on_pixel_picked function of interactive CameraDisplay gets called for all displays

[kosack]

Describe the bug

As found by Vincent:

When multiple CameraDisplays are plotted on different Axis objects, each with a registered "pick_event" callback, they all seem to respond to the same "pick_event", so clicking one display moves the selected pixel on the other and the callback is called once per instance.

They should be independent.

To Reproduce

from ctapipe.visualization import CameraDisplay
from ctapipe.instrument import CameraGeometry

import matplotlib.pyplot as plt

class MyCameraDisplay(CameraDisplay):
   def on_pixel_clicked(self, pix_id):
       print(f"MyCamera: {pix_id=} has value {self.image[pix_id]:.2f}")

fig, ax = plt.subplots(2,2)
geom = CameraGeometry.from_name("NectarCam")

disp1 = MyCameraDisplay(geom, ax=ax[0,0])
disp1.enable_pixel_picker()
disp2 = MyCameraDisplay(geom, ax=ax[0,1])
disp2.enable_pixel_picker()

plt.show()

When clicking a pixel in either CameraDisplay, both get updated and the on_pixel_picked() method gets called twice

Expected behavior

Each display can be clicked independently

Supporting information
If applicable, add screenshots, logs, or a traceback to help illustrate the bug.

Additional context

The relevant line is probably:

ctapipe/ctapipe/visualization/mpl_camera.py

Line 269 in 623ac86

self.axes.figure.canvas.mpl_connect("pick_event", self._on_pick)

Which should set the callback on this instance, not in general.

[maxnoe]

I think I already commented somewhere, that we should have enable_pixel_picker take a callback function, not via the currently intended inheritance

This would also solve this issue