LineCollection.contains does not include caps around vertices, unlike Line2D.contains

[anntzer]

Bug report

Bug summary

Line2D.contains returns True for clicks just "beyond" the vertices of the Line2D, as long as they're not more than pickradius away from the vertex. On the contrary, LineCollection returns False for any click that's beyond the vertices.
In particular, this can make it difficult to click on "short" LineCollections.

Code for reproduction

from matplotlib import pyplot as plt
from matplotlib.backend_bases import MouseEvent
import numpy as np

fig, axs = plt.subplots(2)
line, = axs[0].plot([-1, 1], [0, 0])
coll = axs[1].hlines(0, -1, 1)

fig.canvas.draw()

for ax, art in zip(axs, [line, coll]):
    ax.set(xlim=(-2, 2), ylim=(-.5, .5))
    art.set_pickradius(20)
    for x in np.linspace(*ax.get_xlim())[1:-1]:
        for y in np.linspace(*ax.get_ylim())[1:-1]:
            x1, y1 = ax.transData.transform((x, y))
            contained, _ = art.contains(
                MouseEvent("button_press_event", fig.canvas, x1, y1))
            ax.plot(x, y, "o", c="g" if contained else "r", ms=1)

plt.show()

Actual outcome

Green points are considered as "contained".

Expected outcome

Same green points above and below, with round "caps" at the ends.

Matplotlib version

• Operating system: linux
• Matplotlib version: master, likely since a very long time
• Matplotlib backend (print(matplotlib.get_backend())): any
• Python version: 38
• Jupyter version (if applicable): no
• Other libraries: no

[github-actions]

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