[config] Add new config module and use it for GPOS compression level

Lib/fontTools/config/__init__.py

@@ -0,0 +1,41 @@
+"""
+Define all configuration options that can affect the working of fontTools
+modules. E.g. optimization levels of varLib IUP, otlLib GPOS compression level,
+etc. If this file gets too big, split it into smaller files per-module.
+
+An instance of the Config class can be attached to a TTFont object, so that
+the various modules can access their configuration options from it.
+"""
+from textwrap import dedent
+
+from fontTools.misc.configTools import *
+
+
+class Config(AbstractConfig):
+    options = Options()
+
+OPTIONS = Config.options
+
+Config.register_option(
+    name="fontTools.otlLib.optimize.gpos:COMPRESSION_LEVEL",
+    help=dedent(
+        """\
+        GPOS Lookup type 2 (PairPos) compression level:
+            0 = do not attempt to compact PairPos lookups;
+            1 to 8 = create at most 1 to 8 new subtables for each existing
+                subtable, provided that it would yield a 50%% file size saving;
+            9 = create as many new subtables as needed to yield a file size saving.
+        Default: 0.
+
+        This compaction aims to save file size, by splitting large class
+        kerning subtables (Format 2) that contain many zero values into
+        smaller and denser subtables. It's a trade-off between the overhead
+        of several subtables versus the sparseness of one big subtable.
+
+        See the pull request: https://github.com/fonttools/fonttools/pull/2326
+        """
+    ),
+    default=0,
+    parse=int,
+    validate=lambda v: v in range(10),
+)

Lib/fontTools/otlLib/builder.py

@@ -11,11 +11,7 @@ from fontTools.ttLib.tables.otBase import (
 )
 from fontTools.ttLib.tables import otBase
 from fontTools.feaLib.ast import STATNameStatement
-from fontTools.otlLib.optimize.gpos import (
-    GPOS_COMPACT_MODE_DEFAULT,
-    GPOS_COMPACT_MODE_ENV_KEY,
-    compact_lookup,
-)
+from fontTools.otlLib.optimize.gpos import compact_lookup
 from fontTools.otlLib.error import OpenTypeLibError
 from functools import reduce
 import logging
@@ -1414,10 +1410,10 @@ class PairPosBuilder(LookupBuilder):
         # Compact the lookup
         # This is a good moment to do it because the compaction should create
         # smaller subtables, which may prevent overflows from happening.
-        mode = os.environ.get(GPOS_COMPACT_MODE_ENV_KEY, GPOS_COMPACT_MODE_DEFAULT)
-        if mode and mode != "0":
+        level = self.font.cfg["fontTools.otlLib.optimize.gpos:COMPRESSION_LEVEL"]
+        if level and level != 0:
             log.info("Compacting GPOS...")
-            compact_lookup(self.font, mode, lookup)
+            compact_lookup(self.font, level, lookup)
 
         return lookup
 

Lib/fontTools/otlLib/optimize/__init__.py

@@ -1,39 +1,30 @@
 from argparse import RawTextHelpFormatter
-from textwrap import dedent
+from fontTools.config import OPTIONS
 
+from fontTools.otlLib.optimize.gpos import compact
 from fontTools.ttLib import TTFont
-from fontTools.otlLib.optimize.gpos import compact, GPOS_COMPACT_MODE_DEFAULT
+
 
 def main(args=None):
     """Optimize the layout tables of an existing font."""
     from argparse import ArgumentParser
+
     from fontTools import configLogger
 
-    parser = ArgumentParser(prog="otlLib.optimize", description=main.__doc__, formatter_class=RawTextHelpFormatter)
+    parser = ArgumentParser(
+        prog="otlLib.optimize",
+        description=main.__doc__,
+        formatter_class=RawTextHelpFormatter,
+    )
     parser.add_argument("font")
     parser.add_argument(
         "-o", metavar="OUTPUTFILE", dest="outfile", default=None, help="output file"
     )
+    COMPRESSION_LEVEL = OPTIONS["fontTools.otlLib.optimize.gpos:COMPRESSION_LEVEL"]
     parser.add_argument(
-        "--gpos-compact-mode",
-        help=dedent(
-            f"""\
-            GPOS Lookup type 2 (PairPos) compaction mode:
-                0 = do not attempt to compact PairPos lookups;
-                1 to 8 = create at most 1 to 8 new subtables for each existing
-                    subtable, provided that it would yield a 50%% file size saving;
-                9 = create as many new subtables as needed to yield a file size saving.
-            Default: {GPOS_COMPACT_MODE_DEFAULT}.
-
-            This compaction aims to save file size, by splitting large class
-            kerning subtables (Format 2) that contain many zero values into
-            smaller and denser subtables. It's a trade-off between the overhead
-            of several subtables versus the sparseness of one big subtable.
-
-            See the pull request: https://github.com/fonttools/fonttools/pull/2326
-            """
-        ),
-        default=int(GPOS_COMPACT_MODE_DEFAULT),
+        "--gpos-compression-level",
+        help=COMPRESSION_LEVEL.help,
+        default=COMPRESSION_LEVEL.default,
         choices=list(range(10)),
         type=int,
     )
@@ -51,12 +42,10 @@ def main(args=None):
     )
 
     font = TTFont(options.font)
-    # TODO: switch everything to have type(mode) = int when using the Config class
-    compact(font, str(options.gpos_compact_mode))
+    compact(font, options.gpos_compression_level)
     font.save(options.outfile or options.font)
 
 
-
 if __name__ == "__main__":
     import sys
 
@@ -65,4 +54,3 @@ if __name__ == "__main__":
     import doctest
 
     sys.exit(doctest.testmod().failed)
-

Lib/fontTools/otlLib/optimize/gpos.py

@@ -9,16 +9,10 @@ from fontTools.misc.intTools import bit_count, bit_indices
 from fontTools.ttLib import TTFont
 from fontTools.ttLib.tables import otBase, otTables
 
-# NOTE: activating this optimization via the environment variable is
-# experimental and may not be supported once an alternative mechanism
-# is in place. See: https://github.com/fonttools/fonttools/issues/2349
-GPOS_COMPACT_MODE_ENV_KEY = "FONTTOOLS_GPOS_COMPACT_MODE"
-GPOS_COMPACT_MODE_DEFAULT = "0"
-
 log = logging.getLogger("fontTools.otlLib.optimize.gpos")
 
 
-def compact(font: TTFont, mode: str) -> TTFont:
+def compact(font: TTFont, level: int) -> TTFont:
     # Ideal plan:
     #  1. Find lookups of Lookup Type 2: Pair Adjustment Positioning Subtable
     #     https://docs.microsoft.com/en-us/typography/opentype/spec/gpos#lookup-type-2-pair-adjustment-positioning-subtable
@@ -35,21 +29,21 @@ def compact(font: TTFont, mode: str) -> TTFont:
     gpos = font["GPOS"]
     for lookup in gpos.table.LookupList.Lookup:
         if lookup.LookupType == 2:
-            compact_lookup(font, mode, lookup)
+            compact_lookup(font, level, lookup)
         elif lookup.LookupType == 9 and lookup.SubTable[0].ExtensionLookupType == 2:
-            compact_ext_lookup(font, mode, lookup)
+            compact_ext_lookup(font, level, lookup)
     return font
 
 
-def compact_lookup(font: TTFont, mode: str, lookup: otTables.Lookup) -> None:
-    new_subtables = compact_pair_pos(font, mode, lookup.SubTable)
+def compact_lookup(font: TTFont, level: int, lookup: otTables.Lookup) -> None:
+    new_subtables = compact_pair_pos(font, level, lookup.SubTable)
     lookup.SubTable = new_subtables
     lookup.SubTableCount = len(new_subtables)
 
 
-def compact_ext_lookup(font: TTFont, mode: str, lookup: otTables.Lookup) -> None:
+def compact_ext_lookup(font: TTFont, level: int, lookup: otTables.Lookup) -> None:
     new_subtables = compact_pair_pos(
-        font, mode, [ext_subtable.ExtSubTable for ext_subtable in lookup.SubTable]
+        font, level, [ext_subtable.ExtSubTable for ext_subtable in lookup.SubTable]
     )
     new_ext_subtables = []
     for subtable in new_subtables:
@@ -62,7 +56,7 @@ def compact_ext_lookup(font: TTFont, mode: str, lookup: otTables.Lookup) -> None
 
 
 def compact_pair_pos(
-    font: TTFont, mode: str, subtables: Sequence[otTables.PairPos]
+    font: TTFont, level: int, subtables: Sequence[otTables.PairPos]
 ) -> Sequence[otTables.PairPos]:
     new_subtables = []
     for subtable in subtables:
@@ -70,12 +64,12 @@ def compact_pair_pos(
             # Not doing anything to Format 1 (yet?)
             new_subtables.append(subtable)
         elif subtable.Format == 2:
-            new_subtables.extend(compact_class_pairs(font, mode, subtable))
+            new_subtables.extend(compact_class_pairs(font, level, subtable))
     return new_subtables
 
 
 def compact_class_pairs(
-    font: TTFont, mode: str, subtable: otTables.PairPos
+    font: TTFont, level: int, subtable: otTables.PairPos
 ) -> List[otTables.PairPos]:
     from fontTools.otlLib.builder import buildPairPosClassesSubtable
 
@@ -95,17 +89,9 @@ def compact_class_pairs(
                 getattr(class2, "Value1", None),
                 getattr(class2, "Value2", None),
             )
-
-    if len(mode) == 1 and mode in "123456789":
-        grouped_pairs = cluster_pairs_by_class2_coverage_custom_cost(
-            font, all_pairs, int(mode)
-        )
-        for pairs in grouped_pairs:
-            subtables.append(
-                buildPairPosClassesSubtable(pairs, font.getReverseGlyphMap())
-            )
-    else:
-        raise ValueError(f"Bad {GPOS_COMPACT_MODE_ENV_KEY}={mode}")
+    grouped_pairs = cluster_pairs_by_class2_coverage_custom_cost(font, all_pairs, level)
+    for pairs in grouped_pairs:
+        subtables.append(buildPairPosClassesSubtable(pairs, font.getReverseGlyphMap()))
     return subtables
 
 

Lib/fontTools/ttLib/ttFont.py

@@ -1,4 +1,6 @@
+from fontTools.config import Config
 from fontTools.misc import xmlWriter
+from fontTools.misc.configTools import AbstractConfig
 from fontTools.misc.textTools import Tag, byteord, tostr
 from fontTools.misc.loggingTools import deprecateArgument
 from fontTools.ttLib import TTLibError
@@ -89,7 +91,7 @@ class TTFont(object):
 			sfntVersion="\000\001\000\000", flavor=None, checkChecksums=0,
 			verbose=None, recalcBBoxes=True, allowVID=NotImplemented, ignoreDecompileErrors=False,
 			recalcTimestamp=True, fontNumber=-1, lazy=None, quiet=None,
-			_tableCache=None):
+			_tableCache=None, cfg={}):
 		for name in ("verbose", "quiet"):
 			val = locals().get(name)
 			if val is not None:
@@ -101,6 +103,7 @@ class TTFont(object):
 		self.recalcTimestamp = recalcTimestamp
 		self.tables = {}
 		self.reader = None
+		self.cfg = cfg.copy() if isinstance(cfg, AbstractConfig) else Config(cfg)
 		self.ignoreDecompileErrors = ignoreDecompileErrors
 
 		if not file:

Lib/fontTools/varLib/merger.py

@@ -15,11 +15,7 @@ from fontTools.varLib.models import nonNone, allNone, allEqual, allEqualTo
 from fontTools.varLib.varStore import VarStoreInstancer
 from functools import reduce
 from fontTools.otlLib.builder import buildSinglePos
-from fontTools.otlLib.optimize.gpos import (
-    compact_pair_pos,
-    GPOS_COMPACT_MODE_DEFAULT,
-    GPOS_COMPACT_MODE_ENV_KEY,
-)
+from fontTools.otlLib.optimize.gpos import compact_pair_pos
 
 log = logging.getLogger("fontTools.varLib.merger")
 
@@ -850,10 +846,10 @@ def merge(merger, self, lst):
 		# Compact the merged subtables
 		# This is a good moment to do it because the compaction should create
 		# smaller subtables, which may prevent overflows from happening.
-		mode = os.environ.get(GPOS_COMPACT_MODE_ENV_KEY, GPOS_COMPACT_MODE_DEFAULT)
-		if mode and mode != "0":
+		level = merger.font.cfg["fontTools.otlLib.optimize.gpos:COMPRESSION_LEVEL"]
+		if level and level != 0:
 			log.info("Compacting GPOS...")
-			self.SubTable = compact_pair_pos(merger.font, mode, self.SubTable)
+			self.SubTable = compact_pair_pos(merger.font, level, self.SubTable)
 			self.SubTableCount = len(self.SubTable)
 
 	elif isSinglePos and flattened: