PR Summary

Opening this as a draft for discussion.

If someone passes in a 2-D array to.pcolormesh() should we automatically call.ravel() on it? See question from@jklymak here:#24619 (comment) Flattening is what historically has been done, but we've been moving towards QuadMesh being a primary 2-D collection lately and could get rid of this restriction on flattening input.

The updates here are all primarily surrounding what shapes the returned arrays are from the function calls and how to compare them, so drawing hasn't changed. Also note that this would introduce a deviation betweenpcolor(z2d).get_facecolors() == colors1d which returns the flattened array, whilepcolormesh(z2d).get_facecolors() == colors2d returns the original shape of the array passed in.

Collection classes have a lot of "1D list of objects" method handling in them, but inQuadMesh there is additional handling for the known 2-D structure of the arrays (mesh in the name).pcolor() returns aPolyCollection which is a 1D list of Polygons, and if there are masked elements it will actually shrink the list and not add that Polygon, so it would require more book-keeping (maybe adding a newPolyMeshCollection just for pcolor) to get the 2-D logic right.

PR Checklist

Documentation and Tests

• Has pytest style unit tests (andpytest passes)
• Documentation is sphinx and numpydoc compliant (the docs shouldbuild without error).
• New plotting related features are documented with examples.

Release Notes

• New features are marked with a.. versionadded:: directive in the docstring and documented indoc/users/next_whats_new/
• API changes are marked with a.. versionchanged:: directive in the docstring and documented indoc/api/next_api_changes/
• Release notes conform with instructions innext_whats_new/README.rst ornext_api_changes/README.rst