[XeTeX] Θέμα: Re: OpenType ligatures

Adam Twardoch list.adam at twardoch.com
Fri Nov 24 20:33:44 CET 2006

Alexej Kryukov wrote:
 > Unfortunately this also means that the way XeTeX handles OT fonts
 > has a really serious limitation. Many OT rules may depend from
 > spaces found in the input stream, and, of course, typing spaces
 > as \char 32 is not an option in this case.

XeTeX is not alone. Many applications paint interword whitespace without 
using the font-specific space glyph. Also, many OpenType Layout engines 
including the reference implementation (Uniscribe) split text into runs 
by using the space character as the separator, and apply OpenType Layout 
features only within the runs -- excluding the space characters. In 
other words, defining OpenType Layout behaviors that depend on the space 
glyph is risky -- there is absolutely no guarantee that this will work 
in all engines.

The way XeTeX works is perfectly fine and I don't think this really 
needs to be changed. It is possible to implement contextual features 
like the one in the sample font without relying on the space glyph.

BTW, the recommended implementation of the hist feature is using GSUB 
LookupType 1, not LookupType 5 or 6.


Adam Twardoch
| Language Typography Unicode Fonts OpenType
| twardoch.com | silesian.com | fontlab.net

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