At 08:43 AM 17-07-02, Peter_Constable@sil.org wrote:
>In Graphite, character sequences get mapped into glyph sequences one-to-one
>via the cmap, just as in OT and AAT. From that point, what happens and what
>can happen is completely at the discretion of the font developer. They can
>decide to always form certain ligatures, always form some ligatures but
>make others dependent upon ZWJ, or they may make some/all dependent upon a
>user-selected font feature (assumes the software exposes an UI for
>selecting the features that the font supports). Of course, nothing happens
>unless the font developer included rules that make it happen.
Presumably, though, making ligature lookups dependent on ZWJ in Graphite --
as in OpenType -- relies on the ZWJ character actually being painted. One
of the issues I am looking at with ZWJ is treatment of that character as an
unpainted control character in some systems and applications. If a glyph is
never painted, it doesn't matter how many font lookups include the glyph:
nothing is going to happen.
MS Office apps treat ZWJ as a control character by default and will not
paint the glyph. However, users have the option to turn on visual display
of control characters -- ZWJ, ZWNJ, LTR, RTL etc. -- in order to be able to
see them and to figure out what is affecting text in what ways. My guess is
that, at this point, all those ZWJ lookup sequences in the font would
suddenly become active, ironically achieving the opposite of what the
'display control characters' function is intended to achieve, since the ZWJ
glyphs, where processed by lookups, would disappear and be replaced by
ligatures. This is actually quite funny.
John Hudson
Tiro Typeworks www.tiro.com
Vancouver, BC tiro@tiro.com
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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