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

From: Eric Muller <emuller@adobe.com>
Date: Fri, 30 Sep 2011 15:08:34 -0700
Message-ID: <4E863DE2.7030809@adobe.com>
To: www-style <www-style@w3.org>
On 9/28/2011 11:22 AM, Koji Ishii wrote:
> If you look at font tables[1], they match to their input systems; MS Gothic, Meiryo, and Kozuka Gothic on Windows has vert feature for U+2015 but not for U+2014, while Hiragino on Mac has vert feature for U+2014 but not for U+2015.

My take is that the 'vert' feature is ill-defined, but that we need to 
implement a decent layout on top of it, the way it is today. (there are 
other similar cases, e.g. U+00B0 ° DEGREE SIGN, which do not have the 
added complication of the confusion between U+2014 and U+2015).

My proposal is essentially to restrict the application of 'vert' to 
those cases where it is absolutely necessary (e.g. square katakana, 
ideographic stop, etc), and in particular not use it for the dashes 
where it's not that useful. Hopefully, all the common fonts have done 
(in the same way) the cases where it's absolutely necessary to go 
through a feature, and differ only on those cases where we don't really 
need to apply 'vert'.

In more concrete terms, the UTR 50 draft now has three orientations: U, 
S, and T (for Transformed). T is for square katakana symbols, the weavy 
dash and a handful of others. The T are defined purely in terms of 
Unicode. Think in terms of Unicode code charts: What the charts show 
today is a representative glyph for horizontal lines.  Let's say we want 
to produce the code charts for vertical lines: most cases will the same 
glyph either Upright (=as is) or Sideways (= rotate 90 degree 
clockwise), but a few are Transformed.

Not surprisingly, the 'vert' feature does the same thing on Ts in all 
fonts (well, all those that support vertical Japanese text). So 
restricting 'vert' to the Ts gives a reliable system.

This will also give us decent layout. We can get great layout by adding 
a new feature, which will be restricted to change the shape of glyphs 
but not incorporate a rotation aspect. Because of that restriction, this 
new feature can be applied liberally and give a lot of freedom to the 
font designer, without putting the layout engine in a loose-loose situation.

Note that 'vert' does not have this restriction of "free to change the 
shape, but do not rotate". This is precisely what makes it so hard to 
use when it's not done the same across fonts. Since we cannot come back 
on that, we have to either use 'vert' only in the most restricted 
circumstances, or to react to whether it actually changed the glyph 
(which I find way too problematic).

Eric.
Received on Friday, 30 September 2011 22:09:13 GMT

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