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[varLib.mutator] Improve CharString rounding #3481

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[varLib.mutator] Improve CharString rounding #3481

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8caf16c
[varLib.mutator] Add failing test for CFF2 rounding errors
khaledhosny Apr 13, 2024
5a347b7
[varLib.mutator] Improve CharString rounding
khaledhosny Apr 13, 2024
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6 changes: 5 additions & 1 deletion Lib/fontTools/pens/t2CharStringPen.py
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Expand Up @@ -47,7 +47,7 @@ def _closePath(self):
def _endPath(self):
pass

def getCharString(self, private=None, globalSubrs=None, optimize=True):
def getProgram(self, optimize=True):
commands = self._commands
if optimize:
maxstack = 48 if not self._CFF2 else 513
Expand All @@ -62,6 +62,10 @@ def getCharString(self, private=None, globalSubrs=None, optimize=True):
program.insert(0, otRound(self._width))
if not self._CFF2:
program.append("endchar")
return program

def getCharString(self, private=None, globalSubrs=None, optimize=True):
program = self.getProgram(optimize=optimize)
charString = T2CharString(
program=program, private=private, globalSubrs=globalSubrs
)
Expand Down
10 changes: 9 additions & 1 deletion Lib/fontTools/varLib/mutator.py
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Expand Up @@ -69,6 +69,8 @@ def interpolate_cff2_PrivateDict(topDict, interpolateFromDeltas):


def interpolate_cff2_charstrings(topDict, interpolateFromDeltas, glyphOrder):
from fontTools.pens.t2CharStringPen import T2CharStringPen

charstrings = topDict.CharStrings
for gname in glyphOrder:
# Interpolate charstring
Expand Down Expand Up @@ -100,7 +102,7 @@ def interpolate_cff2_charstrings(topDict, interpolateFromDeltas, glyphOrder):
next_ti = tuplei + num_regions
deltas = charstring.program[tuplei:next_ti]
delta = interpolateFromDeltas(vsindex, deltas)
charstring.program[argi] += otRound(delta)
charstring.program[argi] += delta
tuplei = next_ti
argi += 1
new_program.extend(charstring.program[last_i:end_args])
Expand All @@ -109,6 +111,12 @@ def interpolate_cff2_charstrings(topDict, interpolateFromDeltas, glyphOrder):
new_program.extend(charstring.program[last_i:])
charstring.program = new_program

# Rebuild charstring program by passing it through T2CharStringPen which
# will have the side effect of rounding coordinates.
t2Pen = T2CharStringPen(width=None, glyphSet=None)
charstring.draw(t2Pen)
charstring.program = t2Pen.getProgram(optimize=True)


def interpolate_cff2_metrics(varfont, topDict, glyphOrder, loc):
"""Unlike TrueType glyphs, neither advance width nor bounding box
Expand Down
147 changes: 147 additions & 0 deletions Tests/varLib/data/TestCFF2VFRounding.ttx
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@@ -0,0 +1,147 @@
<?xml version="1.0" encoding="UTF-8"?>
<ttFont sfntVersion="OTTO" ttLibVersion="4.51">

<GlyphOrder>
<!-- The 'id' attribute is only for humans; it is ignored when parsed. -->
<GlyphID id="0" name=".notdef"/>
<GlyphID id="1" name="glyph00001"/>
</GlyphOrder>

<head>
<!-- Most of this table will be recalculated by the compiler -->
<tableVersion value="1.0"/>
<fontRevision value="5.0"/>
<checkSumAdjustment value="0xbcbbec73"/>
<magicNumber value="0x5f0f3cf5"/>
<flags value="00000000 00000000"/>
<unitsPerEm value="4000"/>
<created value="Tue Apr 9 18:59:32 2024"/>
<modified value="Tue Apr 9 18:59:32 2024"/>
<xMin value="-4000"/>
<yMin value="-4000"/>
<xMax value="4000"/>
<yMax value="4000"/>
<macStyle value="00000000 00000010"/>
<lowestRecPPEM value="6"/>
<fontDirectionHint value="2"/>
<indexToLocFormat value="0"/>
<glyphDataFormat value="0"/>
</head>

<maxp>
<tableVersion value="0x5000"/>
<numGlyphs value="2"/>
</maxp>

<hmtx>
<mtx name=".notdef" width="4000" lsb="0"/>
<mtx name="glyph00001" width="4000" lsb="-228"/>
</hmtx>

<CFF2>
<major value="2"/>
<minor value="0"/>
<CFFFont name="CFF2Font">
<FontMatrix value="0.00025 0 0 0.00025 0 0"/>
<FDArray>
<FontDict index="0">
<Private>
<BlueScale value="0.039625"/>
<BlueShift value="7"/>
<BlueFuzz value="1"/>
<LanguageGroup value="0"/>
<ExpansionFactor value="0.06"/>
</Private>
</FontDict>
</FDArray>
<CharStrings>
<CharString name=".notdef">
</CharString>
<CharString name="glyph00001">
-216 -4 1 blend
-12 rmoveto
64 240 12 92 120 188 12 1 blend
-12 64 hhcurveto
24 12 60 8 1 blend
16 12 -4 12 -12 hvcurveto
-200 16 -48 8 68 vvcurveto
52 44 80 -8 1 blend
80 144 vhcurveto
908 1580 -40 -36 2 blend
8 0 80 -1048 4 -20 20 -8 3 blend
-68 rlineto
-500 8 156 -476 640 -140 20 148 156 -100 5 blend
hhcurveto
928 380 976 668 560 -268 336 -544 -472 -352 -276 -408 -212 24 24 -8 -20 8 -36 20 -24 60 40 84 40 -40 13 blend
hvcurveto
-12 hlineto
-16 204 -12 208 -12 220 4 -60 4 -48 4 -20 6 blend
rrcurveto
20 4 1 blend
-8 8 -16 -16 1 blend
-16 -100 -48 1 blend
-4 -8 -76 -4 -4 2 blend
vhcurveto
-20 -4 1 blend
-4 -8 -8 -8 -16 -372 -640 -360 -640 -380 -636 4 -4 -4 192 336 -160 -260 -28 -68 9 blend
-232 -388 -4 1 blend
-48 -8 8 1 blend
-212 -20 rrcurveto
-16 -16 -40 -8 1 blend
-36 -12 4 -12 8 hvcurveto
2508 80 -8 8 2 blend
</CharString>
</CharStrings>
<VarStore Format="1">
<Format value="1"/>
<VarRegionList>
<!-- RegionAxisCount=1 -->
<!-- RegionCount=1 -->
<Region index="0">
<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=1 -->
<VarRegionIndex index="0" value="0"/>
</VarData>
</VarStore>
</CFFFont>

<GlobalSubrs>
<!-- The 'index' attribute is only for humans; it is ignored when parsed. -->
</GlobalSubrs>
</CFF2>

<avar>
<version major="1" minor="0"/>
<segment axis="wght">
<mapping from="-1.0" to="-1.0"/>
<mapping from="0.0" to="0.0"/>
<mapping from="0.3333" to="0.3"/>
<mapping from="0.6667" to="0.63336"/>
<mapping from="1.0" to="1.0"/>
</segment>
</avar>

<fvar>

<!-- Weight -->
<Axis>
<AxisTag>wght</AxisTag>
<Flags>0x0</Flags>
<MinValue>400.0</MinValue>
<DefaultValue>400.0</DefaultValue>
<MaxValue>700.0</MaxValue>
<AxisNameID>256</AxisNameID>
</Axis>
</fvar>

</ttFont>
21 changes: 11 additions & 10 deletions Tests/varLib/data/test_results/InterpolateTestCFF2VF.ttx
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Expand Up @@ -34,35 +34,33 @@
84 hmoveto
432 660 -432 hlineto
48 -628 rmoveto
102 176 64 106 rlineto
4 hlineto
62 -106 100 -176 rlineto
102 176 64 106 4 0 62 -106 100 -176 rlineto
-342 42 rmoveto
536 vlineto
154 -270 rlineto
22 26 rmoveto
-56 92 -94 168 rlineto
302 hlineto
-94 -168 -54 -92 rlineto
-56 92 -94 168 302 0 -94 -168 -54 -92 rlineto
22 -26 rmoveto
152 270 rlineto
-536 vlineto
endchar
</CharString>
<CharString name="A">
50 hmoveto
32 hlineto
140 396 28 80 24 68 24 82 rlinecurve
4 hlineto
24 -82 24 -68 28 -80 138 -396 rcurveline
34 hlineto
-236 660 rlineto
24 -82 24 -68 28 -80 rrcurveto
138 -396 34 0 -236 660 rlineto
-28 hlineto
-134 -424 rmoveto
293 28 -293 hlineto
endchar
</CharString>
<CharString name="T">
284 hmoveto
32 632 234 28 -500 -28 234 hlineto
endchar
</CharString>
<CharString name="dollar">
311 34 rmoveto
Expand All @@ -74,14 +72,16 @@
-99 -78 -54 -88 hvcurveto
-166 338 28 -156 vvcurveto
-70 -56 -50 -103 -85 -66 38 34 -40 vhcurveto
-18 -22 45 -38 73 -40 91 0 rlinecurve
-18 -22 rlineto
-38 45 73 -40 91 hhcurveto
-18 566 rmoveto
30 hlineto
50 0 50 50 vvcurveto
-30 hlineto
-50 0 -50 -50 vvcurveto
-562 vmoveto
-148 30 148 vlineto
endchar
</CharString>
<CharString name="glyph00003">
311 34 rmoveto
Expand All @@ -97,6 +97,7 @@
-38 45 73 -40 91 hhcurveto
-70 -146 rmoveto
158 860 -30 4 -158 -860 rlineto
endchar
</CharString>
</CharStrings>
</CFFFont>
Expand Down
18 changes: 18 additions & 0 deletions Tests/varLib/mutator_test.py
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Expand Up @@ -179,6 +179,24 @@ def test_varlib_mutator_CFF2(self):
expected_ttx_path = self.get_test_output(expected_ttx_name + ".ttx")
self.expect_ttx(new_font, expected_ttx_path, tables)

def test_varlib_mutator_CFF2_rounding(self):
from fontTools.pens.recordingPen import RecordingPen

varfont = TTFont(recalcBBoxes=False, recalcTimestamp=False)
varfont.importXML(self.get_test_input("TestCFF2VFRounding.ttx"))
font = make_instance(varfont, {"wght": float(600)})

charString = font["CFF2"].cff[0].CharStrings["glyph00001"]
pen = RecordingPen()
charString.draw(pen)

# Accumulated rounding errors can cause the last point of the contour to
# not to match first point, leading to rendering artifacts.
assert pen.value[0][0] == "moveTo"
assert pen.value[0][1][0] == (-219, -12)
assert pen.value[-2][0] == "curveTo"
assert pen.value[-2][1][2] == pen.value[0][1][0]


if __name__ == "__main__":
sys.exit(unittest.main())