Warn re: Axes3D constructor behavior change in mpl3.4 #18939
Description
According to git bisect, 261f706 by @anntzer broke the following code, adapted from the examples -- it produces a blank / empty plot:
from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt
import numpy as np
fig = plt.figure()
ax = Axes3D(fig)
# ax = fig.gca(projection='3d')
X = np.arange(-5, 5, 0.25)
Y = np.arange(-5, 5, 0.25)
X, Y = np.meshgrid(X, Y)
R = np.sqrt(X**2 + Y**2)
Z = np.sin(R)
surf = ax.plot_surface(X, Y, Z)
If you comment out the ax = Axes3D(fig) line and use ax = fig.gca(projection='3d'), it works fine. It also works fine on the preceding commit 34f99a9.