[varLib.mutator] Add interpolation of glyph metrics.

Added interpolation of glyph advance width, from HVAR/hmtx, and derivation of new LSB.
Updated tests to match.
Needed to cherrypick from another branch an update for psCharstrings to allow the CFFSubr.draw() method to work.

Lib/fontTools/subset/cffLib.py

@@ -1,7 +1,9 @@
 from fontTools.misc import psCharStrings
 from fontTools import ttLib
 from fontTools.pens.basePen import NullPen
+from fontTools.pens.boundsPen import BoundsPen
 from fontTools.misc.fixedTools import otRound
+from fontTools.varLib.varStore import VarStoreInstancer
 
 def _add_method(*clazzes):
 	"""Returns a decorator function that adds a new method to one or
@@ -587,6 +589,7 @@ def interpolate_cff2_PrivateDict(topDict, interpolateFromDeltas):
 def interpolate_cff2_charstrings(topDict, interpolateFromDeltas, glyphOrder):
 	charstrings = topDict.CharStrings
 	for gname in glyphOrder:
+		# Interpolate charstring
 		charstring = charstrings[gname]
 		pd = charstring.private
 		vsindex = pd.vsindex if (hasattr(pd, 'vsindex')) else 0
@@ -620,4 +623,50 @@ def interpolate_cff2_charstrings(topDict, interpolateFromDeltas, glyphOrder):
 			charstring.program = new_program
 
 
+def interpolate_cff2_metrics(varfont, topDict, glyphOrder, loc):
+	"""Unlike TrueType glyphs, neither advance width nor bounding box
+	info is stored in a CFF2 charstring. The width data exists only in
+	the hmtx and HVAR tables. Since LSB data cannot be interpolated
+	reliably from the master LSB values in the hmtx table, we traverse
+	the charstring to determine the actual bound box. """
+
+	charstrings = topDict.CharStrings
+	boundsPen = BoundsPen(glyphOrder)
+	hmtx = varfont['hmtx']
+	hvar_table = None
+	if 'HVAR' in varfont:
+		hvar_table = varfont['HVAR'].table
+		fvar = varfont['fvar']
+		varStoreInstancer = VarStoreInstancer(hvar_table.VarStore, fvar.axes, loc)
+
+	for gid, gname in enumerate(glyphOrder):
+		entry = list(hmtx[gname])
+		# get width delta.
+		if hvar_table:
+			if hvar_table.AdvWidthMap:
+				width_idx = hvar_table.AdvWidthMap.mapping[gname]
+			else:
+				width_idx = gid
+			width_delta = otRound(varStoreInstancer[width_idx])
+		else:
+			width_delta = 0
+
+		# get LSB.
+		boundsPen.init()
+		charstring = charstrings[gname]
+		charstring.draw(boundsPen)
+		if boundsPen.bounds is None:
+			# Happens with non-marking glyphs
+			lsb_delta = 0
+		else:
+			lsb = boundsPen.bounds[0]
+		lsb_delta = entry[1] - lsb
+
+		if lsb_delta or width_delta:
+			if width_delta:
+				entry[0] += width_delta
+			if lsb_delta:
+				entry[1] = lsb
+			hmtx[gname] = tuple(entry)
+
 

Lib/fontTools/varLib/mutator.py

@@ -17,7 +17,9 @@ from fontTools.varLib.merger import MutatorMerger
 from fontTools.varLib.varStore import VarStoreInstancer
 from fontTools.varLib.mvar import MVAR_ENTRIES
 from fontTools.varLib.iup import iup_delta
-from  fontTools.subset.cffLib import interpolate_cff2_PrivateDict, interpolate_cff2_charstrings
+from  fontTools.subset.cffLib import (interpolate_cff2_PrivateDict,
+										interpolate_cff2_charstrings,
+										interpolate_cff2_metrics)
 import os.path
 import logging
 
@@ -106,7 +108,7 @@ def instantiateVariableFont(varfont, location, inplace=False):
 	if 'CFF2' in varfont:
 		log.info("Mutating CFF2 table")
 		glyphOrder = varfont.getGlyphOrder()
-		CFF2= varfont['CFF2']
+		CFF2 = varfont['CFF2']
 		topDict = CFF2.cff.topDictIndex[0]
 		vsInstancer = VarStoreInstancer(topDict.VarStore.otVarStore,
 										fvar.axes, loc)
@@ -115,6 +117,9 @@ def instantiateVariableFont(varfont, location, inplace=False):
 		CFF2.desubroutinize(varfont)
 		interpolate_cff2_charstrings(topDict, interpolateFromDeltas,
 										glyphOrder)
+		interpolate_cff2_metrics(varfont, topDict, glyphOrder, loc)
+		del topDict.rawDict['VarStore']
+		del topDict.VarStore
 
 	if 'MVAR' in varfont:
 		log.info("Mutating MVAR table")

Tests/varLib/data/test_results/InterpolateTestCFF2VF.ttx

@@ -1,6 +1,14 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <ttFont sfntVersion="OTTO" ttLibVersion="3.32">
 
+  <hmtx>
+    <mtx name=".notdef" width="600" lsb="84"/>
+    <mtx name="A" width="600" lsb="50"/>
+    <mtx name="T" width="600" lsb="50"/>
+    <mtx name="dollar" width="600" lsb="102"/>
+    <mtx name="glyph00003" width="600" lsb="102"/>
+  </hmtx>
+
   <CFF2>
     <major value="2"/>
     <minor value="0"/>
@@ -89,35 +97,6 @@
           158 860 -30 4 -158 -860 rlineto
         </CharString>
       </CharStrings>
-      <VarStore Format="1">
-        <Format value="1"/>
-        <VarRegionList>
-          <!-- RegionAxisCount=1 -->
-          <!-- RegionCount=2 -->
-          <Region index="0">
-            <VarRegionAxis index="0">
-              <StartCoord value="-1.0"/>
-              <PeakCoord value="-1.0"/>
-              <EndCoord value="0.0"/>
-            </VarRegionAxis>
-          </Region>
-          <Region index="1">
-            <VarRegionAxis index="0">
-              <StartCoord value="0.0"/>
-              <PeakCoord value="1.0"/>
-              <EndCoord value="1.0"/>
-            </VarRegionAxis>
-          </Region>
-        </VarRegionList>
-        <!-- VarDataCount=1 -->
-        <VarData index="0">
-          <!-- ItemCount=0 -->
-          <NumShorts value="0"/>
-          <!-- VarRegionCount=2 -->
-          <VarRegionIndex index="0" value="0"/>
-          <VarRegionIndex index="1" value="1"/>
-        </VarData>
-      </VarStore>
     </CFFFont>
 
     <GlobalSubrs>

Tests/varLib/mutator_test.py

@@ -165,7 +165,7 @@ class MutatorTest(unittest.TestCase):
 
         otf_vf_path = self.get_test_input('TestCFF2VF.otf')
         expected_ttx_name = 'InterpolateTestCFF2VF'
-        tables = ["fvar", "CFF2"]
+        tables = ["hmtx", "CFF2"]
         loc = {'wght':float(200)}
 
         varfont = TTFont(otf_vf_path)