From: Peter Constable (petercon@microsoft.com)
Date: Mon Feb 28 2005 - 19:12:44 CST
> From: unicode-bounce@unicode.org [mailto:unicode-bounce@unicode.org]
On Behalf
> Of UList@dfa-mail.com
> But I want to go even a little further, in order to implement *all*
the
> possible variations of archaic Greek scripts in one smart font. I want
to define
>
> OLD_CRETAN_DORIC_LTR (left to right)
> OLD_CRETAN_DORIC_RTL (right to left)
> OLD_CRETAN_DORIC_ALT_LTR (alternate, left to right)
> OLD_CRETAN_DORIC_ALT_RTL (alternate, right to left)
>
> and this, or more, for perhaps 10 different archaic Greek scripts...
err, I
> mean dialects.
>
> That probably isn't something that could/should end up on Microsoft's
official
> language list.
Setting aside questions of what should end up in the OpenType registry
of OT language-system tags, let me focus on what technology mechanisms
should be applied to the choices you want:
The choice between Old Cretan Doric and the alternate (or 10 other
alternates -- assuming there's agreement that these should be considered
variants of the same script rather than multiple scripts) can be handled
using language-specific rendering; in the case of OpenType, this would
happen with the application specifying a particular OT language-system
tag and then using the 'locl' feature under that language system to
select the necessary alternate glyphs. (This substitution should happen
at the start of GSUB processing.) Other options are to use stylistic set
features or 'aalt' (to select alternate glyphs one character at a time).
The choice between LTR and RTL requires certain things to be done by the
app and certain things to be done in the font. The app should take care
of selecting the line direction (whether its control mechanism is a
formatting setting or Unicode bidi control characters), and applying
bidi mirroring to mirrored character pairs (per Unicode character
properties). Then, for the RTL runs of text, a feature should be applied
to select RTL variants of glyphs for non-mirror-paired characters. In
OpenType, the 'rtla' feature should be used for this purpose.
Peter Constable
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