From: Adam Twardoch (list.adam@twardoch.com)
Date: Mon Aug 22 2005 - 11:54:22 CDT
Richard Wordingham wrote:
> By the way, why can't font-encoded Tamil (e.g. using ASCII codes as a
> hack) display be handled on Windows by a GSUB table that handles the
> re-ordering? Or would that make it Level-2 anyway? Where can I find a
> definition of 'Level-2'?
GSUB tables don't handle the reordering in Indic languages. It's the
responsibility of the OpenType Layout processor, e.g. Uniscribe.
OpenType rendering, unlike AAT, relies on a two-tier model where some
generic writing-system-related behaviors are always handles in the same
way by the OpenType Layout processor and are not explicitly stored in
the fonts. Only typeface-specific behaviors are stored in the GSUB and
GPOS tables in the font. This means that the OpenType Layout processor
must make assumptions about certain Unicode codepoints and certain
features being present in the font. It reads in the Unicode string,
applies the hardcoded writing-system-specific behaviors that are not
stored in the font (e.g. the reordering) and then the typeface-specific
behaviors that are stored in the font (e.g. vowel positioning).
For more information, you can read (in the recommended order of reading):
http://www.microsoft.com/typography/OpenTypeDevIntro.mspx
http://www.microsoft.com/typography/Glyph%20Processing/intro.mspx
http://www.microsoft.com/typography/OpenType%20Dev/indic/intro.mspx
http://www.microsoft.com/typography/otfntdev/tamilot/default.htm
Regards,
Adam Twardoch
Fontlab Ltd. / MyFonts.com
This archive was generated by hypermail 2.1.5 : Mon Aug 22 2005 - 11:55:43 CDT