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GeezerVison is showing github.com — Update pgf baseline image for TeX Live 2025 by axel-j-larsson · Pull Request #32504 · matplotlib/matplotlib

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axel-j-larsson commented Oct 19, 2026

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PR summary

Fixes issue #29790. Also relates to PR #32478 .
With TeX Live 2025, test_backend_pgf.py was failing due to pgf_rcupdate2, where a single character had changed location by a pixel:

I investigated it and the PGF files generated by pgf_backend.py were identical between TeX Live versions. After manually regenerating the PDFs from the same PGF file with both TeX Live 2025 and 2024, I found that their contents differed slightly in regards to object positioning. After additionally manually rasterizing the output with ghostscript (as done in the test), the same one-pixel difference appeared in both the files created by Matplotlib and the ones generated and rasterized manually.

It appears that the difference is instead caused by updates in PDFTeX's rendering engine, and would as such not be anything directly caused by a bug in Matplotlib. As such, I determined the most suitable fix would be to update the baseline image. I have also checked the new baseline with TeX Live 2026, and it still passes there.

However, the new baseline does instead fail for TeX Live 2024 (and presumably earlier versions as well). As such, the suitability of this PR depends on what which TeX Live version to support, and in extension which Ubuntu version to support (see #32478).

AI Disclosure

AI was used to help investigate the image difference and generate new PDFs directly with pdfLaTeX. However, the new baseline test results have been verified and reviewed manually.

PR quality check

Use an expressive title, e.g. "Fix title font property precedence"
New and changed code is tested
N/A Plotting related features are demonstrated in an example
N/A New features and API changes have release notes
N/A Documentation complies with general and docstring guidelines

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github-actions Bot commented Oct 19, 2026

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github-actions Bot added the first-contribution label

Oct 19, 2026

axel-j-larsson mentioned this pull request

Oct 19, 2026

[Bug]: pgf_rcupdate1 in test_backend_pgf.py::test_rcupdate fails for TeX Live 2026 #32505

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iccir added the backend: pgf label

Oct 19, 2026

axel-j-larsson commented Oct 27, 2026

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Hi @iccir, just checking back to see if there were any plans on changing the CI to use TeX Live 2025. If not, would it perhaps be a good idea to instead specify which version of it that is expected in the docs?

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iccir commented Oct 27, 2026

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I'm honestly not sure, as this isn't my area of expertise. My instinct would be to pick the TeX Live version with the most users and then xfail the tests on other configurations. Ultimately, all tests either need to pass or be expected to fail.

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          Make pgf_rcupdate2 xfail for newer pdftex versions

180b65c

axel-j-larsson force-pushed the fix-pgf-test-baseline-image branch from 1359e47 to 180b65c Compare

November 4, 2026 17:51

github-actions Bot removed the backend: pgf label

Nov 4, 2026

iccir reviewed

Nov 4, 2026

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lib/matplotlib/tests/test_backend_pgf.py Outdated

		'\\usepackage{sfmath}')}]
		tol = [0, 13.2] if _old_gs_version else [0, 0]
		for i, rc_set in enumerate(rc_sets):
		if i == 1 and mpl._get_executable_info('pdflatex').version > Version('1.40.26'):

iccir Nov 4, 2026

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I think this should be parse_version to match existing code.

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iccir Nov 4, 2026

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Additionally, can mpl._get_executable_info('pdflatex') return None for info?

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axel-j-larsson Nov 4, 2026

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As far as I can tell, pdflatex has used the same versioning format since mid 2005, so as long as a version that isn't older than that is used it shouldn't return None.

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lib/matplotlib/__init__.py Outdated

		f"version supported by Matplotlib is 3.0")
		return info
		elif name == "pdflatex":
		return impl(["pdflatex", "-v"], r"pdfTeX .*-(\d+\.\d+\.\d+)")

iccir Nov 4, 2026

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Is there any danger of -v failing on old pdflatex? See other review comment about returning None.

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axel-j-larsson Nov 4, 2026

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Using -version instead might be better, as I believe it has been supported for longer.

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          Update -version option & use parse_version

dd0ed5b

axel-j-larsson requested a review from iccir

November 5, 2026 21:43

axel-j-larsson commented Nov 5, 2026

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I did some revisions based on your feedback. Although the codecov check is failing (and for some reason I cannot access the line-by-line analysis of it either) and I am unsure whether something needs to be done in regards to that (and if so what).

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axel-j-larsson commented Nov 11, 2026

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Hi again @iccir, just checking back in case you missed my previous update. Thanks

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iccir reviewed

Nov 11, 2026

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lib/matplotlib/tests/test_backend_pgf.py

		for i, rc_set in enumerate(rc_sets):
		if (i == 1 and
		mpl._get_executable_info('pdflatex').version > parse_version('1.40.26')):
		pytest.xfail(reason="This test currently requires a pdfTeX "

iccir Nov 11, 2026

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Checking i == 1 seems fragile. Could we check the value of pgf.texsystem instead?

I'm a bit confused, however - why are we checking for 1.40.26 or earlier and not requiring a newer version of TeX Live? If TeX Live 2025 is more widely used, I think that we should have tests / images that pass on it and then xfail on older versions.

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