Improve flag support.

This adds some additional flags to the default set.  In addition,
it contains code that creates ligatures for some flag sequences to
others, for a few cases where we want different regions to share
the same flag.  Finally, it adds default ligatures so that pairs of
regional indicator characters for which there's no predefined glyph
get a 'missing flag' glyph.  This avoids cases where sequences of
regional indicator sequences accidentally match at odd locations
because of a previous mismatch.

There is no actual 'missing flag' glyph yet.  The code uses an
existing emoji as a placeholder.

Makefile

@@ -44,7 +44,7 @@ QUANTIZED_DIR := $(BUILD_DIR)/quantized_pngs
 COMPRESSED_DIR := $(BUILD_DIR)/compressed_pngs
 
 LIMITED_FLAGS = CN DE ES FR GB IT JP KR RU US
-SELECTED_FLAGS = AD AE AF AG AI AL AM AO AR AS AT AU AW AX AZ \
+SELECTED_FLAGS = AC AD AE AF AG AI AL AM AO AQ AR AS AT AU AW AX AZ \
 	BA BB BD BE BF BG BH BI BJ BM BN BO BR BS BT BW BY BZ \
 	CA CC CD CF CG CH CI CK CL CM CN CO CR CU CV CW CX CY CZ \
 	DE DJ DK DM DO DZ \
@@ -52,7 +52,7 @@ SELECTED_FLAGS = AD AE AF AG AI AL AM AO AR AS AT AU AW AX AZ \
 	FI FJ FM FO FR \
 	GA GB GD GE GG GH GI GL GM GN GQ GR GT GU GW GY \
 	HK HN HR HT HU \
-	ID IE IL IM IN IO IQ IR IS IT \
+	IC ID IE IL IM IN IO IQ IR IS IT \
 	JE JM JO JP \
 	KE KG KH KI KM KN KP KR KW KY KZ \
 	LA LB LC LI LK LR LS LT LU LV LY \
@@ -62,8 +62,8 @@ SELECTED_FLAGS = AD AE AF AG AI AL AM AO AR AS AT AU AW AX AZ \
 	PA PE PF PG PH PK PL PN PR PS PT PW PY \
 	QA \
 	RO RS RU RW \
-	SA SB SC SD SE SG SI SK SL SM SN SO SR SS ST SV SX SY SZ \
+	SA SB SC SD SE SG SH SI SK SL SM SN SO SR SS ST SV SX SY SZ \
-	TC TD TG TH TJ TK TL TM TN TO TR TT TV TW TZ \
+	TA TC TD TG TH TJ TK TL TM TN TO TR TT TV TW TZ \
 	UA UG US UY UZ \
 	VA VC VE VG VI VN VU \
 	WS \

third_party/color_emoji/add_glyphs.py

@@ -1,10 +1,13 @@
 #!/usr/bin/env python
 
-import collections, glob, os, sys
+import collections, glob, os, re, sys
 from fontTools import ttx
 from fontTools.ttLib.tables import otTables
 from png import PNG
 
+# TODO: replace with actual name once we have a glyph.
+MISSING_FLAG_GLYPH_NAME = "u2764"
+
 sys.path.append(
     os.path.join(os.path.dirname(__file__), os.pardir, os.pardir))
 import add_emoji_gsub
@@ -78,6 +81,15 @@ EXTRA_SEQUENCES = {
     'u1F48F': '1F469_200D_2764_FE0F_200D_1F48B_200D_1F468', # WHKM
 }
 
+# Flag aliases - from: to
+FLAG_ALIASES = {
+    'BV': 'NO',
+    'SJ': 'NO',
+    'UM': 'FR',
+    'HM': 'AU',
+    'UM': 'US',
+}
+
 if len (sys.argv) < 4:
 	print >>sys.stderr, """
 Usage:
@@ -180,6 +192,49 @@ for n in EXTRA_SEQUENCES:
         else:
                 print 'extras: no glyph for %s' % n
 
+# Add missing regional indicator sequences and flag aliases
+# if we support any.
+regional_names = frozenset('u%X' % cp for cp in range(0x1F1E6, 0x1F200))
+
+def _is_flag_sequence(t):
+  return len(t) == 2 and t[0] in regional_names and t[1] in regional_names
+
+have_flags = False
+for k in ligatures:
+  if _is_flag_sequence(k):
+    have_flags = True
+    break
+
+# sigh, too many separate files with the same code.
+# copied from add_emoji_gsub.
+def _reg_indicator(letter):
+  assert 'A' <= letter <= 'Z'
+  return 0x1F1E6 + ord(letter) - ord('A')
+
+def _reg_lig_sequence(flag_name):
+  """Returns a tuple of strings naming the codepoints that form the ligature."""
+  assert len(flag_name) == 2
+  return tuple('u%X' % _reg_indicator(cp) for cp in flag_name)
+
+def _reg_lig_name(flag_name):
+  """Returns a glyph name for the flag name."""
+  return '_'.join(_reg_lig_sequence(flag_name))
+
+if have_flags:
+  print 'Adding flag aliases.'
+  for flag_from, flag_to in FLAG_ALIASES.iteritems():
+    seq = _reg_lig_sequence(flag_from)
+    name = _reg_lig_name(flag_to)
+    add_lig_sequence(ligatures, seq, name)
+
+  print 'Adding unused flag sequences'
+  # every flag sequence we don't have gets the missing flag glyph
+  for first in regional_names:
+    for second in regional_names:
+      seq = (first, second)
+      if seq not in ligatures:
+        add_lig_sequence(ligatures, seq, MISSING_FLAG_GLYPH_NAME)
+
 
 keyed_ligatures = collections.defaultdict(list)
 for k, v in ligatures.iteritems():