René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Line2D can snap incorrectly and request snap(x)(y) parameters","articleBody":"### Bug report\r\n\r\n**Bug summary**\r\n\r\n`Axes.plot` produces thin lines (1, 3, ... px) which may snap incorrectly relative to `Rectangle`s depending on the `dpi` and `Axes` position, in other words, the width of the left and bottom margins. In such cases, non-snapped lines achieve the desired outcome.\r\n\r\n**Code for reproduction**\r\n\r\n```python\r\nfrom matplotlib.pyplot import figure\r\nfrom matplotlib.patches import Rectangle\r\n\r\nfig = figure(figsize=(10,10), dpi=155)\r\nax = fig.add_axes([0.09, 0.1, 0.8, 0.86])\r\nax.axis([0, 1240, 0, 1333])\r\nax.minorticks_on()\r\nax.grid(which='both', ls=':')\r\n\r\nax.add_patch(Rectangle((700,800), 200, 3, snap=True))\r\nax.add_patch(Rectangle((800,700), 3, 200, snap=True))\r\nlw = 1 * 72 / 155\r\nax.plot([890,801.5,801.5], [801.5,801.5,890], c='lime', lw=lw, snap=True)\r\nax.plot([710,801.5,801.5], [801.5,801.5,710], c='red', lw=lw, snap=False)\r\n\r\nfig.savefig(\"snap.png\")\r\n```\r\n\r\nThe `Axes` relative position of (0.09, 0.1) is chosen on purpose so that the left margin is 0.09 * 10 in * 155 dpi = 139.5 px and the bottom one is 155 px. Also note that the `Axis` are scaled to be 1 pixel : 1 unit.\r\n\r\n**Actual outcome**\r\n\r\nZoom in to view individual pixels...\r\n\r\n![snap](https://user-images.githubusercontent.com/26471497/100774828-4a2c2f80-33e1-11eb-9c82-02bd350260c8.png)\r\n\r\n**Expected outcome**\r\n\r\nThat the lime line snaps correctly in the middle of the blue `Rectangle`s. Note how the horizontal non-snapped red line works as desired.\r\n\r\n**Feature request**\r\n\r\nTo implement something equivalent to `snapx` and `snapy` following `scalex` and `scaley` trend. #15595 might change this trend though. This feature could be used to work around this issue, but I think the solutions should be independent. Will split this request into another issue if it's welcomed.\r\n\r\n**Matplotlib version**\r\n\r\n  * Operating system: Windows 10\r\n  * Matplotlib version: 3.3.3\r\n  * Matplotlib backend: module://ipykernel.pylab.backend_inline\r\n  * Python version: 3.9.0\r\n\r\nPython installed via official installer. Matplotlib installed via pip.","author":{"url":"https://github.com/alexiscoutinho","@type":"Person","name":"alexiscoutinho"},"datePublished":"2020-12-01T18:14:03.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/19054/matplotlib/issues/19054"}