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[Bug]: Surface draws incorrectly after set_verts on Poly3DCollection  #21163

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@ccaprani

Description

@ccaprani

Bug summary

Surface is not rendered properly after changing the data using set_verts: the simple MWE below shows the effect.

Code for reproduction

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

x = np.array([10, -10])
y = np.array([25, -25])
z = 5

X, Y = np.meshgrid(x, y)
Z = z * np.ones_like(X)

fig = plt.figure(figsize=(8, 4.5))
ax = fig.add_subplot(projection="3d")

ax.axes.set_xlim3d(left=-15, right=15)
ax.axes.set_ylim3d(bottom=-30, top=30)
ax.axes.set_zlim3d(bottom=0, top=10)

surf = ax.plot_surface(X, Y, Z, color="r", alpha=0.3)
plt.pause(1.0)

time = np.linspace(0, 5, 101)
for t in time:
    zt = z + 2 * np.sin(2 * np.pi * t)
    Z = zt * np.ones_like(X)
    verts = np.array([X, Y, Z]).T.reshape(4, 3)
    surf.set_verts(verts)
    plt.pause(0.1)

Actual outcome

image

Expected outcome

The full surface, as is shown prior to updating using set_verts should be shown:

image

Operating system

Ubuntu 21.04

Matplotlib Version

3.4.2

Matplotlib Backend

Qt5Agg

Python version

3.8.11

Jupyter version

No response

Other libraries

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Installation

conda

Conda channel

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