[ENH]: nested volumes with one ax.voxels call using alpha #26106
Description
Problem
Trying to plot a volume inside a volume, with one ax.voxels call, doesn't seem possible:
import matplotlib.pyplot as plt
import numpy as np
from matplotlib import colors
inner = np.zeros((4, 4, 4), dtype=bool)
inner[1:3, 1:3, 1:3] = 1
outer = np.ones((4, 4, 4), dtype=bool)
voxelarray = inner | outer
facecolors = np.empty(voxelarray.shape + (4,), dtype=object)
facecolors[outer] = colors.to_rgba("blue", alpha=0.5)
facecolors[inner] = colors.to_rgba("red")
fig = plt.figure()
ax = fig.add_subplot(projection="3d")
ax.voxels(voxelarray, facecolors=facecolors)
fig.savefig("nested_volumes.png")
Nest volumes are possible if invoking ax.voxels twice:
outer_facecolors = np.empty(outer.shape + (4,), dtype=object)
outer_facecolors[outer] = colors.to_rgba("blue", alpha=0.5)
inner_facecolors = np.empty(inner.shape, dtype=object)
inner_facecolors[inner] = "red"
fig = plt.figure()
ax = fig.add_subplot(projection="3d")
ax.voxels(outer, facecolors=outer_facecolors)
ax.voxels(inner, facecolors=inner_facecolors)
ax.set_axis_off()
plt.tight_layout()
fig.savefig("nested_volumes.png", transparent=True)
Proposed solution
It would be nice if matplotlib supported alpha with voxels for nested volumes.
Related: https://stackoverflow.com/questions/48672663/matplotlib-render-all-internal-voxels-with-alpha, which leads to the dupe #9745 that was closed due to inactivity