Re: Contextual removal of some ligatures using fonts.handlers.otf.addfeature (LuaTeX 1.13.2)

[Hans Hagen via ntg-context <ntg-context@ntg.nl>]

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 <ntg-context@ntg.nl> 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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