JSTF Table builder

JSTFBuilder.py

#!/usr/bin/env python
# Builds a JSTF table from specially named features
# To use:
# First, set up the features in your font.
# You may add as many or as few features as you like, but they must conform
# to the following naming convention:
#    exs1: First priority extension substitution.
#     i.e. the first rules we try to substitute glyphs to make the line longer
#    exp1: First priority extension positioning.
#     i.e. the first rules we try to reposition glyphs to make the line longer
#    shs1: First priority shrinkage substitution.
#     i.e. the first rules we try to substitute glyphs to make the line shorter
#    exp1: First priority shrinkage positioning.
#     i.e. the first rules we try to reposition glyphs to make the line shorter

# If you want to specify a second level of suggestions to the layout engine,
# add one or more features called exs2, exp2, shs2, or shp2.

# For example: to tell the layout engine that, if it wants a longer line, it can
# try replacing H by H.wide and/or O by O.wide, add a feature:
#    feature exs1 {
#      sub H by H.wide;
#      sub O by O.wide
#    } exs1;

# To tell the layout engine that, if it *still* wants a longer line, it should next
# try replacing G by G.wide, add a feature:
#    feature exs2 {
#      sub G by G.wide;
#    } exs2;

# Next run this script on your font. Expected output:
# % python3 jstf-builder.py JSTFSans-Regular.otf
# Looking for suggestion 1...
# Found extension substitution feature exs1 (lookups=0)
# Found shrinkage substitution feature shs1 (lookups=2)

# Looking for suggestion 2...
# Found extension substitution feature exs2 (lookups=1)
# Found shrinkage substitution feature shs2 (lookups=3)

# Looking for suggestion 3...
# Not found, ending here
# Saving JSTF-JSTFSans-Regular.otf

import argparse

from fontTools.ttLib import TTFont
from fontTools.misc.py23 import *
from fontTools import ttLib
import sys
from fontTools.ttLib.tables import otTables as ot
from collections import OrderedDict

from argparse import ArgumentParser

parser = ArgumentParser()
parser.add_argument("input",
                    help="font file to process", metavar="FILE")
parser.add_argument("--extender", dest="extenders", action='append',
                    help="Glyph names which act as extenders (tatweels, etc.)")
parser.add_argument("-o", dest="output",
                    help="path to output font", metavar="FILE")

args = parser.parse_args()
extenderGlyphs = args.extenders
fontPath = args.input
output = args.output
if output is None:
  output = "JSTF-"+args.input

font = TTFont(fontPath)

tag = Tag("JSTF")
jstfTable = ttLib.getTableClass(tag)(tag)
tableClass = getattr(ot, tag)
jstfTable.table = tableClass()
jstfTable.table.populateDefaults()
setattr(jstfTable.table, "Version", 0x00010000)

# For now, everything lives in DFLT/dflt
rec =  ot.JstfScriptRecord()
setattr(rec, "JstfScriptTag", "DFLT")
script =  ot.JstfScript()

extender = ot.ExtenderGlyph()
setattr(extender, "ExtenderGlyph", extenderGlyphs)
setattr(script, "ExtenderGlyph", extender)

deflang = ot.DefJstfLangSys()
setattr(script, "DefJstfLangSys", deflang)


# Gather GSUB stuff
gsubfeatures = OrderedDict()
gposfeatures = OrderedDict()
def _prepareFeatureLangSys(langTag, langSys, table, features, scriptTag):
    # This is a part of prepareFeatures
    for featureIdx in langSys.FeatureIndex:
        featureRecord = table.FeatureList.FeatureRecord[featureIdx]
        featureTag = featureRecord.FeatureTag
        scripts = features.get(featureTag, None)
        if scripts is None:
            scripts = OrderedDict()
            features[featureTag] = scripts

        languages = scripts.get(scriptTag, None)
        if languages is None:
            languages = OrderedDict()
            scripts[scriptTag] = languages

        lookups = languages.get(langTag, None)
        if lookups is None:
            lookups = []
            languages[langTag] = lookups

        for lookupIdx in featureRecord.Feature.LookupListIndex:
            lookups.append(lookupIdx)

for scriptRecord in font["GSUB"].table.ScriptList.ScriptRecord:
    scriptTag = scriptRecord.ScriptTag
    if scriptRecord.Script.DefaultLangSys is not None:
        _prepareFeatureLangSys('dflt', scriptRecord.Script.DefaultLangSys, font["GSUB"].table, gsubfeatures, scriptTag)
    for langSysRecord in scriptRecord.Script.LangSysRecord:
        _prepareFeatureLangSys(langSysRecord.LangSysTag, langSysRecord.LangSys, font["GSUB"].table, gsubfeatures, scriptTag)

for scriptRecord in font["GPOS"].table.ScriptList.ScriptRecord:
    scriptTag = scriptRecord.ScriptTag
    if scriptRecord.Script.DefaultLangSys is not None:
        _prepareFeatureLangSys('dflt', scriptRecord.Script.DefaultLangSys, font["GPOS"].table, gposfeatures, scriptTag)
    for langSysRecord in scriptRecord.Script.LangSysRecord:
        _prepareFeatureLangSys(langSysRecord.LangSysTag, langSysRecord.LangSys, font["GPOS"].table, gposfeatures, scriptTag)

suggestion = 0

while True:
  foundAny = False
  suggestion = suggestion + 1
  if suggestion > 10:
    raise ValueError("More than 10 suggestions not supported")
  print("\nLooking for suggestion %i..." % suggestion)
  thisSuggestion = ot.JstfPriority()
  if ("exs%1i" % suggestion) in gsubfeatures:
    foundAny = True
    lookups = gsubfeatures["exs%1i" % suggestion]["DFLT"]["dflt"]
    print("Found extension substitution feature exs%i (lookups=%s)" % (suggestion, ",".join([str(x) for x in lookups])))
    ext = ot.ExtensionEnableGSUB()
    setattr(ext, "GSUBLookupIndex",lookups)
    setattr(thisSuggestion, "ExtensionEnableGSUB", ext)

  if ("exp%1i" % suggestion) in gposfeatures:
    foundAny = True
    lookups = gposfeatures["exs%1i" % suggestion]["DFLT"]["dflt"]
    print("Found extension positioning feature exp%i (lookups=%s)" % (suggestion, ",".join([str(x) for x in lookups])))
    ext = ot.ExtensionEnableGPOS()
    setattr(ext, "GPOSLookupIndex",lookups)
    setattr(thisSuggestion, "ExtensionEnableGPOS", ext)

  if ("shs%1i" % suggestion) in gsubfeatures:
    foundAny = True
    lookups = gsubfeatures["shs%1i" % suggestion]["DFLT"]["dflt"]
    print("Found shrinkage substitution feature shs%i (lookups=%s)" % (suggestion, ",".join([str(x) for x in lookups])))
    ext = ot.ShrinkageEnableGSUB()
    setattr(ext, "GSUBLookupIndex",lookups)
    setattr(thisSuggestion, "ShrinkageEnableGSUB", ext)

  if ("shp%1i" % suggestion) in gposfeatures:
    foundAny = True
    lookups = gposfeatures["shs%1i" % suggestion]["DFLT"]["dflt"]
    print("Found shrinkage positioning feature shp%i (lookups=%s)" % (suggestion, ",".join([str(x) for x in lookups])))
    ext = ot.ShrinkageEnableGPOS()
    setattr(ext, "GPOSLookupIndex",lookups)
    setattr(thisSuggestion, "ShrinkageEnableGPOS", ext)

  if not foundAny:
    print("Not found, ending here")
    break
  if not (hasattr(deflang,"JstfPriority")):
    setattr(deflang, "JstfPriority", [])
  newList = getattr(deflang,"JstfPriority") + [thisSuggestion]
  setattr(deflang, "JstfPriority", getattr(deflang,"JstfPriority") + [thisSuggestion])

setattr(rec, "JstfScript", script)

jstfTable.table.JstfScriptRecord.append(rec)

font["JSTF"] = jstfTable

print("Saving "+output)
font.save(output)