[XeTeX] On combining diacritics again
jonathan_kew at sil.org
Mon Jan 23 17:14:22 CET 2006
On 23 Jan 2006, at 12:23 am, Will Robertson wrote:
> On 23/01/2006, at 9:04 , Adam Twardoch wrote:
>> I'll just add that in Mac OS 10.4.0-10.4.2, if a font included
>> both AAT and OpenType Layout features, the OpenType Layout
>> features were used. As of 10.4.3, the behavior was changed (and
>> rightly so) and AAT features are given preference.
> Just getting a bit off-topic here -- I can understand that for
> backwards compatibility this is totally the way to go here, but are
> new fonts being implemented with AAT tables at all now?
Yes, at least in a few cases.
> And if so, is it just because Mac OS X doesn't support OpenType
> well enough?
> Or are there still relevant areas of AAT that are superior to
Each technology has some particular strengths and weaknesses; neither
is superior in every respect.
Personally, I think AAT's greatest weakness in comparison to OT is
the lack of a dynamic mark attachment mechanism; this makes it
virtually impossible to support arbitrary sequences of diacritics on
a base character (as opposed to supporting a predetermined, limited
set of combinations).
On the other hand, AAT allows the font designer to create new layout
features, provide them with human-readable (even localized) names,
and expose them through the app's user interface (e.g., the
Typography panel), with no code changes in any layout engine or app.
In the OT model, this would require updates to the code of all client
applications (or a shared library they use). So AAT gives the font
designer much greater freedom--and control--in this area, which is a
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