[misc.roundTools] Add noRound(), maybeRound(), and roundFunc()

Moving out of CFF code, to be used in VariationModel().

Part of https://github.com/fonttools/fonttools/issues/2213

Lib/fontTools/misc/roundTools.py

@@ -3,14 +3,21 @@ Various round-to-integer helpers.
 """
 
 import math
+import functools
 import logging
 
 log = logging.getLogger(__name__)
 
 __all__ = [
+	"noRound",
 	"otRound",
+	"maybeRound",
+	"roundFunc",
 ]
 
+def noRound(value):
+	return value
+
 def otRound(value):
 	"""Round float value to nearest integer towards ``+Infinity``.
 
@@ -34,3 +41,18 @@ def otRound(value):
 	# https://github.com/fonttools/fonttools/issues/1248#issuecomment-383198166
 	return int(math.floor(value + 0.5))
 
+def maybeRound(v, tolerance, round=otRound):
+	rounded = round(v)
+	return rounded if abs(rounded - v) <= tolerance else v
+
+def roundFunc(tolerance, round=otRound):
+    if tolerance < 0:
+        raise ValueError("Rounding tolerance must be positive")
+
+    if tolerance == 0:
+        return noRound
+
+    if tolerance >= .5:
+        return round
+
+    return functools.partial(maybeRound, tolerance=tolerance, round=round)

Lib/fontTools/pens/t2CharStringPen.py

@@ -1,29 +1,12 @@
 # Copyright (c) 2009 Type Supply LLC
 # Author: Tal Leming
 
-from fontTools.misc.roundTools import otRound
+from fontTools.misc.roundTools import otRound, roundFunc
 from fontTools.misc.psCharStrings import T2CharString
 from fontTools.pens.basePen import BasePen
 from fontTools.cffLib.specializer import specializeCommands, commandsToProgram
 
 
-def roundFunc(tolerance, round=otRound):
-    if tolerance < 0:
-        raise ValueError("Rounding tolerance must be positive")
-
-    if tolerance == 0:
-        return lambda x: x
-
-    if tolerance >= .5:
-        return round
-
-    def maybe_round(v):
-        rounded = round(v)
-        return rounded if abs(rounded - v) <= tolerance else v
-
-    return maybe_round
-
-
 class T2CharStringPen(BasePen):
     """Pen to draw Type 2 CharStrings.
 

Lib/fontTools/varLib/cff.py

@@ -17,8 +17,9 @@ from fontTools.cffLib.specializer import (
 from fontTools.ttLib import newTable
 from fontTools import varLib
 from fontTools.varLib.models import allEqual
+from fontTools.misc.roundTools import roundFunc
 from fontTools.misc.psCharStrings import T2CharString, T2OutlineExtractor
-from fontTools.pens.t2CharStringPen import T2CharStringPen, roundFunc
+from fontTools.pens.t2CharStringPen import T2CharStringPen
 
 from .errors import VarLibCFFDictMergeError, VarLibCFFPointTypeMergeError, VarLibMergeError