René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: Draggable Legend is out of control unless it has a picker set.","articleBody":"### Bug summary\n\nThe draggable legend as described in the Documentation (https://matplotlib.org/stable/gallery/event_handling/legend_picking.html) is behaving in an unexpected manner. \n\nClick and drag the mouse when the _cursor is far away from the legend_ moves the legend. \n\nFrom a usability point of view it would make sense that only when the cursor is over the legend that the legend can be moved by dragging the mouse. \n\nSolution (?). It appears that the `Legend`, being an `Artist`, has a picker_function that is not returning a value: ` print(legend.get_picker()` gives for example `\u003cfunction DraggableBase._picker at 0x7f95a0151bc0\u003e`. \nBy setting a picker with any value - apart from `None`, which  kills draggability - results in expected draggability behavior. \nMaybe a call `self.set_picker(1)` or so during initialization of a draggable legend could solve this issue?\n\n### Code for reproduction\n\n```Python\n#!/usr/bin/env python3\n#\nimport matplotlib.pyplot as plt\nimport numpy as np\n\nfrom matplotlib.text import Text\n\nt = np.linspace(0, 1)\ny1 = 2 * np.sin(2 * np.pi * t)\ny2 = 4 * np.sin(2 * np.pi * 2 * t)\n\nfig, ax = plt.subplots()\ntitle = ax.set_title('Click this title once to control draggable legend')\ntitle.set_picker(5)\n(line1, ) = ax.plot(t, y1, lw=2, label='1 Hz')\n(line2, ) = ax.plot(t, y2, lw=2, label='2 Hz')\nleg = ax.legend(fancybox=True, shadow=True)\n#leg.set_picker(None)  # no effect on set_draggable artefact\n\nlines = [line1, line2]\nmap_legend_to_ax = {}  # Will map legend lines to original lines.\n\npickradius = 5  # Points (Pt). How close the click needs to be to trigger an event.\n\nfor legend_line, ax_line in zip(leg.get_lines(), lines):\n    legend_line.set_picker(pickradius)  # Enable picking on the legend line.\n    map_legend_to_ax[legend_line] = ax_line\n\n\ndef on_pick(event):\n    # On the pick event, find the original line corresponding to the legend\n    # proxy line, and toggle its visibility.\n    legend_line = event.artist\n\n    if isinstance(event.artist, Text):\n            leg.set_picker(0)\n            print(f\"Picker set on legend: {leg.get_picker()}\\n\"\n            \"Now, only mouse_press on legend makes it move.\")\n\n\n    # Do nothing if the source of the event is not a legend line.\n    if legend_line not in map_legend_to_ax:\n        return\n\n    ax_line = map_legend_to_ax[legend_line]\n    visible = not ax_line.get_visible()\n    ax_line.set_visible(visible)\n    # Change the alpha on the line in the legend, so we can see what lines\n    # have been toggled.\n    legend_line.set_alpha(1.0 if visible else 0.2)\n    fig.canvas.draw()\n\n#leg.set_picker(None) # no effect on set_draggable artefact\nfig.canvas.mpl_connect('pick_event', on_pick)\n#leg.set_picker(None) # no effect on set_draggable artefact\n\n# Works even if the legend is draggable. This is independent from picking legend lines.\nleg.set_draggable(True)\n#leg.set_picker(None) # kills set_draggable\n#leg.set_draggable(True) # cannot restore set_draggable\n#leg.set_picker(0) # creates expected draggable-legend-behaviour\n\nprint (f\"Legend picker: {leg.get_picker()}; \\n\"\n    \"legend can be moved by mouse_drag far away from legend.\")\nplt.show()\n```\n\n### Actual outcome\n\nDrag the mouse-pointer (press button + move) anywhere over the canvas outwith the legend and the legend will move as well.\n\n### Expected outcome\n\nDrag the mouse over the canvas outwith the legend and the legend will NOT move. The legend will only move when dragged by the mouse directly.\n\n### Additional information\n\n_No response_\n\n### Operating system\n\nSlackware linux, 64-bit, current\n\n### Matplotlib Version\n\n3.10.3\n\n### Matplotlib Backend\n\nTkAgg\n\n### Python version\n\n3.12.11\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nfrom source (.tar.gz)","author":{"url":"https://github.com/brobr","@type":"Person","name":"brobr"},"datePublished":"2025-07-13T16:07:07.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/30303/matplotlib/issues/30303"}