Bug summary

Create e.g. a pathcollection (a scatter plot) not mapping any array, but with directly set colors; then update one of the facecolors before the first draw of the collection. This change has no effect and gets cancelled.

Code for reproduction

import matplotlib.pyplot as plt

sc1 = plt.scatter([0, 1, 2], [0, 1, 2], c=["r", "g", "b"])
sc2 = plt.scatter([0, 1, 2], [2, 3, 4], c=["r", "g", "b"])
# Update sc1 before the first draw.
sc1.get_facecolors()[2] = (0, 0, 0, 1)  # i.e. black.
plt.gcf().canvas.draw()
# Update sc2 after the first draw.
sc2.get_facecolors()[2] = (0, 0, 0, 1)  # i.e. black

plt.show()

Actual outcome

Note that the third point of sc1 is incorrectly blue, whereas the third point of sc2 is correctly black.

Expected outcome

Both third points are black.

Additional information

First noted by @chahak13 in #24474 (comment).
I haven't done a full bisect but did check that this broke at some point between 3.3.4 and 3.4.0, and I suspect #18480 introduced the issue (in the changes related to update_scalarmappable); attn @efiring.

Operating system

fedora37

Matplotlib Version

3.7.0.dev538+g9b4985e185

Matplotlib Backend

qtagg

Python version

3.10

Jupyter version

ENOSUCHLIB

Installation

git checkout