Lib/fontTools/pens/areaPen.py

"""Calculate the area of a glyph."""

from __future__ import print_function, division, absolute_import
from fontTools.misc.py23 import *
from fontTools.pens.basePen import BasePen


class AreaPen(BasePen):

	def __init__(self, glyphset=None):
		BasePen.__init__(self, glyphset)
		self.value = 0

	def _moveTo(self, p0):
		"""Remember the first point in this contour, in case it's closed. Also
		set the initial value for p0 in this contour, which will always refer to
		the most recent point.
		"""
		self._p0 = self._startPoint = p0

	def _lineTo(self, p1):
		"""Add the signed area beneath the line from the latest point to this
		one. Signed areas cancel each other based on the horizontal direction of
		the line.
		"""
		x0, y0 = self._p0
		x1, y1 = p1
		self.value -= (x1 - x0) * (y1 + y0) * .5
		self._p0 = p1

	def _qCurveToOne(self, p1, p2):
		"""Add the signed area of this quadratic curve.
		https://github.com/Pomax/bezierinfo/issues/44
		"""
		p0 = self._p0
		x0, y0 = p0[0], p0[1]
		x1, y1 = p1[0] - x0, p1[1] - y0
		x2, y2 = p2[0] - x0, p2[1] - y0
		self.value -= (x2 * y1 - x1 * y2) / 3
		self._lineTo(p2)
		self._p0 = p2

	def _curveToOne(self, p1, p2, p3):
		"""Add the signed area of this cubic curve.
		https://github.com/Pomax/bezierinfo/issues/44
		"""
		p0 = self._p0
		x0, y0 = p0[0], p0[1]
		x1, y1 = p1[0] - x0, p1[1] - y0
		x2, y2 = p2[0] - x0, p2[1] - y0
		x3, y3 = p3[0] - x0, p3[1] - y0
		self.value -= (
				x1 * (   -   y2 -   y3) +
				x2 * (y1        - 2*y3) +
				x3 * (y1 + 2*y2       )
			      ) * 0.15
		self._lineTo(p3)
		self._p0 = p3

	def _closePath(self):
		"""Add the area beneath this contour's closing line."""
		self._lineTo(self._startPoint)
		del self._p0, self._startPoint

	def _endPath(self):
		"""Area is not defined for open contours.
		Single-point open contours, which often represent anchors, are allowed.
		"""
		if self._p0 != self._startPoint:
			raise NotImplementedError
		del self._p0, self._startPoint