RE: RTL PUA?

From: Peter Constable <petercon_at_microsoft.com>
Date: Sun, 21 Aug 2011 15:56:02 +0000

From: unicode-bounce_at_unicode.org [mailto:unicode-bounce_at_unicode.org] On Behalf Of Philippe Verdy

> Hmmm.... Given the current standard in OpenType, and the fact that
> OpenType fonts cannot reorder glyphs to support the BiDi algorithm
> and correctly handle featues like ligatures...

I agree that OpenType font tables cannot to glyph re-ordering. But totally incorrect in saying that it cannot handle ligatures.

> What this means is that, in practice, PUA are only usable in fonts for
> characters with strong LTR directionality, excluding all reordering and
> mirroring.

In the OpenType specification, the only data related to glyph mirroring that a rendering engine is assumed to have is the bidi mirroring data from TUS 5.1. (See http://www.microsoft.com/typography/otspec/TTOCHAP1.htm#ltrrtl.) All other glyph mirroring is to be handled using glyph substitution data in OpenType Layout tables in fonts.

Peter
Received on Sun Aug 21 2011 - 10:59:33 CDT

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