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Re: ligature formation across text chunks

From: Cameron McCormack <cam@mcc.id.au>
Date: Fri, 20 May 2011 09:44:34 +1200
To: Glenn Adams <glenn@skynav.com>
Cc: Tavmjong Bah <tavmjong@free.fr>, Vincent Hardy <vhardy@adobe.com>, "public-svg-wg@w3.org" <public-svg-wg@w3.org>
Message-ID: <20110519214434.GB8399@wok.mcc.id.au>
Glenn Adams:
> I notice the following text in [1] which you cite below:

Tavmjong Bah:
> > Non-Latin alphabet perspective:
> 
> > An expert should be consulted to determine if ligature use is
> > mandatory in some cases. Recall that 10.7.1 blocks ligature usage
> > in some cases. Arabic and Hindi scripts may require ligatures, but
> > at the same time they probably don't allow characters to be moved
> > arbitrarily around.
> 
> The answer about Arabic, Devanagari (as used by Hindi), and other Indic
> scripts is that they DO indeed require mandatory use of a wide variety of
> ligatures and other forms of complex character to glyph mapping, such as:
...

As far as I can tell, the only situations according to the spec where
ligature formation is required not to happen are:

  * When you have multiple text chunks due to x="" etc.

  * When you have non-default values for ‘kerning’ and ‘letter-spacing’.

The first case will probably go away with my text layout proposal.  For
letter-spacing, css3-text says:

  This property specifies the minimum, maximum, and optimal spacing
  between grapheme clusters.

and does not mention ligatures.  It sounds like for compatibility with
CSS text layout we should not disable ligaures with letter-spacing.

css3-text has a font-kerning property, which is similar to our kerning
property, but which doesn’t take lengths: it only has values auto,
normal and none.  Ligature formation is not mentioned in that property’s
definition, either.

-- 
Cameron McCormack ≝ http://mcc.id.au/
Received on Thursday, 19 May 2011 21:45:12 GMT

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