Re: [NTG-context] Contextual removal of some ligatures using fonts.handlers.otf.addfeature (LuaTeX 1.13.2)

25 Dec 2021


      On 12/25/2021 12:04 AM, Bruce Horrocks via ntg-context wrote:
...
...
On 24 Dec 2021, at 18:34, Thomas Savary via ntg-context  wrote:
Hello, dear list !
In order to fix a few bugs in some OpenType features included in EB Garamond font provided by Google Fonts, I am trying to remove some ligatures (erroneous in some contexts) with fonts.handlers.otf.addfeature.
I must be missing something, because I can't get it to work.
Here is a minimal —non working—example :-)
(The attempted removal (“f_i” → “fi” only before “o”) is of course irrelevant. I chose it just for the sole purpose of this test, to provide a simple example. What I am trying to achieve is more complex, with other ligatures.)
fonts.handlers.otf.addfeature{
         name = "unfio",
         type = "chainsubstitution",
         lookups = {
             { type = "multiple",
             data = { [ "f_i" ] = { "f", "i" } }
             }
         }
         rules = {
             { after = { { "o" } },
             current = { { "f_i" } },
             lookups = { 1 } }
         }
     }
}
Could someone please explain to me what I did wrong ?
Firstly, you have an extra } in the example above.
Secondly, rules need to come inside a data section. Thus (untested):
fonts.handlers.otf.addfeature{
     name = "unfio",
     type = "chainsubstitution",
     lookups = {
         {
             type = "substitution",
             data = {
                 [ "f_i" ] = { "f", "i" }
             }
         }
     },
     data = {
         rules = {
             {
                 after = { { "o" } },
                 current = { { "f_i" } },
                 lookups = { 1 }
             }
         }
     }
}
A better an dmore reliable approach is this:

\startluacode
     local demo = {
         name    = "demo",
         options = {
             {
                 patterns = {
                     fio  = "f|io",
                 },
                 words = [[ fioot fiots ]],
             },
         },
     }
     table.save("oeps-fixes.llg",demo)
\stopluacode

\setuplanguage[en][goodies={oeps-fixes.llg}]

\setupbodyfont[ebgaramond]

\starttext
     fiets fiots fiats fioot
\stoptext

because you want to block certain ligatures but keep kerning etc (see 
older posts for more extensive examples)

Hans


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