Bug report

Bug summary

When I am using many scatter plot in a single 3D plot, the depth shade is not working.

Code for reproduction

from mpl_toolkits.mplot3d import Axes3D  t
import matplotlib.pyplot as plt
import numpy as np
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
xs = np.random.randn(100)
for i in range(100):
    ax.scatter(xs[i], ys[i], zs[i])
plt.show()

Actual outcome

Expected outcome
The point should have alpha levels in relation to the depth.
Matplotlib version

• Operating system: GoogleCloud
• Matplotlib version: 3.3.1
• Matplotlib backend:module://ipykernel.pylab.backend_inline
• Python version: 3.6
• Jupyter version (if applicable):
• Other libraries:

You can test it in this colab:
https://colab.research.google.com/drive/1XQv3aK44-_lebbgfWDYv-0genBe4QKR1