inter/misc/tools/fix-vf-meta.py

#!/usr/bin/env python
#
# from gftools
# https://github.com/googlefonts/gftools/blob/
# deebf9eb018856ffc7f0d939aea18606dc432c5a/bin/gftools-fix-vf-meta.py
#
"""
Fontmake can only generate a single variable font. It cannot generate a
family of variable fonts, that are related to one another.

This script will update the nametables and STAT tables so a family
which has more than one variable font will work correctly in desktop
applications.

It will also work on single font VF families by creating a better STAT
table.

TODO make script work on VFs which have multiple axises. We'll need to
change the axis array format to v4 (we're using v1),
https://docs.microsoft.com/en-us/typography/opentype/spec/stat#axis-value-table-format-4

Atm, the script will work well for single axis fonts and families which
have a single vf for Roman and another for Italic/Condensed, both using the wght
axis (covers 95% of GF cases).
"""
from argparse import ArgumentParser
from fontTools.ttLib import TTFont, newTable
from fontTools.ttLib.tables import otTables
import os
import sys
if sys.version_info.major == 3:
  unicode = str

OS_2_WEIGHT_CLASS = {
  'Thin': 100,
  'ExtraLight': 200,
  'Light': 300,
  'Regular': 400,
  '': 400,
  'Medium': 500,
  'SemiBold': 600,
  'Bold': 700,
  'ExtraBold': 800,
  'Black': 900,
}


def _parse_styles(stylename):
  bold, italic = False, False
  if 'Italic' in stylename:
    italic = True
    bold = False
  if 'Bold' == stylename or 'Bold Italic' == stylename:
    bold = True
  return bold, italic


def set_fsselection(style, fsselection,):
  bold, italic = _parse_styles(style)

  mask = 0b1100001
  fsselection = (fsselection | mask) ^ mask

  if bold:
    fsselection |= 0b100000
  else:
    fsselection |= 0b1000000
  if italic:
    # unset Reg bit
    fsselection = (fsselection | 0b1000000) ^ 0b1000000
    fsselection |= 0b1
  return fsselection


def set_mac_style(stylename, macstyle):
  bold, italic = _parse_styles(stylename)

  mask = ~0b11
  bold_bit = 0b1 if bold else 0b0
  italic_bit = 0b10 if italic else 0b0

  macstyle = (macstyle | mask) ^ mask
  macstyle |= (bold_bit + italic_bit)
  return macstyle


def set_weight_class(stylename):
  weight = stylename.replace('Italic', '').replace(' ', '')
  return OS_2_WEIGHT_CLASS[weight]


def fonts_are_same_family(ttfonts):
  """Check fonts have the same preferred family name or family name"""
  family_names = []
  for ttfont in ttfonts:
    pref_family_name = ttfont['name'].getName(16, 3, 1, 1033)
    family_name = ttfont['name'].getName(1, 3, 1, 1033)
    name = pref_family_name if pref_family_name else family_name
    family_names.append(name.toUnicode())
  if len(set(family_names)) != 1:
    return False
  return True


def fix_bits(ttfont):
  """Set fsSelection, macStyle and usWeightClass to correct values.

  The values must be derived from the default style. By default, the
  Regular instance's values are used"""
  dflt_style = _get_vf_default_style(ttfont)
  ttfont['OS/2'].fsSelection = set_fsselection(
    dflt_style, ttfont['OS/2'].fsSelection
  )
  ttfont['OS/2'].usWeightClass = set_weight_class(dflt_style)
  ttfont['head'].macStyle = set_mac_style(
    dflt_style, ttfont['head'].macStyle
  )


def create_stat_table(ttfont):
  """Atm, Fontmake is only able to produce a basic stat table. Because of
  this, we'll create a STAT using the font's fvar table."""
  stat = newTable('STAT')
  stat.table = otTables.STAT()
  stat.table.Version = 0x00010001

  # # Build DesignAxisRecords from fvar
  stat.table.DesignAxisRecord = otTables.AxisRecordArray()
  stat.table.DesignAxisRecord.Axis = []

  stat_axises = stat.table.DesignAxisRecord.Axis

  # TODO (M Foley) add support for fonts which have multiple
  # axises e.g Barlow
  if len(ttfont['fvar'].axes) > 1:
    raise Exception('VFs with more than one axis are currently '
            'not supported.')

  for idx, axis in enumerate(ttfont['fvar'].axes):
    append_stat_axis(stat, axis.axisTag, axis.axisNameID)

  # Build AxisValueArrays for each namedInstance from fvar namedInstances
  stat.table.AxisValueArray = otTables.AxisValueArray()
  stat.table.AxisValueArray.AxisValue = []

  for idx, instance in enumerate(ttfont['fvar'].instances):
    append_stat_record(stat, 0, list(instance.coordinates.values())[0], instance.subfamilyNameID)

  # Set ElidedFallbackNameID
  stat.table.ElidedFallbackNameID = 2
  ttfont['STAT'] = stat


def _get_vf_types(ttfonts):
  styles = []
  for ttfont in ttfonts:
    styles.append(_get_vf_type(ttfont))
  return styles


def _get_vf_type(ttfont):
  style = ttfont['name'].getName(2, 3, 1, 1033).toUnicode()
  return 'Italic' if 'Italic' in style else 'Roman'


def _get_vf_default_style(ttfont):
  """Return the name record string of the default style"""
  default_fvar_val = ttfont['fvar'].axes[0].defaultValue

  name_id = None
  for inst in ttfont['fvar'].instances:
    if inst.coordinates['wght'] == default_fvar_val:
      name_id = inst.subfamilyNameID
  return ttfont['name'].getName(name_id, 3, 1, 1033).toUnicode()


def add_other_vf_styles_to_nametable(ttfont, text_records):
  """Each nametable in a font must reference every font in the family.
  Since fontmake doesn't append the other families to the nametable,
  we'll do this ourselves. Skip this step if these records already
  exist."""
  found = set()
  for name in ttfont['name'].names[:-len(text_records)-1:-1]:
    found.add(name.toUnicode())
  leftover = set(text_records) - found

  if leftover:
    nameid = ttfont['name'].names[-1].nameID + 1
    for record in leftover:
      ttfont['name'].setName(unicode(record), nameid, 3, 1, 1033)
      nameid += 1


def get_custom_name_record(ttfont, text):
  """Return a name record by text. Record ID must be greater than 255"""
  for record in ttfont['name'].names[::-1]:
    if record.nameID > 255:
      rec_text = record.toUnicode()
      if rec_text == text:
        return record
  return None


def append_stat_axis(stat, tag, namerecord_id):
  """Add a STAT axis if the tag does not exist already."""
  has_tags = []
  axises = stat.table.DesignAxisRecord.Axis
  for axis in axises:
    has_tags.append(axis.AxisTag)

  if tag in has_tags:
    raise Exception('{} has already been declared in the STAT table')

  axis_record = otTables.AxisRecord()
  axis_record.AxisTag = tag
  axis_record.AxisNameID = namerecord_id
  axis_record.AxisOrdering = len(axises)
  axises.append(axis_record)


def append_stat_record(stat, axis_index, value, namerecord_id, linked_value=None):
  records = stat.table.AxisValueArray.AxisValue
  axis_record = otTables.AxisValue()
  axis_record.Format = 1
  axis_record.ValueNameID = namerecord_id
  axis_record.Value = value
  axis_record.AxisIndex = axis_index

  axis_record.Flags = 0
  if linked_value:
    axis_record.Format = 3
    axis_record.LinkedValue = linked_value
  records.append(axis_record)


def get_stat_axis_index(ttfont, axis_name):
  axises = ttfont['STAT'].table.DesignAxisRecord.Axis
  available_axises = [a.AxisTag for a in axises]
  for idx, axis in enumerate(axises):
    if axis.AxisTag == axis_name:
      return idx
  raise Exception('{} is not a valid axis. Font has [{}] axises'.format(
    axis_name, available_axises)
  )


def set_stat_for_font_in_family(ttfont, family_styles):
  """Based on examples from:
  https://docs.microsoft.com/en-us/typography/opentype/spec/stat"""
  font_type = _get_vf_type(ttfont)
  # See example 5
  if font_type == 'Roman' and 'Italic' in family_styles:
    name_record = get_custom_name_record(ttfont, 'Italic')
    append_stat_axis(ttfont['STAT'], 'ital', name_record.nameID)

    name_record = get_custom_name_record(ttfont, 'Roman')
    axis_idx = get_stat_axis_index(ttfont, 'ital')
    append_stat_record(ttfont['STAT'], axis_idx, 0, name_record.nameID, linked_value=1.0)

  elif font_type == 'Italic' and 'Roman' in family_styles:
    name_record = get_custom_name_record(ttfont, 'Italic')
    append_stat_axis(ttfont['STAT'], 'ital', name_record.nameID)

    name_record = get_custom_name_record(ttfont, 'Italic')
    axis_idx = get_stat_axis_index(ttfont, 'ital')
    append_stat_record(ttfont['STAT'], axis_idx, 1.0, name_record.nameID)


def harmonize_vf_families(ttfonts):
  """Make sure the fonts which are part of a vf family reference each other
  in both the nametable and STAT table. For examples see:
  https://docs.microsoft.com/en-us/typography/opentype/spec/stat

  """
  family_styles = _get_vf_types(ttfonts)
  for ttfont in ttfonts:
    add_other_vf_styles_to_nametable(ttfont, family_styles)
    set_stat_for_font_in_family(ttfont, family_styles)


def main():
  parser = ArgumentParser()
  parser.add_argument('fonts', nargs='+',
            help='All fonts within a font family must be included')
  args = parser.parse_args()
  font_paths = args.fonts
  ttfonts = [TTFont(p) for p in font_paths]
  if not fonts_are_same_family(ttfonts):
    raise Exception('Fonts have different family_names: [{}]'.format(
      ', '.join(map(os.path.basename, font_paths))
    ))

  for ttfont in ttfonts:
    fix_bits(ttfont)
    create_stat_table(ttfont)
  harmonize_vf_families(ttfonts)

  for path, ttfont in zip(font_paths, ttfonts):
    ttfont.save(path)

if __name__ == '__main__':
  main()