RE: ZWJ and Latin Ligatures

From: John Hudson (
Date: Thu Jul 04 2002 - 13:33:02 EDT

At 19:55 7/2/2002, Marco Cimarosti wrote:

>The OpenType specs published on the Adobe site states that table GSUB has a
>subtable to handle ligatures ("LookupType 4: Ligature Substitution
>It says that "A Ligature Substitution (LigatureSubst) subtable identifies
>ligature substitutions where a single glyph replaces multiple glyphs"
>(multiple *glyphs*, not multiple characters).
>OK: literally speaking, it is true that OT maps single characters to single
>glyphs, but then it maps multiple glyphs to ligature glyphs, so what's the
>I mean: isn't this two-step mapping:
> code point -> glyph ID
> component glyph ID's -> ligature glyph ID
>functionally equivalent to an hypothetical one-step mapping?
> component code points -> ligature glyph ID
>Am I missing something?

Well, what you might be missing is layout feature support, in which case
the sequences described might be 'dysfunctionally equivalent'. It is useful
to maintain a distinction between direct (cmap) and indirect (GSUB lookup)
glyph-to-character mapping, because of the system and application support
issues involved in getting the latter to work.

John Hudson

Tiro Typeworks
Vancouver, BC

Language must belong to the Other -- to my linguistic community
as a whole -- before it can belong to me, so that the self comes to its
unique articulation in a medium which is always at some level
indifferent to it. - Terry Eagleton

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