Re: 28th IUC paper - Tamil Unicode New

From: Richard Wordingham (
Date: Mon Aug 22 2005 - 15:02:54 CDT

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    Adam Twardoch wrote:

    > 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.

    So how do I get it to live up to its 'responsibility' to support an Indic
    conlang living in the PUA? I'm not even sure that Burmese is supported yet.

    I deliberately framed the question in terms of an encoding that Uniscribe
    would not recognise as a complex script. It's not even clear to me whether
    the feature 'ccmp' would be available, nor whether it can really be used to
    effectively swap two glyphs. My doubts on the latter point arise because
    Uniscribe has to maintain some sort of mapping between position and
    characters to support selection, insertion and deletion. Using GSUB to do
    the re-ordering in Devanagari might put quite a strain on the maintenance of
    this mapping - Tamil would be simpler.

    While it clearly looks like good practice to have a single per-script
    definition of necessary re-orderings, in practice it is very inconvenient if
    the user (or system administrator) cannot update the definitions. For
    example, Microsoft has little incentive to modify Uniscribe to treat
    independent Devanagari vowels as consonants (or, to be pedantic,
    consonant-vowel ligatures).


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