feature request: python version dependent reference images

[rsokolewicz]

hi! I have a project with a CI/CD pipeline that runs pytest across different python versions, and today ran into a rather annoying issue where the matplotlib images on py3.10 are slightly different from py3.13 (text being offset by a few pixels). Now, if I regenerate the reference images on 3.10, the tests on 3.13 will fail, and the other way around as well.

I was hoping to be able to add python-version dependent reference images. Something like

@pytest.mark.mpl_image_compare(baseline_dir="baselines/{py_version}")
def test_my_plot():
...

which would detect the python version. Then the user (me) could run

pytest --mpl-generate-path=baselines/3.10

and

pytest --mpl-generate-path=baselines/3.13

if i need version dependent reference images.

edit: matplotlib 3.11 introduced a new text renderer that causes the mismatching images. The release notes https://matplotlib.org/stable/release/prev_whats_new/whats_new_3.11.0.html#fonts-and-text highlight a few workarounds. Adding here in case someone stumbles on this issue.

[rcomer]

Over in Cartopy we have a hook that, among other things, sets a default baseline_dir. I guess that could be adapted to be python version dependent.
https://github.com/SciTools/cartopy/blob/e2b775d7568e786c649c9dd1ef9f19bb62716dbc/lib/cartopy/tests/mpl/conftest.py#L25-L40

[rsokolewicz]

Over in Cartopy we have a hook that, among other things, sets a default baseline_dir. I guess that could be adapted to be python version dependent. https://github.com/SciTools/cartopy/blob/e2b775d7568e786c649c9dd1ef9f19bb62716dbc/lib/cartopy/tests/mpl/conftest.py#L25-L40

oh, yes. I could give that a try as well.