McEs, A Hacker Life: Advanced OpenType Features in Pango

Monday, May 14, 2007

Advanced OpenType Features in Pango

Last week I worked on bringing Pango's OpenType engine into shape. Something that has been long overdue. Not anymore.

Pango can now select arbitrary OpenType script and language systems, and in near future arbitrary OpenType features too. The basic, arabic, and syriac modules are ported to use these features. More modules to follow.

Finishing off that feature is addition of another one, that pango will read env vars PANGO_LANGUAGE or LANGUAGE and use that for making better guesses to tag runs of text with languages.

First window is rendering of Pango's test-mixed.txt using the command line pango-view tool.

Second window is the same, but with env var PANGO_LANGUAGE="en:ur". As you can notice, an Arabic font more suitable in style for Urdu is selected instead of my default Persian fonts.

Third window is vertical rendering of the same text. If you look at the last, Japanese, line, in the vertical window, the brackets around the text are correctly rotated, unlike previous versions of Pango.

This and previous works are all in Pango 1.17.0.

Labels: opentype, pango

¶ 8:48 PM

Comments:

Nice work.

But why is the one kanji character in the last sentence rendered with a different font?

# posted by

Anonymous : May 14, 2007 9:42 PM

Behdad, it's nice to see some results with Pango. Could you please demonstrate the new functionalities with different Chinese fonts?

# posted by

lacampane11a : May 14, 2007 11:49 PM

Looks like it's getting that character from the Chinese font.

# posted by

Anonymous : May 15, 2007 12:12 AM

Clare, I really like to, but I need some help as I can't really tell much difference.

As for that character in the Japanese text, yes, it's taking it from the Chinese font. If I set PANGO_LANGUAGE=ja, that will be fixed, but the Chinese text takes half of its glyphs from the Japanese font. This is a known problem with Unicode's encoding of East Asian character sets: you can't have both rendered correctly using a single font unless you assign language tags to them. In Pango speak, it's possible to set their language (using Pango markup or attributes) to get both runs correct. I will go on and do that in my test file for the future.

# posted by

behdad : May 15, 2007 1:04 AM

Oh man, you are clearly on a roll :), keep it rolling. Many thanks.

# posted by

Anonymous : May 15, 2007 3:42 AM

Hi Behdad,

I noticed a couple of issues with the Japanese sentence. Besides the font issue with the kanji character mentioned already, the period should be '。', not the English '.'. The っ (tsu) should be the smaller one; the one you have looks like the larger one.

Anyway, nice work on the feature! :)

Ben

# posted by

Anonymous : May 15, 2007 12:38 PM

Thanks Ben, committed the fix.

# posted by

behdad : May 28, 2007 4:21 PM

The punctuation looks misaligned to me. I don't know about Chinese, but in Japanese the "end of sentence marker" (small circle) and "comma" (chinese character comma, not western one) should be placed just below the preceding glyph, and should be on the right of the column of text, not centred.

# posted by

James : August 18, 2007 6:57 PM

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