[MNT]: Draggable legend gets stuck on cursor after scroll event

Summary

Draggable legend gets stuck to cursor after scrolling while hovering the artist. To 'unstick' it, it is necessary to left click. I believe the expected behavior is to only drag the legend while holding the left mouse button. If that is not the case, please close this issue.

Proposed fix

Sample code:

import matplotlib.pyplot as plt

plt.plot([],[], label='scroll over me, then move the cursor')
plt.legend(draggable=True)
plt.show()

I believe the issue is that the class DraggableBase (at line 1425 of matplotlib/offsetbox.py) uses a 'pick' event to grab the artist, which I believe includes scrolling events. It might be possible to return from a false positive pick by checking that the pick event is a mouse click instead of scrolling at DraggableBase.on_pick. Another alternative is to change the pick event to a button_press event.

Perhaps related to #29066 too?

I am not sure to be honest. I don't know much about the backends. But the problem described doesn't appear to be the same. In fact I tried implementing my solution inside offsetbox.py and it worked as predicted. Scroll events no longer make legend stick to cursor.

This is the proposed modification (first 3 lines of DraggableBase.on_pick):

def on_pick(self, evt):
       # Return if mouseevent is a scroll (this is the modification)
       if evt.mouseevent.button in ('up','down'):
           return
       if self._check_still_parented() and evt.artist == self.ref_artist:
           self.mouse_x = evt.mouseevent.x
           self.mouse_y = evt.mouseevent.y
           self.got_artist = True
           if self._use_blit:
               self.ref_artist.set_animated(True)
               self.canvas.draw()
               self.background = \
                   self.canvas.copy_from_bbox(self.ref_artist.figure.bbox)
               self.ref_artist.draw(
                   self.ref_artist.figure._get_renderer())
               self.canvas.blit()
           self.save_offset()

Oh, I see. OK, I agree your proposed patch seems reasonable (perhaps rather check evt.name == "scroll_event", which is more explicit, though).

Hi can I work on solving this issue?

Is the thread author responsible for giving permission? If so, yes.

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[MNT]: Draggable legend gets stuck on cursor after scroll event #29142

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[MNT]: Draggable legend gets stuck on cursor after scroll event #29142

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anntzer commented on Nov 15, 2024

p479h commented on Nov 16, 2024

anntzer commented on Nov 21, 2024

Kaustbh commented on Dec 3, 2024

p479h commented on Dec 4, 2024

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