97 lines
3.9 KiB
Python
97 lines
3.9 KiB
Python
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from fontTools.misc.arrayTools import pairwise
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from fontTools.pens.filterPen import ContourFilterPen
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__all__ = ["reversedContour", "ReverseContourPen"]
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class ReverseContourPen(ContourFilterPen):
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"""Filter pen that passes outline data to another pen, but reversing
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the winding direction of all contours. Components are simply passed
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through unchanged.
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Closed contours are reversed in such a way that the first point remains
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the first point.
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"""
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def __init__(self, outPen, outputImpliedClosingLine=False):
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super().__init__(outPen)
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self.outputImpliedClosingLine = outputImpliedClosingLine
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def filterContour(self, contour):
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return reversedContour(contour, self.outputImpliedClosingLine)
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def reversedContour(contour, outputImpliedClosingLine=False):
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"""Generator that takes a list of pen's (operator, operands) tuples,
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and yields them with the winding direction reversed.
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"""
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if not contour:
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return # nothing to do, stop iteration
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# valid contours must have at least a starting and ending command,
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# can't have one without the other
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assert len(contour) > 1, "invalid contour"
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# the type of the last command determines if the contour is closed
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contourType = contour.pop()[0]
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assert contourType in ("endPath", "closePath")
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closed = contourType == "closePath"
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firstType, firstPts = contour.pop(0)
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assert firstType in ("moveTo", "qCurveTo"), (
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"invalid initial segment type: %r" % firstType
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)
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firstOnCurve = firstPts[-1]
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if firstType == "qCurveTo":
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# special case for TrueType paths contaning only off-curve points
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assert firstOnCurve is None, "off-curve only paths must end with 'None'"
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assert not contour, "only one qCurveTo allowed per off-curve path"
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firstPts = (firstPts[0],) + tuple(reversed(firstPts[1:-1])) + (None,)
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if not contour:
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# contour contains only one segment, nothing to reverse
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if firstType == "moveTo":
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closed = False # single-point paths can't be closed
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else:
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closed = True # off-curve paths are closed by definition
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yield firstType, firstPts
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else:
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lastType, lastPts = contour[-1]
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lastOnCurve = lastPts[-1]
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if closed:
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# for closed paths, we keep the starting point
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yield firstType, firstPts
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if firstOnCurve != lastOnCurve:
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# emit an implied line between the last and first points
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yield "lineTo", (lastOnCurve,)
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contour[-1] = (lastType, tuple(lastPts[:-1]) + (firstOnCurve,))
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if len(contour) > 1:
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secondType, secondPts = contour[0]
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else:
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# contour has only two points, the second and last are the same
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secondType, secondPts = lastType, lastPts
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if not outputImpliedClosingLine:
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# if a lineTo follows the initial moveTo, after reversing it
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# will be implied by the closePath, so we don't emit one;
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# unless the lineTo and moveTo overlap, in which case we keep the
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# duplicate points
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if secondType == "lineTo" and firstPts != secondPts:
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del contour[0]
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if contour:
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contour[-1] = (lastType, tuple(lastPts[:-1]) + secondPts)
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else:
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# for open paths, the last point will become the first
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yield firstType, (lastOnCurve,)
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contour[-1] = (lastType, tuple(lastPts[:-1]) + (firstOnCurve,))
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# we iterate over all segment pairs in reverse order, and yield
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# each one with the off-curve points reversed (if any), and
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# with the on-curve point of the following segment
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for (curType, curPts), (_, nextPts) in pairwise(contour, reverse=True):
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yield curType, tuple(reversed(curPts[:-1])) + (nextPts[-1],)
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yield "closePath" if closed else "endPath", ()
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