Re: 28th IUC paper - Tamil Unicode New

From: Adam Twardoch (
Date: Mon Aug 22 2005 - 11:54:22 CDT

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    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):

    Adam Twardoch
    Fontlab Ltd. /

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