Re: The Yoruba under-diacritic

From: Adam Twardoch (list.adam@twardoch.com)
Date: Thu Jan 27 2005 - 13:53:10 CST

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    > Are there ways that software can handle different characters and
    > combinations of
    > characters as equivalents in certain language settings?

    To ensure portability of texts, it would be advisable to agree upon just one
    certain combining character to be used for Yoruba, preferrably U+0323 (dot
    below). With OpenType Layout, the font developer can provide mappings from
    the default glyph for the U+0323 character to stylistic alternate glyphs for
    that character. It is possible to set up the alternates only to work for the
    Yoruba language context.

    An OpenType font could contain the glyph "dotbelowcomb" which would be the
    default form for the character (an actual dot below). The glyph would be
    encoded as U+0323 in the "cmap" table of the font. In addition the font
    could, for example, contain 4 different Yoruba stylistic alternates for the
    character: "dotbelowcomb.ss01_YBA", "dotbelowcomb.ss02_YBA",
    "dotbelowcomb.ss03_YBA", "dotbelowcomb.ss04_YBA".

    The font would then include a "GSUB" table several OpenType Layout features
    that allow the user to select a different set of accents upon his
    discretion. In AFDKO source code notation, the features could read like:

    feature ss01 {
      language YBA;
      sub dotbelowcomb by dotbelowcomb.ss01_YBA;
    } ss01;
    feature ss02 {
      language YBA;
      sub dotbelowcomb by dotbelowcomb.ss02_YBA;
    } ss02;
    feature ss03 {
      language YBA;
      sub dotbelowcomb by dotbelowcomb.ss03_YBA;
    } ss03;
    feature ss04 {
      language YBA;
      sub dotbelowcomb by dotbelowcomb.ss04_YBA;
    } ss04;

    In an application that supports language-sensitive OpenType Layout features,
    the user could then select the appropriate stylistic variant of the
    dot-below accent when the text is marked as set in Yoruba. There are
    currently no such shipping applications, unfortunately, but support for
    language-sensitive OpenType Layout features will be included in the the new
    "WinFX" graphic subsystem of Windows Longhorn.

    Regards,
    Adam Twardoch



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