8000 [_g_l_y_f] fix float precision loss in GlyphCoordinates by anthrotype · Pull Request #964 · fonttools/fonttools · GitHub
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[_g_l_y_f] fix float precision loss in GlyphCoordinates #964

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Merged
merged 2 commits into from
May 16, 2017
Merged

[_g_l_y_f] fix float precision loss in GlyphCoordinates #964

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1c9198e
[_g_l_y_f] add test for GlyphCoordinates' float precision loss issue …
May 16, 2017
71486bc
[_g_l_y_f] use 'd' instead of 'f' as array.array typecode in GlyphCoo…
May 16, 2017
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8000
4 changes: 2 additions & 2 deletions Lib/fontTools/ttLib/tables/_g_l_y_f.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1170,13 +1170,13 @@ def array(self):
return self._a

def isFloat(self):
return self._a.typecode == 'f'
return self._a.typecode == 'd'

def _ensureFloat(self):
if self.isFloat():
return
# The conversion to list() is to work around Jython bug
self._a = array.array("f", list(self._a))
self._a = array.array("d", list(self._a))

def _checkFloat(self, p):
if self.isFloat():
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10 changes: 10 additions & 0 deletions Tests/ttLib/tables/_g_l_y_f_test.py
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Expand Up @@ -143,3 +143,13 @@ def test__bool__(self):
assert bool(g) == True
g = GlyphCoordinates([(0,.5), (0,0)])
assert bool(g) == True

def test_double_precision_float(self):
# https://github.com/fonttools/fonttools/issues/963
afloat = 242.50000000000003
g = GlyphCoordinates([(afloat, 0)])
g.toInt()
# this would return 242 if the internal array.array typecode is 'f',
# since the Python float is truncated to a C float.
# when using typecode 'd' it should return the correct value 243
assert g[0][0] == round(afloat)
0