[NTG-context] error calling font.getfont() on certain fonts

Philipp Gesang Philipp.Gesang at alumni.uni-heidelberg.de
Fri Mar 29 16:29:15 CET 2013

···<date: 2013-03-29, Friday>···<from: Hans Hagen>···

> On 3/28/2013 6:41 PM, Philipp Gesang wrote:
> >Hi all,
> >
> >I get an error when I run this code:
> >
> >     \ctxlua{font.getfont( font.current() )}
> >
> >(Complete example below.) Oddly, whether or not this fails
> >depends on the font. The issue does occur with both today’s beta
> >and Tex Live. The error message is
> >
> >     error: .../context/tex/texmf-context/tex/context/base/node-inj.lua:97: attempt to perform arithmetic on local 'factor' (a nil value)
> >
> >At the same time, in Plain the equivalent code works fine for all
> >fonts. Bug or feature?
> it's a side effect ... it looks like font.getfont operates on the
> table passed to tex and when you request it it probably fills in
> some data (like parameters) thereby overloading / wiping out
> existing stuff so after that call the data structure as context uses
> (and needs) it is messed up

I just read that in the manual:

  Note that at the moment, each access to the font.fonts or call
  to font.getfont creates a lua table for the whole font. This
  process can be quite slow. In a later version of LuaTEX, this
  interface will change (it will start using userdata objects
  instead of actual tables).

> add this after the definition of
> definers.read(specification,size,id) and it will probably work ok
> function font.getfont(id)
>     return fontdata[id] -- otherwise issues
> end
> (I'll add a similar overload someplace else.)

Great! Looking forward to the next update.

> in context you can try this:
> \startluacode
>     function font.getfont(id)
>         return fonts.hashes.identifiers[id]
>     end
> \stopluacode
> \starttext
>   foo
>   \ctxlua{inspect(font.getfont( font.current()).parameters )}
>   bar
> \stoptext
> if you comment the function overload you see the difference

Compared to Plain, Context adds a lot to the “.parameters” table. 
Sadly, writing to it doesn’t appear to change anything …


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