From: Adam Twardoch (list.adam@twardoch.com)
Date: Mon Aug 22 2005 - 16:48:56 CDT
Richard Wordingham wrote:
> So how do I get it to live up to its 'responsibility' to support an
> Indic conlang living in the PUA?
As the name says, PUA is intended for "private use". Neither the Unicode
Standard nor the applications have any knowledge about the writing
system, the directionality or other properties of characters that use
PUA codepoints. To avoid redundancy of mapping information in the fonts
and reduce their complexity, the OpenType architecture uses the two-tier
model. An application needs to have knowledge about which writing system
a character belongs to, what is its directionality etc. -- and this
information is by definition not available for PUA. Other technologies
such as AAT (Apple Advanced Typography) have such information contained
in the "prop" and "Zapf" tables that are included in the font so you can
define arbitrary reorderings even for PUA characters using AAT. This
will work on Mac OS X in Cocoa applications. However, experience has
shown that the effort to develop an AAT state machine that would
reliably perform all the complex script processing within a font was
quite substantial -- this is why the OpenType technology turned out to
be far more successful than AAT. The limited flexibility of OpenType
also means limited complexity.
There are open source OpenType Layout processors available: IndiX and
ICU Layout.
http://rohini.ncst.ernet.in/indix/
http://icu.sourceforge.net/userguide/layoutEngine.html
Since they're open source, you can extend them to cover your own PUA
usage schemes.
A.
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