Re: DIY OpenType Re-ordering

From: Richard Wordingham (
Date: Thu Mar 23 2006 - 14:41:11 CST

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    Philippe Verdy wrote:

    >From: "Richard Wordingham" <>

    > I don't know what you designate by the "base character", because in Indic
    > scripts it happens quite often that this base character (around which
    > diacritics and other letters are visually composed) is encoded in the
    > middle of the cluster, or that the first encoded character will appear in
    > the middle of the string of glyphs that compose a cluster.

    By 'base character' I meant the first consonant of the cluster in the
    encoding sequence.

    > For Unicode, the base character is not that one, it's only the start of a
    > combining sequence, and we all know that a combining sequence is less than
    > an Indic cluster (notably when there are multiple consonnants separated by
    > halant so that some of them are dead consonants, or when there are ZWNJ
    > and ZWJ at end of a consonnant cluster).

    Is it appropriate to call a Unicode virama acting as a control character a
    halant? I thought a halant was a visible mark.

    > But I still don't know any locale-sensitive conjunct that has special
    > reordering or composition rules (The encoded Marathi letters in the
    > Devanagari block for example don't have final dandas, so the half-form and
    > repha problem does not apply to them and they apparently don't need
    > complex reordering rules, but there may be cases where subjoined forms may
    > occur and should be controled, complexifying the regexps that the font
    > reordering algorithm uses to match the cluster patterns and then select
    > their corresponding string of glyph ids.)

    Hindi and Sanskrit apparently have different rules for when a conjunct is
    preferred to the use of a half-form. Reportedly almost every consonant or
    conjunct in Marathi has a half-form, even though the half-form may look like
    the full form plus halant. (It can't be a halant, because the short i-matra
    precedes the half-form. :-)

    > My opinion is that a font has to match a style that first works according
    > to a single locale, and that locale variations are defining a new,
    > separate style, which should be supported in another font, or in a
    > composite OTC font with alternate names to match those styles. In that
    > case, no specific "feature" must be selectedor enabled by the application,
    > it just selects the font by name according to the expected style.

    Isn't this 'locale' feature what the OpenType 'language system' is for?


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