From: Philippe Verdy <>
Date: Sun, 21 Aug 2011 21:16:05 +0200

2011/8/21 Peter Constable <>:
>> Exactly, but mirroring data for remapping glyphs will not be be part of that
>> font.
> Um... Why not? If the mirroring isn't in reflected in, then it must be handled by glyph substitution in the font as a normal GSUB operation.

A GSUB operation will only be used if it is specified in the correct
feature table. The problem here is which feature to use: "rtlm" or
"ltrm" ? It's impossible to know because it first depend on the layout
engine to KNOW exactly if the run of text is RTL or LTR.

Without a font-level support of BiDi properties of PUAs (or unassigned
characters), the layout engine will assume the wrong guess from the
"default" property value. And then it won't find the expected GSUB
operation, because it won't match it in the correct feature subtable.
Received on Sun Aug 21 2011 - 14:18:54 CDT

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