[NTG-context] Re: fixing kerning and substitutions

9 Oct 2024

      On 10/9/2024 12:22 PM, Florian Grammel wrote:
...
I am trying to reuse code of a project from 2017 with TL23 context. (Other questions probably coming up...)
Back then I used font handlers to fix some smaller problems in the font, i.e. a wrongly placed small capital and missing kerning for the small caps.
The following code works with context 2017.04.27 01:00 MKIV beta but has stopped having any effect using recent context (2023.05.05 18:36 LMTX).
There are no error messages.
Has the syntax changed? Or is the functionality dropped completely?
I was also wondering why it has never been working to adjust the kerning for the regular letters, e.g. "A" and "V" in the example, neither in 2017 nor today.
Thanks a lot in advance!
Florian.
\definefontfamily     [mainface] [serif] [Palatino Linotype] [oldstyle]
\setupbodyfont [mainface]
%\feature[+][oldstyle]
%\feature[+][kernup]
%works with Context beta from 2017, doesn't work with TL 2023
\directlua{
fonts.handlers.otf.addfeature
  {
     name = "smcp",
     type = "alternate",
     data =
     	{
             ['eth'] = 'Eth.ordn' ,
%            ['k.smcp'] = 'Ķ' ,
         },
  }
}
%works for the smcp with Context beta from 2017, doesn't work for the regular capital letters
%doesn't work at all with Context TL 2023
\directlua
{
  fonts.handlers.otf.addfeature
   {
     name = "kern",
     type = "kern",
     data =
         {
             ["A"] = { ["V"] =  1500 },
             ["P"] = { ["Æ"] =  1500 },
             ["a.smcp"] = { ["s.smcp"] =  1500 },
          },
   }
  }
\startdocument
AVAPÆV
þýðask
{\sc þýðask}
123
Nothing has changed (in fact, the font handler hasn't been touched that 
much at all, apart from some fixes for border cases that you're unlikely 
to run into).

There are several issues with your approach, one being that you add a 
feature *after* defining the font, so it is not applied. You also use 
names and that fonts doesn't have names like that.

Something like this can work:

\startluacode
local getsubstitution = fonts.handlers.otf.getsubstitution

fonts.handlers.otf.addfeature {
     name = "smcp",
     type = "alternate",
     data = {
         ["ð"] = char_e,
     },
     data = function(data,specification,list,i)
         -- maybe intercept this cheat in a next version
         data = { shared = { rawdata = { resources = data.resources } } }
         --
         local char_e = 
getsubstitution(data,utf.byte("ð"),"ordn",1,"latn","dflt")
         return {
             ["ð"] = char_e,
         }
     end,
}

fonts.handlers.otf.addfeature {
     name = "kern",
     type = "kern",
     data = function(data,specification,list,i)
         -- maybe intercept this cheat in a next version
         data = { shared = { rawdata = { resources = data.resources } } }
         --
         local char_a = 
getsubstitution(data,utf.byte("a"),"smcp",1,"latn","dflt")
         local char_s = 
getsubstitution(data,utf.byte("s"),"smcp",1,"latn","dflt")
         return {
             ["A"]    = { ["V"]    = 1500 },
             ["P"]    = { ["Æ"]    = 1500 },
             [char_a] = { [char_s] = 1500 },
         }
     end,
}
\stopluacode

\definefontfamily [mainface] [serif]  [Palatino Linotype]
\definefontfamily [mainface] [math]   [TeX Gyre Pagella]

\setupbodyfont [mainface]

\starttext
     AVAPÆV
     þýðask
     {\smallcaps þýðask}
     123
\stoptext

But it is a kind of ugly solution, mostly demonstrating that the nature 
of tex is that one can always find a solution for any weird problem.

Hans

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