since several people are against using font-dependent glyph orientation, I'd like to explain why we introduced the method, and hope someone to come up with alternate ways to solve the original issues.

There are two types of issues and therefore two types of font-dependent glyph orientation were proposed. I originally thought the two issues are the same, so the current spec covers only one of them and the other is not written out yet.

1. Upright if the font is (or looks like) East Asian, otherwise sideways

This is a proposal to solve unified code points issue in Unicode, explained in another thread[1]. In short, some code points in some blocks are expected to set upright in common sense and existing text data assumes such behavior, but they're distributed across Unicode blocks due to unification process in Unicode.

It's a very long standing issue. I would very appreciate if someone can come up with how to solve this.

Here're ideas I've seen so far (I hope I didn't miss anything):
1. Make all of them upright.
2. Make all of them sideways.
3. Use font information to switch (the current spec)
4. Use lang attribute to switch.
5. Use contextual information to switch.
None of them can perfectly solve this issue. I wonder, there's no perfect solution and it's a matter of trade-offs.

2. Use vertical alternate if exists, otherwise sideways

This method is not in the current spec, but we discussed in this ML a little ago. Fantasai and I started discussing on this to make visual consistency, and I hope everyone agrees with that the visual consistency is one of important features we would like to achieve.

This issue occurs when a font designer wants the glyph to be displayed sideways, but would also like the glyph or its position optimized for vertical flow. Examples are:

U+2014 EM DASH
U+25xx Box Drawing

If they're set U, most East Asian fonts have vertical alternate glyphs for these code points, so users see them in sideways and the layout looks good for East Asians. However, users without East Asian fonts will see them in upright.

If they're set S, the glyph orientation is consistent, but vertical alternate glyphs are not used and therefore the result is not optimal for East Asian users.

As long as I tested, many software doesn't solve this issue at all; they just set U and disregard visual consistency for whom without East Asian fonts. Since "text-orientation: upright-right" is the value for East Asian documents, that's one way to solve this issue if we can agree.

Note that this may not be an issue for UTR#50 as the issue does not come up if you don't think about optimal layout and vertical alternate glyphs, both of which may not be the scope of Unicode, I'm not sure.

[1] http://lists.w3.org/Archives/Public/www-style/2011Sep/0472.html

Received on Wednesday, 28 September 2011 07:48:44 UTC

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