René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"gap size for contour labels is poorly estimated","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\n\r\nThe size of the gap for contour labels in contour plots is poorly estimated.  (Noted while looking at #8819).\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\nThis uses a custom \"very wide\" font to make the problem more visible: download the font at https://www.1001fonts.com/20-db-font.html, put it somewhere where font_manager will find it, and run\r\n```python\r\nfrom pylab import *\r\n# You'll need to regen your font cache first.\r\nrcParams['font.family'] = '20 db'\r\nplt.figure()\r\nx = np.arange(400).reshape((20,20))\r\nc = plt.contour(x)\r\nplt.clabel(c)\r\nplt.show()\r\n```\r\n\r\n**Actual outcome**\r\n\r\n![bad](https://user-images.githubusercontent.com/1322974/71937102-a07df780-31ab-11ea-9b37-bb5a8ed15fb0.png)\r\n\r\n**Expected outcome**\r\n\r\n![good](https://user-images.githubusercontent.com/1322974/71937106-a542ab80-31ab-11ea-92c8-11fcf41b299c.png)\r\n\r\n---\r\n\r\nThe fix is actually not that hard (that's how I gen'd the \"good\" version)\r\n```diff\r\ndiff --git a/lib/matplotlib/contour.py b/lib/matplotlib/contour.py\r\nindex bc17765c5..dd07d9f22 100644\r\n--- a/lib/matplotlib/contour.py\r\n+++ b/lib/matplotlib/contour.py\r\n@@ -236,20 +236,12 @@ class ContourLabeler:\r\n         \"\"\"\r\n         if not isinstance(lev, str):\r\n             lev = self.get_text(lev, fmt)\r\n-        lev, ismath = text.Text()._preprocess_math(lev)\r\n-        if ismath == 'TeX':\r\n-            lw, _, _ = (texmanager.TexManager()\r\n-                        .get_text_width_height_descent(lev, fsize))\r\n-        elif ismath:\r\n-            if not hasattr(self, '_mathtext_parser'):\r\n-                self._mathtext_parser = mathtext.MathTextParser('bitmap')\r\n-            img, _ = self._mathtext_parser.parse(lev, dpi=72,\r\n-                                                 prop=self.labelFontProps)\r\n-            _, lw = np.shape(img)  # at dpi=72, the units are PostScript points\r\n-        else:\r\n-            # width is much less than \"font size\"\r\n-            lw = len(lev) * fsize * 0.6\r\n-        return lw\r\n+        fig = self.ax.figure\r\n+        width = (text.Text(0, 0, lev,\r\n+                           figure=fig, fontproperties=self.labelFontProps)\r\n+                 .get_window_extent(fig.canvas.get_renderer()).width)\r\n+        width *= 72 / fig.dpi\r\n+        return width\r\n \r\n     def set_label_props(self, label, text, color):\r\n         \"\"\"Set the label properties - color, fontsize, text.\"\"\"\r\n```\r\nbut this breaks a bunch of baseline images (unsurprisingly) so I'm going to combine this with other baseline-breaking cleanups I want to do on contour... Specifically, I plan to\r\n- get rid of https://github.com/matplotlib/matplotlib/blob/262c67fad54608e1a8ee2b7c2aac8e9e5f01dba2/lib/matplotlib/contour.py#L564-L567 (which can be removed with no bad effect)\r\n- check whether we can make the default formatter of labels the same formatter as the one that would be used for a colorbar; this would allow the use of a unicode minus and other benefits listed in https://github.com/matplotlib/matplotlib/pull/12459 (see also https://github.com/matplotlib/matplotlib/pull/12473).\r\n\r\n---\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: linux\r\n  * Matplotlib version: master\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`): agg\r\n  * Python version: 38\r\n  * Jupyter version (if applicable):\r\n  * Other libraries: \r\n\r\n\u003c!--Please tell us how you installed matplotlib and python e.g., from source, pip, conda--\u003e\r\n\u003c!--If you installed from conda, please specify which channel you used if not the default--\u003e\r\n\r\n","author":{"url":"https://github.com/anntzer","@type":"Person","name":"anntzer"},"datePublished":"2020-01-07T23:15:16.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/16153/matplotlib/issues/16153"}