74 lines
2.0 KiB
Python
74 lines
2.0 KiB
Python
"""Calculate the perimeter of a glyph."""
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from __future__ import print_function, division, absolute_import
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from fontTools.misc.py23 import *
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from fontTools.pens.basePen import BasePen
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from fontTools.misc.bezierTools import splitQuadraticAtT, splitCubicAtT
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import math
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def _distance(p0, p1):
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return math.hypot(p0[0] - p1[0], p0[1] - p1[1])
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def _dot(v1, v2):
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return (v1 * v2.conjugate()).real
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def _intSecAtan(x):
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# In : sympy.integrate(sp.sec(sp.atan(x)))
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# Out: x*sqrt(x**2 + 1)/2 + asinh(x)/2
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return x * math.sqrt(x**2 + 1)/2 + math.asinh(x)/2
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class PerimeterPen(BasePen):
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def __init__(self, glyphset=None, tolerance=0.005):
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BasePen.__init__(self, glyphset)
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self.value = 0
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self._mult = 1.+1.5*tolerance # The 1.5 is a empirical hack; no math
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def _moveTo(self, p0):
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self.__startPoint = p0
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def _lineTo(self, p1):
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p0 = self._getCurrentPoint()
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self.value += _distance(p0, p1)
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def _qCurveToOne(self, p1, p2):
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# Analytical solution to the length of a quadratic bezier.
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# I'll explain how I arrived at this later.
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p0 = self._getCurrentPoint()
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_p1 = complex(*p1)
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d0 = _p1 - complex(*p0)
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d1 = complex(*p2) - _p1
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d = d1 - d0
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n = d * 1j
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scale = abs(n)
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if scale == 0.:
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self._lineTo(p2)
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return
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origDist = _dot(n,d0)
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if origDist == 0.:
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if _dot(d0,d1) > 0:
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self._lineTo(p2)
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return
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assert 0 # TODO handle cusps
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x0 = _dot(d,d0) / origDist
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x1 = _dot(d,d1) / origDist
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Len = abs(2 * (_intSecAtan(x1) - _intSecAtan(x0)) * origDist / (scale * (x1 - x0)))
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self.value += Len
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def _addCubic(self, p0, p1, p2, p3):
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arch = _distance(p0, p3)
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box = _distance(p0, p1) + _distance(p1, p2) + _distance(p2, p3)
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if arch * self._mult >= box:
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self.value += (arch + box) * .5
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else:
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for c in splitCubicAtT(p0,p1,p2,p3,.2,.4,.6,.8):
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self._addCubic(*c)
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def _curveToOne(self, p1, p2, p3):
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p0 = self._getCurrentPoint()
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self._addCubic(p0, p1, p2, p3)
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def _closePath(self):
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p0 = self._getCurrentPoint()
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if p0 != self.__startPoint:
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self.value += _distance(p0, self.__startPoint)
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