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[ft] What do kerning values mean in RTL text?

From: Paul Pedriana
Subject: [ft] What do kerning values mean in RTL text?
Date: Fri, 09 Jun 2006 12:14:43 -0700
User-agent: Mozilla Thunderbird 1.0.7 (Windows/20050923)

I'm trying to understand how kerning is done in RTL text and can't find any documentation (on the Internet nor in Freetype) that addresses this.

- Do kerning pairs in RTL refer to two sequential glyphs in logical order or visual order?

- If there is a string with the logical order is CAT and a visual order of TAC, do kerning adjustment pairings apply for CA (logical order) or for AC (visual order)?

- Given that the RTL layout alrogithm ( specifies that advance width of C (from our CAT above) is applied before the positioning and drawing of C, how and when and in what way is a kerning adjustment applied?

If I can get this answered, I would like to document this and contribute the documentation to the Freetype project, as this is something that appears to have flummoxed a lot of people. Every description of kerning I can find discusses LTR kerning and unfortunately seems to leave RTL kerning as an "exercise for the reader".


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