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[Bug]: Saving as an SVG and PDF produce different outputs with Latex characters, with wrong character sizing #29791
Description
Bug summary
When saving certain outputs using Latex rendering as an SVG, it produces wrong outputs. Using plt.show() it renders correctly, and it works for saving as a PDF, but saving the output as a SVG math environment characters can render in the wrong size (see attached screenshots.)
Code for reproduction
from pathlib import Path
import pandas as pd
import matplotlib.pyplot as plt
import scienceplots
BASE_PATH = Path(__file__).parent
DATA_PATH = BASE_PATH / "ion_ranges.csv"
plt.style.use(['science', 'latex-siunitx'])
dat = pd.read_csv(DATA_PATH)
plt.plot(dat["energy"], dat["projected_range_um"], marker="o", linestyle="-")
plt.xlabel("Energy (keV)")
plt.ylabel(r"Projected Range (\si{\um})")
plt.tight_layout()
plt.savefig(BASE_PATH / "ion_ranges_plot.pdf")Actual outcome
Expected outcome
Additional information
No response
Operating system
No response
Matplotlib Version
3.10.1
Matplotlib Backend
No response
Python version
No response
Jupyter version
No response
Installation
None
Reacted by George Woskob
Activity
jklymak commentedon Mar 21, 2025
We don;'t provide the styles
scienceorsiunitx. Without those files it is hard to know if this is a Matplotlib bug or a bug in wherever you got those style files. Can you make a reproducible, self contained example that just uses Matplotlib and numpy?anntzer commentedon Mar 22, 2025
I am almost certain that this is the same issue as the glyph sizing issue reported in #12928 (which that PR didn't fix). Probably need to revive #14159...
Repro:
anntzer commentedon Mar 22, 2025
Figured this out (after 6 years...). The following patch fixes the issue (it is derived from #27654 (comment) but not loading the incompatible type1cm anymore, which may have been the cause of the test failures reported in the linked comment)
It also supersedes #14159 which turns out to not have been the right approach after all. This would also close #27654 and #28675.
The fundamental underlying issue is the following: for glyph to path conversion (used by svg), textpath renders the text at fontsize FONT_SCALE = 100, and scales it appropriately after. But type1ec, despite its name, doesn't actually allow rendering glyphs such as the micro-sign or the won sign at that size; manually compiling the tex file generated by texmanager.py shows the warning
i.e. the micro sign is actually rendered ~3x smaller than the rest of the text (and then the ratio is kept when scaling down the text). Why greater sizes are now allowed remains a bit a mystery to me, as there's clearly an entry for bigger sizes in https://mirrors.ircam.fr/pub/CTAN/fonts/ps-type1/cm-super/type1ec.sty (
<35.83->#53583%) but heh. In any case, using fix-cm allows rendering these glyphs correctly at size 100 and fixes the issue.More links:
A side question that remains is whether textpath should really generate the glyphs at fontsize 100 and scale them (usually down) later. Indeed, size 100 computer modern is not the same as size 5 computer modern scaled up 20 times (see e.g. https://tex.stackexchange.com/questions/18721/). FWIW I don't see why textpath couldn't just do the rendering at the "real" requested size indicated in fontproperties...