Add cmap format 4 3/1 table for Windows compatibility

Makefile

@@ -204,7 +204,7 @@ $(EMOJI).tmpl.ttx: $(EMOJI).tmpl.ttx.tmpl $(ADD_GLYPHS) $(ALL_COMPRESSED_FILES)
 	$(PYTHON) $(ADD_GLYPHS) -f "$<" -o "$@" -d "$(COMPRESSED_DIR)" $(ADD_GLYPHS_FLAGS)
 
 $(EMOJI_WINDOWS).tmpl.ttx: $(EMOJI_WINDOWS).tmpl.ttx.tmpl $(ADD_GLYPHS) $(ALL_COMPRESSED_FILES)
-	$(PYTHON) $(ADD_GLYPHS) -f "$<" -o "$@" -d "$(COMPRESSED_DIR)" $(ADD_GLYPHS_FLAGS)
+	$(PYTHON) $(ADD_GLYPHS) --add_cmap4 -f "$<" -o "$@" -d "$(COMPRESSED_DIR)" $(ADD_GLYPHS_FLAGS)
 
 %.ttf: %.ttx
 	@rm -f "$@"

add_glyphs.py

@@ -339,14 +339,33 @@ def add_ligature_sequences(font, seqs, aliases):
     for seq, name in pairs:
       add_ligature(lookup, cmap, seq, name)
 
+def add_cmap_format_4(font):
+  """Add cmap format 4 table for Windows support, based on the
+  format 12 cmap."""
 
-def update_font_data(font, seq_to_advance, vadvance, aliases):
+  cmap = get_font_cmap(font)
+
+  newtable = CmapSubtable.newSubtable(4)
+  newtable.platformID = 3
+  newtable.platEncID = 1
+  newtable.language = 0
+  newtable.cmap = {}
+
+  # Format 4 only has unicode values 0x0000 to 0xFFFF
+  for cp, name in cmap.items():
+    if cp < 65535:
+      newtable.cmap[cp] = name
+
+  font['cmap'].tables.append(newtable)
+
+def update_font_data(font, seq_to_advance, vadvance, aliases, add_cmap4):
   """Update the font's cmap, hmtx, GSUB, and GlyphOrder tables."""
   seqs = get_all_seqs(font, seq_to_advance)
   add_glyph_data(font, seqs, seq_to_advance, vadvance)
   add_aliases_to_cmap(font, aliases)
   add_ligature_sequences(font, seqs, aliases)
-
+  if(add_cmap4):
+    add_cmap_format_4(font)
 
 def apply_aliases(seq_dict, aliases):
   """Aliases is a mapping from sequence to replacement sequence.  We can use
@@ -362,7 +381,7 @@ def apply_aliases(seq_dict, aliases):
   return usable_aliases
 
 
-def update_ttx(in_file, out_file, image_dirs, prefix, ext, aliases_file):
+def update_ttx(in_file, out_file, image_dirs, prefix, ext, aliases_file, add_cmap4):
   if ext != '.png':
     raise Exception('extension "%s" not supported' % ext)
 
@@ -386,7 +405,7 @@ def update_ttx(in_file, out_file, image_dirs, prefix, ext, aliases_file):
 
   vadvance = font['vhea'].advanceHeightMax if 'vhea' in font else lineheight
 
-  update_font_data(font, seq_to_advance, vadvance, aliases)
+  update_font_data(font, seq_to_advance, vadvance, aliases, add_cmap4)
 
   font.saveXML(out_file)
 
@@ -409,11 +428,13 @@ def main():
   parser.add_argument(
       '-a', '--aliases', help='process alias table', const='emoji_aliases.txt',
       nargs='?', metavar='file')
+  parser.add_argument(
+      '--add_cmap4', help='add cmap format 4', dest='add_cmap4', action='store_true')
   args = parser.parse_args()
 
   update_ttx(
       args.in_file, args.out_file, args.image_dirs, args.prefix, args.ext,
-      args.aliases)
+      args.aliases, args.add_cmap4)
 
 
 if __name__ == '__main__':