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joinstyle is not respected for FancyArrowPatch (either the path or the arrow heads) #13641

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david-hoffman opened this issue Mar 9, 2019 · 3 comments · Fixed by #13647
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joinstyle is not respected for FancyArrowPatch (either the path or the arrow heads) #13641

david-hoffman opened this issue Mar 9, 2019 · 3 comments · Fixed by #13647
Milestone
v3.2.0

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@david-hoffman
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Bug report

Bug summary

joinstyle is not respected for FancyArrowPatch (either the path or the arrow heads)

Code for reproduction

import matplotlib as mpl
import matplotlib.pyplot as plt

# high dpi so you can see the difference
fig, ax = plt.subplots(dpi=600)

# iterate through styles
for i, js in enumerate(("miter", "round", "bevel"), start=1):
    arrow_head = mpl.patches.ArrowStyle.CurveFilledAB(head_length=4, head_width=2)
    connection = mpl.patches.ConnectionStyle.Bar(fraction=0, angle=-90)
    double_arrow = mpl.patches.FancyArrowPatch((0.1 * i, 1 - 0.1), (1 - 0.1, 0.1 * i), linewidth=2,
                                       arrowstyle=arrow_head, connectionstyle=connection, joinstyle=js)
    ax.add_patch(double_arrow)

Actual outcome

image

Expected outcome

Different join styles for each line (including arrow heads)

Matplotlib version

  • Operating system: Windows 10
  • Matplotlib version: 3.0.2
  • Matplotlib backend (print(matplotlib.get_backend())): Qt5Agg
  • Python version:
Python 3.7.2 (default, Feb 21 2019, 17:35:59) [MSC v.1915 64 bit (AMD64)]
Type 'copyright', 'credits' or 'license' for more information
IPython 7.2.0 -- An enhanced Interactive Python. Type '?' for help.

I installed with the default conda channel.
@ImportanceOfBeingErnest
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ImportanceOfBeingErnest commented Mar 10, 2019 •
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The joinstyle and capstyle are fixed for FancyArrowPatch.

matplotlib/lib/matplotlib/patches.py

Lines 4287 to 4289 in 21f1355

# FancyArrowPatch has traditionally forced the capstyle and joinstyle.
with cbook._setattr_cm(self, _capstyle='round', _joinstyle='round'), \
self._bind_draw_path_function(renderer) as draw_path:

I don't know why that is the case. If we remove that line the result would look like this:

image

Is that what you're expecting? Would someone know why that got fixed in the first place?

@ImportanceOfBeingErnest
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Ok, here is the deal (in a comment by @anntzer):

Yes, ignoring the capstyle was probably a long-standing bug [..] but changing that would result in changes in the baseline images [..]. I'll leave this as it is until someone actually complains or we have some othe reason to change the baseline images.

Actually, I don't quite see why we can't keep "round" as default - in that way no baseline images need to change and it remains backwards compatible - but at the same time allow for user input to change it.

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@ImportanceOfBeingErnest
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A possible fix is at #13647, no changes are made to the defaults and tests pass as they are.

@QuLogic QuLogic added this to the v3.2.0 milestone Mar 14, 2019
@mapfiable mapfiable mentioned this issue Jan 28, 2022
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Fix FancyArrowPatch joinstyle ImportanceOfBeingErnest/matplotlib
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@QuLogic @david-hoffman @ImportanceOfBeingErnest