Lookup indexes dumped, but not read

It seems like lookup indexed are detemined by order of the lookups in the GSUB table, and not by the actual index in the attribute.

Changing this:

<GSUB>
  ... 
  <FeatureList>
    <!-- FeatureCount=1 -->
    <FeatureRecord index="0">
      <FeatureTag value="ccmp"/>
      <Feature>
        <!-- LookupCount=1 -->
        <LookupListIndex index="0" value="0"/>
      </Feature>
    </FeatureRecord>
  </FeatureList>
  <LookupList>
    <!-- LookupCount=1 -->
    <Lookup index="0">
      ...
    </Lookup>
  </LookupList>
</GSUB>

to this:

<GSUB>
  ... 
  <FeatureList>
    <!-- FeatureCount=1 -->
    <FeatureRecord index="0">
      <FeatureTag value="ccmp"/>
      <Feature>
        <!-- LookupCount=1 -->
        <LookupListIndex index="0" value="999"/>
      </Feature>
    </FeatureRecord>
  </FeatureList>
  <LookupList>
    <!-- LookupCount=1 -->
    <Lookup index="999">
      ...
    </Lookup>
  </LookupList>
</GSUB>

I would expect this to work, or see a comment indicating the indexes are not used when compiling the .ttx back to a font.

[typoman]

I’m not sure if this would help, you can open the font using python and append the lookups to the end of LookupList and change the LookupCount. Then you need to find out how you can reference the lookups based on their index in this list.

from fontTools.ttLib import TTFont
f = TTFont(font_path)
print(f["GSUB"].table.LookupList.Lookup) # the list of lookups

[RoelN]

Agreed, it’d be a nice to have but I imagine resources are best spent on other parts. Thanks for considering this nonetheless!