[luatex] What are user-defined whatsit nodes?

Hans Hagen pragma at wxs.nl
Mon Nov 24 00:38:19 CET 2014

On 11/23/2014 11:49 PM, Stephan Hennig wrote:
> Am 23.11.2014 um 19:43 schrieb Hans Hagen:
>> you can just reconstruct the original from the (nested) ligatures,
> I have experimented with code like that.  The problem is that triple
> ligatures can be broken in two ways:
>    ffl   =>
>               ff + l  Leuchtstofflampe (fluorescent lamp)
>               f + fl  Tiefflieger (low-level attack aircraft)
> The former case is easy, since components of the ffl ligature are glyphs
> 'ff' and 'l'.  The second case requires to compose the fl ligature from
> raw font information, since it is not readily available.  Effectively,
> this means implementing a full ligaturing routine.  I wouldn't want to
> do that.  Is there any interface available that given two glyphs returns
> a ligature of those glyphs?

that's not the way open type works ... some fonts can turn ffl into the 
ffl ligature, others do it stepwise and yet others implement for 
instance ff ligatures by kerning two (different) f's, in fact the whole 
concept of ligature in open type is a kind of generic substitution and 
does not always relate to ligatures .. the feature can be mixed into 
other features as well

                                           Hans Hagen | PRAGMA ADE
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