[luatex] How to access user-defined kerning

[Henri Menke]

On Fri, 2018-04-20 at 07:47 +0200, Herbert Voss wrote:
> Am 20.04.2018 um 05:52 schrieb Henri Menke:
> 
> > 
> > I'm trying to determine the kerning between two letters (here A and V).  For
> > the
> > sake of this example I'm inserting negative kerning of -400/1000 em.
> >  However,
> > when I examine the kern in the kerning callback this massive enhancement of
> > the
> > negative kern doesn't show up but I only see the kerning from the font
> > itself.
> > 
> > How can I access the user-defined kerns?  MWE is below.
> no problem with

No, that is not my problem.  The kern is correct in the output.  However, I
cannot inspect the kern from within the "kerning" callback.  The user-defined
kern is not added inside the kerning callback and I want to know how to query it
(see the line annotated with <--).

\input luaotfload.sty

\directlua{
local function show_kerns(head)
   for item in node.traverse(head) do
      if item.id == node.id("glyph") and item.char == 65 then
         % Get current char and font
         local nut = node.direct.todirect(item)
         local char = node.direct.getchar(nut)
         local font = node.direct.getfont(nut)
         print(font) % <-- the kern is wrong here
         % Get next char and font
         local next = node.next(item)
         local nextnut = node.direct.todirect(next)
         local nextchar = node.direct.getchar(nextnut)
         local nextfont = node.direct.getfont(nextnut)
         % Determine the kern
         local data = fonts.hashes.identifiers[font]
         local kern = fonts.handlers.otf.getkern(data,char,nextchar)
         print(kern)
      end
   end
end
%
luatexbase.add_to_callback("kerning",
                           function(head)
                              show_kerns(head)
                              node.kerning(head)
                           end,
                           "show_kerns")
}

\directlua{
fonts.handlers.otf.addfeature{
   name = "ktest",
   type = "kern",
   data = { ["A"] = { ["V"] =  -400 } } % make them overlap for the example
}
}

\font\test="Latin Modern Roman:+ktest"\test
AV

\bye

> 
> \input luaotfload.sty
> 
> \directlua{
>    fonts.handlers.otf.addfeature{
>      name = "ktest",
>      type = "kern",
>      data = {
>        ["A"] = { ["V"] =  -400 } } % make them overlap for the example
>    }
> }
> 
> AV
> 
> \font\test="Latin Modern Roman:+ktest" at 11pt
> \test
> AV
> 
> \bye
> 
> 
> This is LuaTeX, Version 1.07.0 (TeX Live 2018)
> 
> 
> Herbert