[varLib] Shift most (all?) delta-rounding to VarModel

Reduces error.

The main varfont-builder now asks the model to do rounding, and asks
VariationStore to do no rounding, so we don't spend extra times rounding
multiple times (specially with the heavy otRound).

I *think* I got it all and right...

Fixes https://github.com/fonttools/fonttools/issues/2213

Lib/fontTools/varLib/__init__.py

@@ -19,7 +19,7 @@ Then you can make a variable-font this way:
 API *will* change in near future.
 """
 from fontTools.misc.py23 import *
-from fontTools.misc.fixedTools import otRound
+from fontTools.misc.roundTools import noRound, otRound
 from fontTools.misc.vector import Vector
 from fontTools.ttLib import TTFont, newTable
 from fontTools.ttLib.tables._f_v_a_r import Axis, NamedInstance
@@ -253,7 +253,7 @@ def _add_gvar(font, masterModel, master_ttfs, tolerance=0.5, optimize=True):
 
 		# Update gvar
 		gvar.variations[glyph] = []
-		deltas = model.getDeltas(allCoords)
+		deltas = model.getDeltas(allCoords, round=round) # builtin round calls into GlyphCoordinates.__round__()
 		supports = model.supports
 		assert len(deltas) == len(supports)
 
@@ -262,7 +262,7 @@ def _add_gvar(font, masterModel, master_ttfs, tolerance=0.5, optimize=True):
 		endPts = control.endPts
 
 		for i,(delta,support) in enumerate(zip(deltas[1:], supports[1:])):
-			if all(abs(v) <= tolerance for v in delta.array) and not isComposite:
+			if all(v == 0 for v in delta.array) and not isComposite:
 				continue
 			var = TupleVariation(support, delta)
 			if optimize:
@@ -304,7 +304,7 @@ def _remove_TTHinting(font):
 	font["glyf"].removeHinting()
 	# TODO: Modify gasp table to deactivate gridfitting for all ranges?
 
-def _merge_TTHinting(font, masterModel, master_ttfs, tolerance=0.5):
+def _merge_TTHinting(font, masterModel, master_ttfs):
 
 	log.info("Merging TT hinting")
 	assert "cvar" not in font
@@ -363,10 +363,9 @@ def _merge_TTHinting(font, masterModel, master_ttfs, tolerance=0.5):
 		return
 
 	variations = []
-	deltas, supports = masterModel.getDeltasAndSupports(all_cvs)
+	deltas, supports = masterModel.getDeltasAndSupports(all_cvs, round=round) # builtin round calls into Vector.__round__
 	for i,(delta,support) in enumerate(zip(deltas[1:], supports[1:])):
-		delta = [otRound(d) for d in delta]
+		if all(v == 0 for v in delta):
-		if all(abs(v) <= tolerance for v in delta):
 			continue
 		var = TupleVariation(support, delta)
 		variations.append(var)
@@ -441,7 +440,7 @@ def _get_advance_metrics(font, masterModel, master_ttfs,
 	vOrigDeltasAndSupports = {}
 	for glyph in glyphOrder:
 		vhAdvances = [metrics[glyph][0] if glyph in metrics else None for metrics in advMetricses]
-		vhAdvanceDeltasAndSupports[glyph] = masterModel.getDeltasAndSupports(vhAdvances)
+		vhAdvanceDeltasAndSupports[glyph] = masterModel.getDeltasAndSupports(vhAdvances, round=otRound)
 
 	singleModel = models.allEqual(id(v[1]) for v in vhAdvanceDeltasAndSupports.values())
 
@@ -453,7 +452,7 @@ def _get_advance_metrics(font, masterModel, master_ttfs,
 			# glyphs which have a non-default vOrig.
 			vOrigs = [metrics[glyph] if glyph in metrics else defaultVOrig
 				for metrics, defaultVOrig in vOrigMetricses]
-			vOrigDeltasAndSupports[glyph] = masterModel.getDeltasAndSupports(vOrigs)
+			vOrigDeltasAndSupports[glyph] = masterModel.getDeltasAndSupports(vOrigs, round=otRound)
 
 	directStore = None
 	if singleModel:
@@ -463,7 +462,7 @@ def _get_advance_metrics(font, masterModel, master_ttfs,
 		varTupleIndexes = list(range(len(supports)))
 		varData = builder.buildVarData(varTupleIndexes, [], optimize=False)
 		for glyphName in glyphOrder:
-			varData.addItem(vhAdvanceDeltasAndSupports[glyphName][0])
+			varData.addItem(vhAdvanceDeltasAndSupports[glyphName][0], round=noRound)
 		varData.optimize()
 		directStore = builder.buildVarStore(varTupleList, [varData])
 
@@ -473,14 +472,14 @@ def _get_advance_metrics(font, masterModel, master_ttfs,
 	for glyphName in glyphOrder:
 		deltas, supports = vhAdvanceDeltasAndSupports[glyphName]
 		storeBuilder.setSupports(supports)
-		advMapping[glyphName] = storeBuilder.storeDeltas(deltas)
+		advMapping[glyphName] = storeBuilder.storeDeltas(deltas, round=noRound)
 
 	if vOrigMetricses:
 		vOrigMap = {}
 		for glyphName in glyphOrder:
 			deltas, supports = vOrigDeltasAndSupports[glyphName]
 			storeBuilder.setSupports(supports)
-			vOrigMap[glyphName] = storeBuilder.storeDeltas(deltas)
+			vOrigMap[glyphName] = storeBuilder.storeDeltas(deltas, round=noRound)
 
 	indirectStore = storeBuilder.finish()
 	mapping2 = indirectStore.optimize()

Lib/fontTools/varLib/cff.py

@@ -20,6 +20,7 @@ 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
+from functools import partial
 
 from .errors import VarLibCFFDictMergeError, VarLibCFFPointTypeMergeError, VarLibMergeError
 
@@ -585,7 +586,7 @@ class CFF2CharStringMergePen(T2CharStringPen):
 	def getCommands(self):
 		return self._commands
 
-	def reorder_blend_args(self, commands, get_delta_func, round_func):
+	def reorder_blend_args(self, commands, get_delta_func):
 		"""
 		We first re-order the master coordinate values.
 		For a moveto to lineto, the args are now arranged as:
@@ -628,8 +629,6 @@ class CFF2CharStringMergePen(T2CharStringPen):
 					else:
 						# convert to deltas
 						deltas = get_delta_func(coord)[1:]
-						if round_func:
-							deltas = [round_func(delta) for delta in deltas]
 						coord = [coord[0]] + deltas
 						new_coords.append(coord)
 				cmd[1] = new_coords
@@ -640,7 +639,7 @@ class CFF2CharStringMergePen(T2CharStringPen):
 					self, private=None, globalSubrs=None,
 					var_model=None, optimize=True):
 		commands = self._commands
-		commands = self.reorder_blend_args(commands, var_model.getDeltas, self.round)
+		commands = self.reorder_blend_args(commands, partial (var_model.getDeltas, round=self.round))
 		if optimize:
 			commands = specializeCommands(
 						commands, generalizeFirst=False,

Lib/fontTools/varLib/varStore.py

@@ -1,4 +1,4 @@
-from fontTools.misc.fixedTools import otRound
+from fontTools.misc.roundTools import noRound, otRound
 from fontTools.ttLib.tables import otTables as ot
 from fontTools.varLib.models import supportScalar
 from fontTools.varLib.builder import (buildVarRegionList, buildVarStore,
@@ -83,15 +83,12 @@ class OnlineVarStoreBuilder(object):
 
 
 	def storeMasters(self, master_values):
-		deltas = self._model.getDeltas(master_values)
+		deltas = self._model.getDeltas(master_values, round=otRound)
-		base = otRound(deltas.pop(0))
+		base = deltas.pop(0)
-		return base, self.storeDeltas(deltas)
+		return base, self.storeDeltas(deltas, round=noRound)
 
-	def storeDeltas(self, deltas):
+	def storeDeltas(self, deltas, round=otRound):
-		# Pity that this exists here, since VarData_addItem
+		deltas = [round(d) for d in deltas]
-		# does the same.  But to look into our cache, it's
-		# good to adjust deltas here as well...
-		deltas = [otRound(d) for d in deltas]
 		if len(deltas) == len(self._supports) + 1:
 			deltas = tuple(deltas[1:])
 		else:
@@ -109,14 +106,14 @@ class OnlineVarStoreBuilder(object):
 			# Full array. Start new one.
 			self._add_VarData()
 			return self.storeDeltas(deltas)
-		self._data.addItem(deltas)
+		self._data.addItem(deltas, round=noRound)
 
 		varIdx = (self._outer << 16) + inner
 		self._cache[deltas] = varIdx
 		return varIdx
 
-def VarData_addItem(self, deltas):
+def VarData_addItem(self, deltas, round=otRound):
-	deltas = [otRound(d) for d in deltas]
+	deltas = [round(d) for d in deltas]
 
 	countUs = self.VarRegionCount
 	countThem = len(deltas)

Tests/varLib/data/test_results/TestSparseCFF2VF.ttx

@@ -290,7 +290,7 @@
         </CharString>
         <CharString name="cid06449" fdSelectIndex="1">
           2 vsindex
-          -60 30 203 30 -9 9 67 7 -7 14 -14 30 -20 20 80 30 59 30 121 30 18 93 -30 30 -30 108 -23 0 -26 67 2 76 -98 -2 -111 42 0 47 -13 0 -14 13 0 14 -33 0 -37 11 0 13 -11 0 -13 8 0 9 -7 0 -8 53 0 60 -32 0 -36 32 0 36 -52 0 -59 57 1 65 -33 0 -38 53 0 60 -83 -1 -93 54 0 60 -6 -19 -24 33 19 55 -76 -1 -86 76 1 86 -76 -1 -86 59 1 67 26 blend
+          -60 30 203 30 -9 9 67 7 -7 14 -14 30 -20 20 80 30 59 30 121 30 18 93 -30 30 -30 108 -23 0 -26 67 2 76 -98 -2 -111 42 0 47 -13 0 -14 13 0 14 -33 0 -37 11 0 13 -11 0 -13 8 0 9 -7 -1 -8 53 0 60 -32 0 -36 32 0 36 -52 0 -59 57 1 65 -33 0 -38 53 0 60 -83 -1 -93 54 0 60 -6 -19 -24 33 19 55 -76 -1 -86 76 1 86 -76 -1 -86 59 1 67 26 blend
           hstemhm
           77 30 42 30 139 30 23 30 71 10 74 30 15 30 16 30 158 30 28 30 -4 29 -14 0 -16 88 1 99 -82 -1 -92 87 1 98 -130 -1 -146 102 1 114 -73 -1 -82 74 2 84 -112 -2 -126 27 0 30 13 0 15 90 1 101 -126 -1 -142 75 1 84 -68 -1 -76 102 1 115 -144 -1 -162 94 1 105 -79 -1 -88 95 1 106 -81 -1 -91 74 1 83 22 blend
           vstemhm