AngledMarginPen._curveToOne fails

[LettError]

Calling AngledMarginPen with a round shape (see example) causes a traceback.

This is a short script that gets to the problem right away. First self._start and self.currentPoint to are initialised to None.

Then _moveTo sets self._start and self.currentPoint to a point. Off to a good start!

Let's add a curve point with _curveToOne.

So_curveToOne calls _addMoveTo which sets self.currentPoint back to None. Oh no!

Following _curveToOne calls getCubicPoint with currentPoint as argument and getCubicPoint tries to split it.

I'm not sure what the _addMoveTo mechanism tries to achieve?

    amp = AngledMarginPen({}, 685, -20)
    amp._moveTo((320, 742))
    amp._curveToOne((345, 742), (358, 725), (352, 696))

Traceback (most recent call last):
  File "angledMarginPen.py", line 166, in <module>
  File "angledMarginPen.py", line 164, in testCurveIssue
  File "angledMarginPen.py", line 59, in _curveToOne
  File "angledMarginPen.py", line 28, in _getAngled
TypeError: 'NoneType' object is not subscriptable

If you don't trust the example calling private methods, this is a longer version if you want to see curveTo rather than _curveTo.

from fontParts.fontshell import RGlyph
testGlyph = RGlyph()
testGlyph.name = "testGlyph"
testGlyph.width = 685
pen = testGlyph.getPen()
pen.moveTo((320, 742))
pen.curveTo((345, 742), (358, 725), (352, 696))
pen.curveTo((347, 673), (328, 665), (310, 665))
pen.curveTo((287, 665), (273, 684), (280, 709))
pen.curveTo((285, 731), (303, 742), (320, 742))
pen.closePath()

amp = AngledMarginPen({}, 685, -20)
testGlyph.draw(amp)


Traceback (most recent call last):
  File "angledMarginPen.py", line 171, in <module>
  File "angledMarginPen.py", line 166, in testCurveIssue
  File "/Users/erik/code/fontParts/Lib/fontParts/base/glyph.py", line 630, in draw
  File "/Users/erik/code/fontParts/Lib/fontParts/base/contour.py", line 172, in draw
  File "/Users/erik/code/fontParts/Lib/fontParts/base/contour.py", line 180, in _draw
  File "/Users/erik/code/fontParts/Lib/fontParts/base/contour.py", line 188, in drawPoints
  File "/Users/erik/code/fontParts/Lib/fontParts/base/contour.py", line 213, in _drawPoints
  File "/Applications/RoboFont_4.5b.app/Contents/Resources/lib/python3.12/fontTools/pens/pointPen.py", line 173, in endPath
  File "/Applications/RoboFont_4.5b.app/Contents/Resources/lib/python3.12/fontTools/pens/pointPen.py", line 250, in _flushContour
  File "/Applications/RoboFont_4.5b.app/Contents/Resources/lib/python3.12/fontTools/pens/basePen.py", line 339, in curveTo
  File "angledMarginPen.py", line 59, in _curveToOne
  File "angledMarginPen.py", line 28, in _getAngled
TypeError: 'NoneType' object is not subscriptable

[justvanrossum]

I'm trying to understand the intention of the code, but I can't figure it out.

_curveToOne() calls self._addMoveTo(), which sets self.currentPoint to None, but _curveToOne() then uses self.currentPoint for a call to getCubicPoint(), which fails on this None point it is receiving.

[LettError]

Could _addMoveTo be for open paths?

[typemytype]

I guess pens behaved differently a long time ago... so finally after 13 years it breaks... https://github.com/robotools/robofab/blob/master/Lib/robofab/pens/angledMarginPen.py

will fix that pen!

[LettError]

Thanks!