[luatex] information about ligatures

[Philipp Gesang]

···<date: 2014-01-06, Monday>···<from: Stephan Hennig>···

> Am 05.01.2014 19:03, schrieb Philipp Gesang:
> > 
> > It depends on whether the “liga” feature is active and whether
> > you use base mode or node mode.
> 
> Well, let me add a related question.  To quote from the luaotfload manual:
> 
> > node mode works by processing TeX's internal node list directly at
> > the Lua end
> 
> What callback does luaotfload use for the processing?

The font handler is applied to both the pre_linebreak_filter and
the hpack_filter.

https://github.com/phi-gamma/luaotfload/blob/texlive2014/luaotfload.dtx#L1919

>                                                        And what is the
> way to go for packages fighting for a callback?

luatexbase.add_to_callback() without priority (append).

>                                                  If callbacks are "just
> chained", how can I be sure that luaotfload has already done its
> processing before my package?

Luaotfload inserts the callbacks into the chain at highest
priority. As long as you do not specify a priority, you should be
fine.

> > E.g. in Context: [...] The values are:
> > 
> >       mode | liga
> >            |  -     +
> >       -----+--------
> >       base | 256     2
> >       node | 256   258
> > 
> > Run this with the bare fontloader, you get
> > 
> >       mode | liga
> >            |  -     +
> >       -----+--------
> >       base | 256     2
> >       node | 256   256
> > 
> > With luaotfload, however, it’s
> > 
> >       mode | liga
> >            |  -     +
> >       -----+--------
> >       base | 256   258
> >       node | 256   256
> 
> OK, what does that teach me?

That you should be able to call the inverse operation
(node.unprotect_glyphs()) on the node list to restore the
original values.

>                               I think I'll just look at (and follow) the
> components field to parse ligatures and hope for the best ...

I came up with this heuristic:
http://tex.stackexchange.com/a/120529/14066

Best,
Philipp


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