From: Richard Wordingham (richard.wordingham@ntlworld.com)
Date: Mon Jun 13 2005 - 21:07:20 CDT
From: "Mete Kural"
To: <unicode@unicode.org>
Sent: Tuesday, June 14, 2005 1:49 AM
Subject: Re: Arabic letters separated by markup
> >The information is there, in the data for cursor positioning data in the
>>GPOS data for ligatures in the font.
>
> Hmm.. that's an interesting point. Although I did a little experiment and
> cursor positioning data does not seem to give a reliable estimate as to
> where the component character boundaries may lie within a ligature.
> Do you know in what form this cursor positioning data is stored within the
> font file? Is it basically an x-coordinate for where the cursor should be
> positioned within the glyph?
Yes and yes. However, it's in the GDEF table, not the GPOS table (faulty
memory). For details, see
http://www.microsoft.com/typography/otspec/gdef.htm , especially Examples 4
to 6. A font does not have to contain this data - if it is absent, the
glyph will just be chopped up into portions of equal length. I think that
is what has happened in your examples. I believe a y-value would be for
vertical writing.
Richard.
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