[varLib.mutator] Interpolating CFF2 tables. Makes fixes per recommendations

varLib.py. restore import of 'fontTools.misc.py23 import *'
varStore.py. Rename 'applyScalar' to 'interpolateFromDeltasAndScalars', and refactor common code with __git__item to a static method.
mutator.py. Update to reflect function name change to interpolateFromDeltasAndScalars. Changed some logic from one line to several lines for readability, and i to avoid flake8 warnings about line too long.

Lib/fontTools/varLib/mutator.py

@@ -31,7 +31,7 @@ for i, (prev, curr) in enumerate(zip(percents[:-1], percents[1:]), start=1):
 	OS2_WIDTH_CLASS_VALUES[half] = i
 
 
-def interpolate_cff2_PrivateDict(topDict, applyScalars):
+def interpolate_cff2_PrivateDict(topDict, interpolateFromDeltas):
 	pd_blend_lists = ("BlueValues", "OtherBlues", "FamilyBlues",
 						"FamilyOtherBlues", "StemSnapH",
 						"StemSnapV")
@@ -42,8 +42,8 @@ def interpolate_cff2_PrivateDict(topDict, applyScalars):
 		vsindex = pd.vsindex if (hasattr(pd, 'vsindex')) else 0
 		for key, value in pd.rawDict.items():
 			if (key in pd_blend_values) and isinstance(value, list):
-					deltas = value[1:]
-					pd.rawDict[key] = otRound(value[0] + applyScalars(vsindex, deltas))
+					delta = interpolateFromDeltas(vsindex, value[1:])
+					pd.rawDict[key] = otRound(value[0] + delta)
 			elif (key in pd_blend_lists) and isinstance(value[0], list):
 				"""If any argument in a BlueValues list is a blend list,
 				then they all are. The first value of each list is an
@@ -52,11 +52,12 @@ def interpolate_cff2_PrivateDict(topDict, applyScalars):
 				deltas to date to each successive absolute value."""
 				delta = 0
 				for i, val_list in enumerate(value):
-					delta += otRound(applyScalars(vsindex, val_list[1:]))
+					delta += otRound(interpolateFromDeltas(vsindex, 
+										val_list[1:]))
 					value[i] = val_list[0] + delta
 
 
-def interpolate_cff2_charstrings(topDict, applyScalars, glyphOrder):
+def interpolate_cff2_charstrings(topDict, interpolateFromDeltas, glyphOrder):
 	charstrings = topDict.CharStrings
 	for gname in glyphOrder:
 		charstring = charstrings[gname]
@@ -83,8 +84,8 @@ def interpolate_cff2_charstrings(topDict, applyScalars, glyphOrder):
 				while argi < end_args:
 					next_ti = tuplei + num_regions
 					deltas = charstring.program[tuplei:next_ti]
-					delta = otRound(applyScalars(vsindex, deltas))
-					charstring.program[argi] += delta
+					delta = interpolateFromDeltas(vsindex, deltas)
+					charstring.program[argi] += otRound(delta)
 					tuplei = next_ti
 					argi += 1
 				new_program.extend(charstring.program[last_i:end_args])
@@ -169,9 +170,10 @@ def instantiateVariableFont(varfont, location, inplace=False):
 		topDict = varfont['CFF2'].cff.topDictIndex[0]
 		vsInstancer = VarStoreInstancer(topDict.VarStore.otVarStore,
 										fvar.axes, loc)
-		applyScalars = vsInstancer.applyScalars
-		interpolate_cff2_PrivateDict(topDict, applyScalars)
-		interpolate_cff2_charstrings(topDict, applyScalars, glyphOrder)
+		interpolateFromDeltas = vsInstancer.interpolateFromDeltas
+		interpolate_cff2_PrivateDict(topDict, interpolateFromDeltas)
+		interpolate_cff2_charstrings(topDict, interpolateFromDeltas,
+										glyphOrder)
 
 	if 'MVAR' in varfont:
 		log.info("Mutating MVAR table")

Lib/fontTools/varLib/varStore.py

@@ -162,27 +162,26 @@ class VarStoreInstancer(object):
 			self._scalars[regionIdx] = scalar
 		return scalar
 
-	def __getitem__(self, varidx):
-
-		major, minor = varidx >> 16, varidx & 0xFFFF
-
-		varData = self._varData
-		scalars = [self._getScalar(ri) for ri in varData[major].VarRegionIndex]
-
-		deltas = varData[major].Item[minor]
+	@staticmethod
+	def interpolateFromDeltasAndScalars(deltas, scalars):
 		delta = 0.
 		for d,s in zip(deltas, scalars):
+			if not s: continue
 			delta += d * s
 		return delta
 
-	def applyScalars(self, varDataIndex, deltas):
+	def __getitem__(self, varidx):
+		major, minor = varidx >> 16, varidx & 0xFFFF
+		varData = self._varData
+		scalars = [self._getScalar(ri) for ri in varData[major].VarRegionIndex]
+		deltas = varData[major].Item[minor]
+		return interpolateFromDeltasAndScalars(deltas, scalars)
+
+	def interpolateFromDeltas(self, varDataIndex, deltas):
 		varData = self._varData
 		scalars = [self._getScalar(ri) for ri in
 					varData[varDataIndex].VarRegionIndex]
-		delta = 0.
-		for d,s in zip(deltas, scalars):
-			delta += d * s
-		return delta
+		return interpolateFromDeltasAndScalars(deltas, scalars)
 
 
 #

Tests/varLib/varLib_test.py

@@ -1,5 +1,5 @@
 from __future__ import print_function, division, absolute_import
-
+from fontTools.misc.py23 import *
 from fontTools.ttLib import TTFont
 from fontTools.varLib import build
 from fontTools.varLib import main as varLib_main