Re: Windows Glyph Handling

From: Richard Wordingham (
Date: Tue Aug 23 2005 - 18:40:54 CDT

  • Next message: John Hudson: "Re: Windows Glyph Handling"

    John Hudson wrote:

    > Richard Wordingham wrote:

    >>> In the OpenType model re-ordering is specifically NOT handled at the
    >>> glyph level, but at the character level.

    >> Do you mean 'OpenType' or something like 'Uniscribe/OpenType' or
    >> 'Microsoft'?
    > I mean OpenType. The OpenType GSUB and GPOS lookup types are not designed
    > for glyph *re-ordering*. There is no mechanism within OpenType to say
    > 'take this sequence ABC and rearrange it to ACB'.

    I quote from the Context Substitution Format 1 subsection of

    'For example, if a client is to replace the glyph string <abc> with its
    reverse glyph string <cba>, the input context is defined as the glyph
    sequence, <abc>, and the lookups defined for the context are (1) "a" to "c"
    and (2) "c" to "a". When a client encounters the context <abc>, the lookups
    are performed in the order stored. First, "c" is substituted for "a"
    resulting in <cbc>. Second, "a" is substituted for the "c" that has not yet
    been touched, resulting in <cba>. '

    More generally, I would be thinking in terms of a 'ligature substitution'
    replacing BC by D (in the context of A, if you wish) followed by a 'multiple
    substitution' D to CB. The mechanism is clunky, but it exists. What could
    get very confused is cursor motion over the displayed string.


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