René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: Updating the facecolors of a collection before its first draw has no effect","articleBody":"### Bug summary\n\nCreate e.g. a pathcollection (a scatter plot) not mapping any array, but with directly set colors; then update one of the facecolors before the first draw of the collection.  This change has no effect and gets cancelled.\n\n### Code for reproduction\n\n```python\nimport matplotlib.pyplot as plt\r\n\r\nsc1 = plt.scatter([0, 1, 2], [0, 1, 2], c=[\"r\", \"g\", \"b\"])\r\nsc2 = plt.scatter([0, 1, 2], [2, 3, 4], c=[\"r\", \"g\", \"b\"])\r\n# Update sc1 before the first draw.\r\nsc1.get_facecolors()[2] = (0, 0, 0, 1)  # i.e. black.\r\nplt.gcf().canvas.draw()\r\n# Update sc2 after the first draw.\r\nsc2.get_facecolors()[2] = (0, 0, 0, 1)  # i.e. black\r\n\r\nplt.show()\n```\n\n\n### Actual outcome\n\n![test](https://user-images.githubusercontent.com/1322974/202309814-0d84ede5-0447-4f39-8c6b-e251761f2112.png)\r\nNote that the third point of sc1 is incorrectly blue, whereas the third point of sc2 is correctly black.\n\n### Expected outcome\n\nBoth third points are black.\n\n### Additional information\n\nFirst noted by @chahak13 in https://github.com/matplotlib/matplotlib/pull/24474#discussion_r1024536389.\r\nI haven't done a full bisect but did check that this broke at some point between 3.3.4 and 3.4.0, and I suspect #18480 introduced the issue (in the changes related to update_scalarmappable); attn @efiring.\n\n### Operating system\n\nfedora37\n\n### Matplotlib Version\n\n3.7.0.dev538+g9b4985e185\n\n### Matplotlib Backend\n\nqtagg\n\n### Python version\n\n3.10\n\n### Jupyter version\n\nENOSUCHLIB\n\n### Installation\n\ngit checkout","author":{"url":"https://github.com/anntzer","@type":"Person","name":"anntzer"},"datePublished":"2022-11-16T22:41:46.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/24479/matplotlib/issues/24479"}