plot_surface with facecolors distorts colors due to default shading=True #30290
Description
Summary
import numpy as np
import matplotlib.pyplot as plt
from matplotlib import cm
from matplotlib.colors import Normalize
X = np.linspace(0, 1, 100)
Y = np.linspace(0, 1, 100)
X_mesh, Y_mesh = np.meshgrid(X, Y)
Z = np.cos((1-X_mesh) * np.pi)*np.cos((1-Y_mesh) * np.pi)*1e+14 + 1.4e+15
Z_colors = np.cos(X_mesh * np.pi)
norm = Normalize(vmin=np.min(Z_colors), vmax=np.max(Z_colors))
colors = cm.gist_heat_r(norm(Z_colors))[:-1, :-1]
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
ax.plot_surface(X_mesh, Y_mesh, Z, facecolors=colors, edgecolor='none')
plt.show()Proposed fix
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
ax.plot_surface(X_mesh, Y_mesh, Z, facecolors=colors, edgecolor='none', shade=False)
plt.show()When colors represent actual data values, shading-induced distortion is critical.
- If
facecolorsis explicitly given,shade=Falseshould be the default behavior, since the user is already controlling the color manually. - Alternatively, at minimum, this behavior should be clearly documented in the
plot_surfaceAPI page, warning users that shading will distort manually specified facecolors. - Or, provide an explicit warning if both
facecolorsandshade=Trueare used together.