[Bug]: canvas pick events not working when Axes belongs to a subfigure

[ndeadly]

Bug summary

When an axis is added to a subfigure, rather than the root figure, canvas pick events are no longer received for that axis.

Code for reproduction

import matplotlib.pyplot as plt
import matplotlib.gridspec as mgridspec
import numpy as np

def on_pick(evt):
    print('pick event!')

fig = plt.figure()
gs = mgridspec.GridSpec(1, 1)

# Pick events working
#ax = fig.add_subplot(gs[0, 0])

# Pick events not working
subfig = fig.add_subfigure(gs[0, 0])
ax = subfig.add_subplot(1, 1, 1)

ax.plot(np.random.random(10), np.random.random(10), marker='.', linestyle='none', picker=5)

fig.canvas.mpl_connect('pick_event', on_pick)
plt.show()

Actual outcome

No output.

Expected outcome

The following should be displayed on the console when one of the markers is clicked.

>> pick event!

Additional information

No response

Operating system

Windows 10

Matplotlib Version

3.7.1

Matplotlib Backend

Qt5Agg

Python version

3.8.10

Jupyter version

No response

Installation

pip

[tacaswell]

Thank you for the very clear report @ndeadly ! I can confirm that this is a bug.

My suspicion is that in the pick function from Figure (which might be inherited from Artist) it is not correctly offering pick events to the SubFigures of the Figure.

Tasks:

• trace through the code for pick events in Figure and verify or disprove my theory
• if my theory is right, offer the event to all of the SubFigures
• [bonus] add a test. We have some machinery for creating synthetic mouse events. Either make that work or show it will me order of magnitude more code to write a test harness than the fix was.

Labeling as good first issue because it is a clear bug and there is no API design here (the pick event should fire!), but medium as it will require walking through the event handling stack and reasoning through some OO code.

[QuLogic]

Small note; this is about Axes, not Axis.

[QuLogic]

My suspicion is that in the pick function from Figure (which might be inherited from Artist) it is not correctly offering pick events to the SubFigures of the Figure.

I think this is correct, but maybe not for an expected reason; Figure inherits from Artist, which loops through self.get_children() and offers the event to children whose .axes attribute matches the event's Axes or any child if either is None. And SubFigure, like Figure, does not have a parent Axes, but it does have an axes attribute which is a list of Axes children. So this never matches the event Axes or None, and SubFigures never get picked.

[tsabbir96]

@tacaswell @QuLogic Hi guys, do you mind if I take a look at the issue? I would like to offer my help in solving this.

[tacaswell]

@tsabbir96 Yes, we do not assign issues, if there is not a linked PR assume the issue is up for grabs and you are free to work on it.

[turnipseason]

Hi, @tsabbir96. Are you still working on this?

[klorine28]

Hello @tacaswell I think I came up with a possible solution should I post it here or do I do a pull request? if it's the latter where in the documentation should I look in? this would be my first issue.

[rcomer]

Hi @klorine28 please go ahead and make a pull request. Our contributors' guide is here:
https://matplotlib.org/devdocs/devel/index.html

[klorine28]

sorry to ask but in what branch should I modify the code? i know its not main but I am unsure on wich one I should do it

[rcomer]

@klorine28 see our "Workflow" guide 😀
https://matplotlib.org/devdocs/devel/development_workflow.html

[QuLogic]

This has been fixed by #27343.