René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"pdf backend displaces patches","articleBody":"I try to draw a circle in display coordinates around a point to avoid stretching when the axes are not equal. Using the pdf backend, the following code will give me a circle that is not centered on the point anymore:\r\n\r\n```python\r\n#!/usr/bin/env python\r\n# -*- coding: utf-8 -*-\r\nimport matplotlib.pyplot as plt\r\nimport matplotlib.patches as mpatches\r\nimport ipdb\r\nfig = plt.figure()\r\nax = fig.add_subplot(1,1,1)\r\n# plot two points\r\nax.plot((0.2,0.7),(0.5,0.5), \"o\")\r\nax.set_xlim((0,1))\r\n# get the display coordinates\r\nx, y = ax.transData.transform((0.2,0.5))\r\n# plot a circle around the point\r\ncircle = mpatches.Circle((x,y),50,fill=None)\r\n# add to figure\r\nfig.artists.append(circle)\r\n\r\n# save to pdf - circle will not be centered on (0.2,0.5)\r\nfig.savefig(\"displaced.pdf\")\r\n# save to pdf - circle will not be centered on (0.2,0.5)\r\nfig.savefig(\"displaced.pdf\", dpi=fig.dpi)\r\n# save to png - circle will not be centered on (0.2,0.5)\r\nfig.savefig(\"displaced.png\")\r\n# save to png - circle will be centered on (0.2,0.5)\r\nfig.savefig(\"displaced.png\", dpi=fig.dpi)\r\n# show plot - circle will be centered\r\nplt.show(block=True)\r\n```\r\n\r\nThe reason for this can be found in`FigureCanvasPdf.print_pdf()`\r\n\r\n```\r\ndef print_pdf(self, filename, **kwargs):\r\n    image_dpi = kwargs.get('dpi', 72)  # dpi to use for images\r\n    self.figure.set_dpi(72)            # there are 72 pdf points to an inch\r\n```\r\n\r\nsuch that the input dpi will be ignored and the scaling will be off at some point. It seems like `RendererPDF` can handle arbitrary dpi, as it uses a scaling factor to `72dpi`, and a change to\r\n\r\n```\r\n     self.figure.set_dpi(image_dpi)\r\n```\r\n\r\nsolved my problem. I'm not sure though if this is just a typo or a quick fix to some other problem that is not documented here. If someone can ok this, I will open a pull request.\r\n\\ Edit\r\nI guess I missunderstood the idea behind this, since I just reverted any scaling altogether. Then I don't really know, why this is happening.\r\n","author":{"url":"https://github.com/mvllngr","@type":"Person","name":"mvllngr"},"datePublished":"2014-08-12T13:40:57.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/3364/matplotlib/issues/3364"}