8000 [Bug]: PGF font size mismatch between measurement and output · Issue #26892 · matplotlib/matplotlib · GitHub
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[Bug]: PGF font size mismatch between measurement and output #26892

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Socob opened this issue Sep 23, 2023 · 1 comment · Fixed by #26893
Closed

[Bug]: PGF font size mismatch between measurement and output #26892

Socob opened this issue Sep 23, 2023 · 1 comment · Fixed by #26893
Milestone
v3.10.0

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@Socob
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Socob commented Sep 23, 2023 •
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Bug summary

When using the PGF backend, different LaTeX document font size settings are used when measuring widths vs. producing output. Although this is usually not a problem (since all text produced by the PGF backend locally sets the font properties), packages used in the custom preamble (such as unicode-math) may depend on the font size settings, leading to incorrect width measurements since different outcomes are produced in the two cases.

Code for reproduction

import matplotlib
import matplotlib.pyplot as plt

matplotlib.use('pgf')

plt.rc('text', usetex=True)  # not sure if this is actually relevant for PGF backend?
plt.rc('pgf', texsystem='lualatex', rcfonts=False, preamble=r'''
    \usepackage{unicode-math}
''')

plt.figure()
plt.plot([], label=r'$this is a very very very long math label a \times b + 10^{-3}$ and some text')
plt.legend()
plt.savefig('test_math.png')
plt.savefig('test_math.pgf')

Actual outcome

Math text has a different width (characters are comparatively wider when scaled to the same height) and thus exceeds the legend boundary (tick labels also have some slight spacing issues):

MWE output showing the problem

Expected outcome

Text should be within the legend boundary:

Fixed MWE output

Additional information

The main issue causing the problem in my example is that different font sizes are passed to \documentclass in different cases:

matplotlib/lib/matplotlib/backends/backend_pgf.py

Lines 186 to 188 in ff552f4

def _build_latex_header():
latex_header = [
r"\documentclass{article}",

matplotlib/lib/matplotlib/backends/backend_pgf.py

Line 813 in ff552f4

r"\documentclass[12pt]{article}",

matplotlib/lib/matplotlib/backends/backend_pgf.py

Line 923 in ff552f4

r"\documentclass[12pt]{article}",

This specific issue is only present in matplotlib ≥ v3.6.0 and seems to be a historical accident carried over from when the document class was changed from minimal to article in 4d85f70 (#23443). \documentclass{minimal} actually ignores any options passed to it (including 12pt), so that option in the original code was spurious and there was no mismatch between the cases with and without this option. But when this was changed to \documentclass{article}, the option 12pt did start taking effect, leading to the discrepancy.

However, more generally, the code always had an implicit dependence on the LaTeX font size setting, which does affect things like the unicode-math package (which selects different versions of math fonts depending on the font size). So when saving as .pgf and using these files directly in LaTeX documents, there is still the potential for problems to show up. Another consequence of this is that the standard LaTeX font size commands (\tiny, …, \normalsize, …, \Huge) are also relative to this obscure font size setting (instead of rcParams['font.size']).

Workaround for current releases: Manually set the font size in the preamble.

import matplotlib
import matplotlib.pyplot as plt

matplotlib.use('pgf')

plt.rc('text', usetex=True)  # not sure if this is actually relevant for PGF backend?
plt.rc('pgf', texsystem='lualatex', rcfonts=False, preamble=r'''
    \usepackage[fontsize=10pt]{scrextend}
    \usepackage{unicode-math}
''')

plt.figure()
plt.plot([], label=r'$this is a very very very long math label a \times b + 10^{-3}$ and some text')
plt.legend()
plt.savefig('test_math.png')
plt.savefig('test_math.pgf')

Operating system

No response

Matplotlib Version

3.8.0

Matplotlib Backend

pgf

Python version

No response

Jupyter version

No response

Installation

pip
@Socob Socob mentioned this issue Sep 23, 2023
Merged
2 tasks
Socob pushed a commit to Socob/matplotlib that referenced this issue Oct 3, 2023
Add image test for matplotlib#26892
b9301dc
Socob added a commit to Socob/matplotlib that referenced this issue Oct 3, 2023
@Socob
Add image test for matplotlib#26892
54b4eda
Socob added a commit to Socob/matplotlib that referenced this issue Oct 3, 2023
@Socob
Add image test for matplotlib#26892
3a4a86e
Socob added a commit to Socob/matplotlib that referenced this issue Oct 3, 2023
@Socob
Add image test for matplotlib#26892
ab50f7e
Socob added a commit to Socob/matplotlib that referenced this issue Oct 3, 2023
@Socob
Add image test for matplotlib#26892
4736de1
@ainar
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ainar commented Nov 6, 2023

Thank you for the workaround. I had a related problem:
The width of the text objects was miscalculated, so it led to too much space between my axis and my rotated tick labels.

What constantly happens because of that is also that the legend boxes were systematically too big compared to the inner text. Usually, that is not a problem, but when the text is too long, this is more of an issue.

This was referenced Apr 22, 2024
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Socob added a commit to Socob/matplotlib that referenced this issue Apr 22, 2024
@Socob
Add image test for matplotlib#26892
5d0852f
Socob added a commit to Socob/matplotlib that referenced this issue Apr 22, 2024
@Socob
Add image test for matplotlib#26892
4a4a41f
@QuLogic QuLogic added this to the v3.10.0 milestone May 7, 2024
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PGF: Consistently set LaTeX document font size Socob/matplotlib
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