marseymoji/colrv1_postproc.py

"""
Post-nanoemoji processing of the Noto COLRv1 Emoji file.

For now substantially based on copying from a correct bitmap build.
"""
from absl import app
import functools
from fontTools import ttLib
from fontTools.ttLib.tables import _g_l_y_f as glyf
from fontTools.ttLib.tables import otTables as ot
import map_pua_emoji
from nototools import add_vs_cmap
from nototools import unicode_data
from pathlib import Path


def _is_colrv1(font):
  return (
    "COLR" in font
    and font["COLR"].version == 1
  )


def _is_cbdt(font):
  return "CBDT" in font


def _is_compat_font(font):
  return (
    "meta" in font
    and "Emji" in font["meta"].data
  )


def _copy_emojicompat_data(colr_font, cbdt_font):
    colr_font["meta"] = cbdt_font["meta"]


def _set_name(name_table, nameID):
  name_table.getName(value, nameID, 3, 1, 0x409)


def _set_name(name_table, nameID, value):
  name_table.setName(value, nameID, 3, 1, 0x409)


def _copy_names(colr_font, cbdt_font):
  colr_font["name"] = cbdt_font["name"]
  name_table = colr_font["name"]
  assert all((n.platformID, n.platEncID, n.langID) == (3, 1, 0x409)
             for n in name_table.names), "Should only have names Android uses"

  # Amendments
  _set_name(name_table, 10, "Color emoji font using COLRv1.")
  _set_name(name_table, 11, "https://github.com/googlefonts/noto-emoji")
  _set_name(name_table, 12, "https://github.com/googlefonts/noto-emoji")


# CBDT build step: @$(VS_ADDER) -vs 2640 2642 2695 --dstdir '.' -o "$@-with-pua-varsel" "$@-with-pua"
def _add_vs_cmap(colr_font):
  emoji_variants = unicode_data.get_unicode_emoji_variants() | {0x2640, 0x2642, 0x2695}
  add_vs_cmap.modify_font("COLRv1 Emoji", colr_font, "emoji", emoji_variants)


def _is_variation_selector_cmap_table(table):
  assert table.format in {4, 12, 14}
  return table.format == 14


def _lookup_in_cmap(colr_font, codepoint):
  result = set()
  for table in colr_font["cmap"].tables:
    if _is_variation_selector_cmap_table(table):
      continue
    assert codepoint in table.cmap
    result.add(table.cmap[codepoint])
  assert len(result) == 1, f"Ambiguous mapping for {codepoint}: {result}"
  return next(iter(result))


def _add_cmap_entries(colr_font, codepoint, glyph_name):
  for table in colr_font["cmap"].tables:
    if _is_variation_selector_cmap_table(table):
      continue
    if not _is_bmp(codepoint) and table.format == 4:
      continue
    table.cmap[codepoint] = glyph_name
    print(f"Map 0x{codepoint:04x} to {glyph_name}, format {table.format}")


def _map_missing_flag_tag_chars_to_empty_glyphs(colr_font):
  # Add all tag characters used in flags
  tag_cps = (
    set(range(0xE0030, 0xE0039 + 1))
    | set(range(0xE0061, 0xE007A + 1))
  )

  # Cancel tag
  tag_cps |= {0xE007F}

  # Anything already cmap'd is fine
  tag_cps -= set(_Cmap(colr_font).keys())

  # CBDT maps these to blank glyphs
  glyf_table = colr_font["glyf"]
  hmtx_table = colr_font["hmtx"]
  glyph_order_size = len(glyf_table.glyphOrder)
  for cp in tag_cps:
    print(f"Map 0x{cp:04x} to a blank glyf")
    glyph_name = f"u{cp:04X}"
    assert glyph_name not in glyf_table, f"{glyph_name} already in glyf"
    assert glyph_name not in hmtx_table.metrics, f"{glyph_name} already in hmtx"
    glyf_table[glyph_name] = glyf.Glyph()
    hmtx_table[glyph_name] = (0, 0)

    _add_cmap_entries(colr_font, cp, glyph_name)


def _is_bmp(cp):
  return cp in range(0x0000, 0xFFFF + 1)


def _ligaset_for_glyph(lookup_list, glyph_name):
  for lookup in lookup_list.Lookup:
    if lookup.LookupType != 4:
      continue
    for liga_set in lookup.SubTable:
      if glyph_name in liga_set.ligatures:
        return liga_set.ligatures[glyph_name]
  return None


def _Cmap(ttfont):

  def _Reducer(acc, u):
    acc.update(u)
    return acc

  unicode_cmaps = (t.cmap for t in ttfont['cmap'].tables if t.isUnicode())
  return functools.reduce(_Reducer, unicode_cmaps, {})


def _map_empty_flag_tag_to_black_flag(colr_font):
  # fontchain_lint wants direct support for empty flag tags
  # so map them to the default flag to match cbdt behavior

  # if the emoji font starts using extensions this code will require revision

  cmap = _Cmap(colr_font)
  black_flag_glyph = cmap[0x1f3f4]
  cancel_tag_glyph = cmap[0xe007f]
  lookup_list = colr_font["GSUB"].table.LookupList
  liga_set = _ligaset_for_glyph(lookup_list, black_flag_glyph)
  assert liga_set is not None, "There should be existing ligatures using black flag"

  # Map black flag + cancel tag to just black flag
  # Since this is the ligature set for black flag, component is just cancel tag
  # Since we only have one component its safe to put our rule at the front
  liga = ot.Ligature()
  liga.Component = [cancel_tag_glyph]
  liga.LigGlyph = black_flag_glyph
  liga_set.insert(0, liga)


def main(argv):
    if len(argv) != 3:
      raise ValueError("Must have two args, a COLRv1 font and a CBDT emojicompat font")

    colr_file = Path(argv[1])
    assert colr_file.is_file()
    colr_font = ttLib.TTFont(colr_file)
    if not _is_colrv1(colr_font):
      raise ValueError("First arg must be a COLRv1 font")

    cbdt_file = Path(argv[2])
    assert cbdt_file.is_file()
    cbdt_font = ttLib.TTFont(cbdt_file)
    if not _is_cbdt(cbdt_font) or not _is_compat_font(cbdt_font):
      raise ValueError("Second arg must be a CBDT emojicompat font")

    print(f"COLR {colr_file.absolute()}")
    print(f"CBDT {cbdt_file.absolute()}")

    _copy_emojicompat_data(colr_font, cbdt_font)
    _copy_names(colr_font, cbdt_font)

    # CBDT build step: @$(PYTHON) $(PUA_ADDER) "$@" "$@-with-pua"
    map_pua_emoji.add_pua_cmap_to_font(colr_font)

    _add_vs_cmap(colr_font)

    _map_missing_flag_tag_chars_to_empty_glyphs(colr_font)

    _map_empty_flag_tag_to_black_flag(colr_font)

    out_file = Path('fonts/Noto-COLRv1-noflags.ttf').absolute()
    print("Writing", out_file)
    colr_font.save(out_file)


if __name__ == "__main__":
    app.run(main)