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[Bug]: Legend overlaps shaded area in fill_between with legend location "best" #27414
Description
Bug summary
When using the fill_between function in matplotlib with a legend and specifying the legend location as "best", the legend is not taking into account the shaded area and may overlap with it.
Code for reproduction
import matplotlib.pyplot as plt
import numpy as np
# Example data
x = np.linspace(0, 5, 100)
y1 = 0.5 * np.exp(x) - 1
y2 = 2 * np.exp(x) + 1
# Plotting shaded area
plt.fill_between(x, y1, y2, color='gray', alpha=0.5, label='Shaded Area')
# Set y-axis limit
plt.ylim(-10, 100)
# Adding legend with location "best"
plt.legend(loc='best')
# Show the plot
plt.show()Actual outcome
Expected outcome
Additional information
No response
Operating system
Windows 11
Matplotlib Version
3.8.0
Matplotlib Backend
module://backend_interagg
Python version
Python 3.11.5
Jupyter version
No response
Installation
conda
Activity
AaronCodesPython commented on Dec 1, 2023
I would like to take on this issue
AaronCodesPython commented on Dec 2, 2023
The problem seems to be in the _auto_legend_data function in legend.py. fill_between does not add anything that is considered in the calculation of "badness"
badness = (sum(legendBox.count_contains(line.vertices) for line in lines) + legendBox.count_contains(offsets) + legendBox.count_overlaps(bboxes) + sum(line.intersects_bbox(legendBox, filled=False) for line in lines))
I will try to resolve this until next Saturday.
oscargus commented on Dec 4, 2023
FWIW, if you dig into this, there is also #23323 which appears to have a similar root cause. (Solving one of them is clearly enough to get a PR accepted, but it may be that one can quite easily solve both in one go.)
ksunden commented on Dec 4, 2023
Okay, so the result of fill_between is a PolyCollection object. this is technically included in the badness calculation, but only kind of... as what it is actually including is the offset of each element in the PolyCollection. This is the case because a (path)collection is returned by scatter, where the offsets are the center points that should be considered (and also for other kinds of collections, like pcolor, etc)
Perhaps it could be treated as patch and line are? (Though wonder a bit about the performance impact especially for e.g. scatter, this is already a bit of a bottleneck that carries a warning if it takes too long.