Re: RTL PUA?

From: John Hudson <john_at_tiro.ca>
Date: Tue, 23 Aug 2011 10:02:29 -0700

Philippe Verdy <verdy_p_at_wanadoo.fr> wrote:

>> The computing order of features should not then be:
>> - BiDi algorithm for reordering grapheme clusters
>> - font search and font fallback (using cmap)
>> - GSUB (lookups of ligatures or discretionary glyph variants)
>> - GPOS

>> but really:

>> - font lookup and font fallback (using cmap)
>> - GSUB (lookups of ligatures or discretionary glyph variants)
>> - BiDi algorithm for reordering glyphs representing the grapheme
>> clusters or ligatured grapheme clusters
>> - GPOS

I can see the advantages of such an approach -- performing GSUB prior to
BiDi would enable cross-directional contextual substitutions, which are
currently impossible -- but the existing model in which BiDi is applied
to characters *not glyphs* isn't likely to change. Switching from
processing GSUB lookups in logical order rather than reading order would
break too many things.

JH

-- 
Tiro Typeworks        www.tiro.com
Gulf Islands, BC      tiro_at_tiro.com
The criminologist's definition of 'public order
crimes' comes perilously close to the historian's
description of 'working-class leisure-time activity.'
  - Sidney Harring, _Policing a Class Society_
Received on Tue Aug 23 2011 - 12:09:09 CDT

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