annotation connectionstyle and width, headwidth compatibility issue

[jiadongdan]

Some connectionstyle can not work!!!

See code below:

fig, ax = plt.subplots(1, 1, figsize=(7.2, 7.2))
start = (0.1, 0.1)
end = (0.5, 0.5)
connectionstyle='arc3, rad=1'
#connectionstyle='angle,angleA=-90,angleB=10,rad=5' #this not working

ax.annotate("",
            xy=end, xycoords='data',
            xytext=start, textcoords='data',
            arrowprops=dict(#arrowstyle="->, head_length=1, head_width=1",
                            width=10,headwidth=30,
                            color="0.5",
                            shrinkA=5, shrinkB=5,
                            patchA=None,
                            patchB=None,
                            connectionstyle=connectionstyle,
                            ),)

This code snipet works fine. However, if I change connectionstyle to "angle,angleA=-90,angleB=10,rad=5", it just does not work. Not sure what is wrong.

matplotlib version: 3.0.3

[jklymak]

Traceback (most recent call last):
  File "/Users/jklymak/matplotlib/lib/matplotlib/backends/backend_qt5.py", line 501, in _draw_idle
    self.draw()
  File "/Users/jklymak/matplotlib/lib/matplotlib/backends/backend_agg.py", line 388, in draw
    self.figure.draw(self.renderer)
  File "/Users/jklymak/matplotlib/lib/matplotlib/artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "/Users/jklymak/matplotlib/lib/matplotlib/figure.py", line 1716, in draw
    renderer, self, artists, self.suppressComposite)
  File "/Users/jklymak/matplotlib/lib/matplotlib/image.py", line 135, in _draw_list_compositing_images
    a.draw(renderer)
  File "/Users/jklymak/matplotlib/lib/matplotlib/artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "/Users/jklymak/matplotlib/lib/matplotlib/axes/_base.py", line 2670, in draw
    mimage._draw_list_compositing_images(renderer, self, artists)
  File "/Users/jklymak/matplotlib/lib/matplotlib/image.py", line 135, in _draw_list_compositing_images
    a.draw(renderer)
  File "/Users/jklymak/matplotlib/lib/matplotlib/artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "/Users/jklymak/matplotlib/lib/matplotlib/text.py", line 2369, in draw
    self.arrow_patch.draw(renderer)
  File "/Users/jklymak/matplotlib/lib/matplotlib/patches.py", line 4303, in draw
    path, fillable = self.get_path_in_displaycoord()
  File "/Users/jklymak/matplotlib/lib/matplotlib/patches.py", line 4287, in get_path_in_displaycoord
    self.get_mutation_aspect())
  File "/Users/jklymak/matplotlib/lib/matplotlib/patches.py", line 3250, in __call__
    return self.transmute(path, mutation_size, linewidth)
  File "/Users/jklymak/matplotlib/lib/matplotlib/patches.py", line 3717, in transmute
    x0, y0, x1, y1, x2, y2 = self.ensure_quadratic_bezier(path)
  File "/Users/jklymak/matplotlib/lib/matplotlib/patches.py", line 3202, in ensure_quadratic_bezier
    "'path' is not a valid quadratic Bezier curve")
ValueError: 'path' is not a valid quadratic Bezier curve

[github-actions]

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[ksunden]

I think that this is actually correct that it is unable to work and should raise, however I think the work is to make the error message more understandable (and potentially erroring before draw is called, but that is less necessary). While "not a valid quadratic Bezier curve" is at least in some sense accurate and the proximal cause of the incompatibility, it is not useful to a user who asked for an arrow to be drawn.

The short version is that the default arrow style is "simple", which can only work with a subset of connection styles, such as arc3 or angle3.

Setting the arrow style to e.g. -> (or pretty much any of the more pictoral keys, i.e. all except "simple", "fancy", or "wedge") will fix it.

The annotate docstring for the arrowprops arg gets at this behavior by saying:

For historical reasons there are two different ways to specify arrows, "simple" and "fancy":

Simple arrow:

If arrowprops does not contain the key 'arrowstyle' the allowed keys are:

<table removed for brevity, but notably "connectionstyle" is absent>

...

Fancy arrow:

This is used if 'arrowstyle' is provided in the arrowprops.

Valid keys are the following FancyArrowPatch parameters:

<table removed for brevity, but notably "connectionstyle" is present>

Technically, there are some options for "connectionstyle" that will work, and they do still get passed through to FancyArrowPatch so not sure disallowing it fully would be advisable.