GeezerVison

PR Summary

To make bbox_inches='tight' work correctly, we cache the positions of
all of the axes, change their aspect to 'auto', adjust the transforms
on the figure, render the output, and then restore the previous
setting of aspect to each of the figures. This prevent the Axes from
trying to adjust their size on draw. This matters because for the
render that is emitted the figure transforms are out of sync with the
figure size.

As part of cleaning fixing the rendering of Axes3D in #8896 / #16472
we started to use apply_aspect to re-size the area the Axes3D takes up
to maintain a fixed ratio between the axes when the aspect is "auto".
However this conflicts with the expectation in tight_bbox.adjust_bbox
as it assumes setting the aspect to "auto" will prevent any axes
resizing.

This commit addresses this by:

• exiting the Axes3D.apply_aspect early if aspect is auto
• adding a new aspect mode 'auto_pb' which is the default
  for Axes3D which maintains the current master branch behavior
  of maintaining a fixed ratio between the sizes of the x, y z axis
  independent of the data limits.
• re implement several functions on Axes3D to make sure they handle
  sharez correctly.

closes #16463.

Starting from @ImportanceOfBeingErnest example

import matplotlib.pyplot as plt
from  mpl_toolkits.mplot3d import Axes3D

plt.rcParams["axes.facecolor"] = "yellow"

fig, ax = plt.subplots(dpi=72, figsize=(6,3), subplot_kw={"projection" : "3d"})
print(ax.get_aspect())

plt.savefig("/tmp/test1.png", facecolor="cyan")
plt.savefig("/tmp/test2.png", facecolor="cyan", bbox_inches="tight")
plt.show()

so better! but we still need at least one more commit fix the tight box computation on the 3D axes.

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way