René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Multicursor disappears when not moving on nbagg with useblit=False + burns CPU","articleBody":"\u003c!--To help us understand and resolve your issue, please fill out the form to the best of your ability.--\u003e\r\n\u003c!--You can feel free to delete the sections that do not apply.--\u003e\r\n\r\n### Bug report\r\n\r\n**Bug summary**\r\nWhen on the nbagg backend if you stop moving the mouse the multicursor will disappear. The same example works fine on the qt backend.\r\n\r\nAdditionally I noticed that when I add the multicursor my cpu usage jumps and the kernel busy indicator constantly flashes on and off. \r\n\r\nShowing the plot without the multicursor:\r\n![image](https://user-images.githubusercontent.com/10111092/109886513-28e01700-7c4e-11eb-8aac-d8a18832f787.png)\r\nand with the multicursor (just displaying, not interacting with the plot):\r\n\r\n![image](https://user-images.githubusercontent.com/10111092/109886579-490fd600-7c4e-11eb-94d8-ce4d9425559f.png)\r\nThat usage is pretty stable and my laptop's fan goes wild.\r\n\r\nThe issue with the dissappearing was originally noticed by @ipcoder in https://github.com/matplotlib/ipympl/issues/306\r\n\r\n**Code for reproduction**\r\n\r\n\u003c!--A minimum code snippet required to reproduce the bug.\r\nPlease make sure to minimize the number of dependencies required, and provide\r\nany necessary plotted data.\r\nAvoid using threads, as Matplotlib is (explicitly) not thread-safe.--\u003e\r\n\r\n```python\r\n%matplotlib nbagg\r\nimport numpy as np\r\nimport matplotlib.pyplot as plt\r\nfrom matplotlib.widgets import MultiCursor\r\n\r\nt = np.arange(0.0, 2.0, 0.01)\r\ns1 = np.sin(2*np.pi*t)\r\ns2 = np.sin(4*np.pi*t)\r\n\r\nfig, (ax1, ax2) = plt.subplots(2, sharex=True)\r\nax1.plot(t, s1)\r\nax2.plot(t, s2)\r\n\r\nmulti = MultiCursor(fig.canvas, (ax1, ax2), color='r', lw=1, useblit=False)\r\nplt.show()\r\n```\r\n\r\n**Actual outcome**\r\n\r\n![Peek 2021-03-03 18-12](https://user-images.githubusercontent.com/10111092/109885329-54fa9880-7c4c-11eb-9caa-f765dda6f729.gif)\r\n\r\nand the high CPU usage\r\n\r\n\r\n**Expected outcome**\r\nRed line doesn't disappear + my CPU doesn't get crushed.\r\n\r\n\r\n\u003c!--A description of the expected outcome from the code snippet--\u003e\r\n\u003c!--If this used to work in an earlier version of Matplotlib, please note the version it used to work on--\u003e\r\n\r\n**Matplotlib version**\r\n\u003c!--Please specify your platform and versions of the relevant libraries you are using:--\u003e\r\n  * Operating system: Ubuntu\r\n  * Matplotlib version (`import matplotlib; print(matplotlib.__version__)`): '3.3.4.post2456+gfd23bb238'\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`): nbagg\r\n  * Python version: '3.9.1 | packaged by conda-forge | (default, Jan 26 2021, 01:34:10) \\n[GCC 9.3.0]'\r\n  * Jupyter version (if applicable): Notebook 6.2.0 - IPython 7.20.0\r\n\r\ndev instlal of maptlotlib + conda-forge for the others \r\n","author":{"url":"https://github.com/ianhi","@type":"Person","name":"ianhi"},"datePublished":"2021-03-03T23:33:00.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":13},"url":"https://github.com/19633/matplotlib/issues/19633"}