Enabling stylistic sets (e.g. ss02) with fonttools

Comments

• Connor Davenport Posts: 35

  May 2022 edited May 2022

  You can do this by tweaking the CMAP table in the font. Essentially you just have to set the unicode slot for the default glyph to be assigned to the alternate. 
  
  

  <map code="0x67" name="g.alt"/><!-- LATIN SMALL LETTER G -->

  
  Here is a simple example of how to do this in FontTools too. This is probably very convoluted and not the best way if you want the script to be flexible but it works for this specific example with Recursive. I didn't include it in this example but you can also reverse the dictionary from the ```Subtable.mapping``` to swap the GSUB.
  
  

  import os
  from fontTools.ttLib import TTFont
  
  feasToFreeze = "ss02 ss03 ss04 ss05 ss08 ss11".split(" ")
  path = 'path/to/font.ttf'
  
  ext = os.path.splitext(path)[1]
  savePath = path.replace(ext,f"-frozen.{ext}")
  
  f = TTFont(path)
  
  GSUB = f["GSUB"]
  cmap = f['cmap']
  
  def getUnicodeFromName(name, subtable):
      u = None
      for uni,CIDname in list(subtable.cmap.items()):
          if CIDname == name:
              u = uni
      if u:
          return u
          
  i = []
  for fea in feasToFreeze:
      for r in GSUB.table.FeatureList.FeatureRecord:
          if r.FeatureTag == fea:
              i.append(r.Feature.LookupListIndex[0])
  i = sorted(list(set(i)))
  
  mapping = {}
  if i:
      for LookupID in i:
          Lookup = GSUB.table.LookupList.Lookup[LookupID]
          for Subtable in Lookup.SubTable:
              if Subtable.LookupType == 1:
                  mapping.update(Subtable.mapping)
      if mapping:
          remap = list(mapping.keys())
          for table in cmap.tables: 
              for n in remap:
                  c = getUnicodeFromName(n, table)
                  if c:
                      table.cmap[c] = mapping[n]            
          f.save(savePath)
  

  
  

  1
• Simon Cozens Posts: 724

  May 2022

  Adam's OTF Feature Freezer might do what you want.

  3
• Connor Davenport Posts: 35

  May 2022

  Agreed^ I was just coming back to link that tool:) I originally figured out how to do this because of Adam's code but had tweaked stuff to fit my needs at the time.

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• Casper de With Posts: 4

  May 2022 edited May 2022

  Many thanks for your swift replies! It works!

  +: Oh, only partially, apparently. It doesn’t change ss04 for some weird reason, but it does do the rest. Am I doing something wrong? I tried isolating the problem:
  

  $ pyftfeatfreeze -f 'ss04' Recursive.ttf Recursive-ss04.ttf

  … but it doesn’t change the ‘i’, which it’s supposed to do.

  Connor’s script has the same issue. The problem can’t be the font itself, since I regularly use ss04 without problems in Inkscape. What could it be? Does anyone have a hunch?

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• Connor Davenport Posts: 35

  May 2022 edited May 2022

  @Casper de With I just took a look and it appears that Recursive's ss04 is a type-2 lookup which is a bit more tricky to make work with these tools because type-2 subs are "one for many" so what glyph would we end up swapping for? In the case of Recursive we can just open it and see that there is only one actual type-2 substitution in the feature, so you could just do this all manually and ignore the one that is type-2. 
  
  

  import os
  from fontTools.ttLib import TTFont
  
  path = 'path/to/font.ttf'
  ext = os.path.splitext(path)[1]
  savePath = path.replace(ext,f"-frozen.{ext}")
  
  f = TTFont(path)
  cmap = f['cmap']
  
  def getUnicodeFromName(name, subtable):
      u = None
      for uni,CIDname in list(subtable.cmap.items()):
          if CIDname == name:
              u = uni
      if u:
          return u
  
  sansI = "dotlessi i iacute ibreve icircumflex idieresis idieresisacute idotbelow igrave igravedbl ihook iinvertedbreve imacron iogonek itilde".split(" ")
  smplI = "dotlessi.italic i.simple iacute.simple ibreve.simple icircumflex.simple idieresis.simple idieresisacute.simple idotbelow.simple igrave.simple igravedbl.simple ihook.simple iinvertedbreve.simple imacron.simple iogonek.simple itilde.simple".split(" ")
  
  for i, glyph in enumerate(sansI):
      for table in cmap.tables:
          c = getUnicodeFromName(glyph, table)
          if c:
              table.cmap[c] = smplI[i]
  
  f.save(savePath)
  
  

  
  

  
  

  
  

  3
• Casper de With Posts: 4

  May 2022 edited May 2022

  It works! Thanks for being so helpful, @Connor Davenport!

  +: Thanks for the explanations too – I learnt a lot.
  

  0
• Connor Davenport Posts: 35

  May 2022

  @Casper de With no problem! always happy to help!!

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