René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Type 42 chars beyond BMP not displayed in PDF","articleBody":"### Bug report\r\n\r\n**Bug summary**\r\n\r\nCharacters from beyond the Basic Multilingual Plane (BMP) in Unicode are not displayed in PDFs with Type 42 fonts. Characters beyond the BMP have a code point greater than 65535 and cannot be encoded in a fixed-size 2-byte encoding, such as the obsolete UCS-2. My understanding is that the CID maps still use such an encoding and cannot handle code points beyond that.\r\n \r\nIn the case of the `m` in STIX Sans, it's implemented via a virtual font embedded in the base font with chars shifted to higher code points, here code point 120366.\r\n\r\n**Code for reproduction**\r\n```python\r\nimport matplotlib.pyplot as plt\r\nfrom matplotlib import rcParams\r\n\r\nrcParams[\"pdf.fonttype\"] = 42\r\nrcParams[\"mathtext.fontset\"] = \"stixsans\"\r\n\r\nplt.text(0.5, 0.5, \"Mass $m$ \\U00010308\")\r\nplt.savefig(\"beyond_bmp.pdf\")\r\n```\r\n\r\n**Actual outcome**\r\n\r\n![beyond_bmp_pdf](https://user-images.githubusercontent.com/12832470/125108935-fbffad00-e0e2-11eb-8998-a776d43921ac.png)\r\n[beyond_bmp.pdf](https://github.com/matplotlib/matplotlib/files/6792729/beyond_bmp.pdf)\r\n\r\n**Expected outcome**\r\n![beyond_bmp](https://user-images.githubusercontent.com/12832470/125109022-19347b80-e0e3-11eb-9640-763025ba572d.png)\r\n\r\n**Possible solutions**\r\nWe could take a similar approach as we did for Type 3 fonts. There any char\u003e255 is embedded via an `XObject` and not via the font directly. So, here the solution would be to use `XObjects` if the char\u003e65535 in text and math mode.\r\n\r\nI have a local, modified version of matplotlib based on https://github.com/matplotlib/matplotlib/pull/20615 which implements this approach. It extends the use of `_font_supports_char` and restricts the supported range for Type 42 to \u003c=65535. I can polish this local fix into a PR if people what to go this route.\r\n\r\n**Matplotlib version**\r\n\r\n  * Operating system: Debian 11\r\n  * Matplotlib version (`import matplotlib; print(matplotlib.__version__)`):  3.4.2\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`): TkAgg (but I assume pdf)\r\n  * Python version: 3.9.2\r\n  * Matplotlib installed with pip in a virtual env\r\n","author":{"url":"https://github.com/sauerburger","@type":"Person","name":"sauerburger"},"datePublished":"2021-07-09T16:39:09.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/20616/matplotlib/issues/20616"}