[Webkit-unassigned] [Bug 69282] [chromium] some Japanese punctuation displayed wrong in vertical writing in Chromium Linux

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=69282





--- Comment #8 from Koji Ishii <kojiishi at gmail.com>  2012-05-02 23:22:15 PST ---
>From the description in bug 80072, I understand this bug is a feature request to synthesize vertical alternate glyphs when the font doesn't have one. It'd be helpful if title and/or description makes the point clearer.

(In reply to comment #6)
> (In reply to comment #5)
> > If there is no vert table in the font, but there is Unicode corresponding vertical presentation form in the font, can we introduce a fallback mapping table so that those glyphs can be displayed?
> 
> There are two kinds of relevant tables/features. 
>  1.  ‘vhea’/ ‘vmtx’ to provide vertical metrics
>  2.  ‘vert’ or ‘vrt2’ GSUB features for mapping horizontal punctuations to vertical ones
> 
> It seems you are talking about 2. Yes, we can retrieve 'vert' or 'vrt2'  from a font with good font.

Unfortunately, no, it doesn't work. 'vert' is just a mapping table from a glyph ID to another glyph ID. The font must have corresponding glyphs to map to.

It is somewhat possible to synthesize vertical alternate glyphs, but it's a lot more work than you think:
1. Identify code points to rotate in vertical flow, and rotate them, or use VERTICAL PRESENTATION FORMS if available.
2. There are some code points that need shifting; e.g., U+3001 IDEOGRAPHIC COMMA. Technically speaking, you can identify such code points, get bounding box, and make shift.
3. There are some code points that uses different glyphs; e.g., U+301C WAVE DASH or U+3300 SQUARE APAATO. I don't think you can synthesize them.

You could find such a list in "Glyphs Changes for Vertial Orientation" section at http://www.unicode.org/reports/tr50 (note that the spec is still under development at this point)

So, that says, it's a good amount of work, and you can only get low-quality results for 2, and still can't get 3.

I'm not very familiar with the situation of East Asian fonts on Linux these days, but I guess it's getting better and you could find at least a few fonts that have 'vert' table. If that's the case, I would recommend not to fix this bug but wait for other fonts to support 'vert'.　If you're looking for Japanese fonts, I think IPA Mincho is a good free font.

If that's not the case -- i.e., there's really not a good fonts on Linux and there's no hope to improve in near future -- I think you should demonstrate the importance to synthesize vertical alternate glyphs even if its quality isn't good.

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