Bug summary

Contour labelling is hard, but our algorithm seems to create lots of overlaps when there is substantial room for non-overlaps.

Code for reproduction

import matplotlib.pyplot as plt
import numpy as np
import matplotlib as mpl

fig, ax = plt.subplots(1, 1, figsize=(2, 4))

x = np.linspace(1, 4, 20)
y = np.linspace(1, 4, 20)
X, Y = np.meshgrid(x, y)
cnt = ax.contour(X, Y, X, levels=20)
ax.clabel(cnt, levels=cnt.levels)
plt.show()

Actual outcome

Expected outcome

The labels would be staggered vertically.

Additional information

I'm not aware if this ever worked optimally. There was some optimization of the algorithm in #19018, but checking out v3.3.4 doesn't change the result.

Operating system

No response

Matplotlib Version

master...

Matplotlib Backend

No response

Python version

No response

Jupyter version

No response

Installation

No response