Re: [NTG-context] disabling specific ligatures

22 Mar 2017

      On 3/21/2017 5:44 PM, Csikos Bela wrote:
...
Dear context users:
Is it possible to disable a specific ligature in a whole document in mkiv?
I would like to disable fi ligature.
Does it make a difference if I use a true type font installed on my
system?
normally that is done by setting a language feature in the font

you can also cook up a new feature, like

     fonts.handlers.otf.addfeature {
         name    = "nofiligature1",
         type    = "chainsubstitution",
         nocheck = true,
         prepend = true,
         lookups = {
             {
                 type = "multiple",
                 data = {
                     ["f"] = { "f", 0x200C },
                  -- ["i"] = { "i" },
                 },
             },
         },
         data = {
             rules = {
                 {
                  -- current = { { "f" }, { "i" } },
                  -- lookups = { 1, 1 },
                     current = { { "f" } },
                     after   = { { "i" } },
                     lookups = { 1 },
                 },
             },
         }
     }

     fonts.handlers.otf.addfeature {
         name    = "nofiligature2",
         type    = "chainsubstitution",
         nocheck = true,
         append  = true,
         lookups = {
             {
                 type = "ligature",
                 data = {
                     ["f"] = { "f", 0x200C },
                 },
             },
          -- {
          --     type = "substitution",
          --     data = {
          --         ["i"] = "i"
          --     },
          -- },
         },
         data = {
             rules = {
                 {
                  -- current = { { "f" }, { 0x200C }, { "i" } },
                  -- lookups = { 1, 2 },
                     current = { { "f" }, { 0x200C } },
                     after   = { { "i" } },
                     lookups = { 1 },
                 },
             },
         }
     }

Here the two step approach is needed to make sure you get proper kerning 
(given that a font has it, e.g pagella has between fe but not between 
ffe so ...).

Anyway, I've added a helper to the upcoming so that it's a bit easier:

\blockligatures[fi,ff]
\blockligatures[fl]

\definefontfeature
   [default]
   [default]
   [blockligatures=yes]

\setupbodyfont[pagella]

The only thing you need to keep in mind is that the \blockligature 
commands have to come before fonts get defined (has to do with shared 
resources and optimizations and such) and of course that you need to
enable the feature.

Hans

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