[Bug]: Font difference in Ubuntu for latest matplotlib

[ianhi]

Bug summary

The latest matplotlib has slightly different font positioning on Ubuntu than the released 3.7

This was discovered by ipympls tests here: matplotlib/ipympl#514 (comment)

Code for reproduction

import matplotlib.pyplot as plt
from matplotlib import __version__
import numpy as np

x = np.linspace(0,100,1000)
y = np.sin(x)


fig, ax = plt.subplots()
ax.plot(x,y)
plt.savefig(f"{__version__}.png")

Actual outcome

Run first with 3.7.0

and then with nightly wheel
(pip install --upgrade --pre --index-url https://pypi.anaconda.org/scipy-wheels-nightly/simple --extra-index-url https://pypi.org/simple matplotlib

This gives two images where the labels of the positive y-ticks are shifted slightly. Here's me toggling between the two generated images:

And here is the diff image from the ipympl tests

Expected outcome

No differences

Additional information

We also run latest tests on macos, and those did not fail, so this seems to be specific to ubuntu.

Operating system

Ubuntu

Matplotlib Version

latest

Matplotlib Backend

No response

Python version

No response

Jupyter version

No response

Installation

None

[ianhi]

quick bump of this - I'm pretty sure this should be considered a bug but would love to hear from someone else

[jklymak]

Are you locking your freetype between the two tests? We have a lot of image tests like this that would have broken if this were a change in Matplotlib.

[tacaswell]

If installing from the wheels we should have pinned freetype.

[QuLogic]

AFAICT, ipympl tests install matplotlib from conda-forge. This is built against conda-forge's FreeType and thus text rendering is dependent on which one conda-forge has.

If you want a fixed version, then you need to install our wheels, or install from the conda-forge/label/testing label, like we do in Cartopy https://github.com/SciTools/cartopy/blob/main/environment.yml#L18