MNT: only account for Artists once in fig.get_tightbbox

[rcomer]

PR summary

Figure.get_tightbbox takes the union of the tightbbox's of all the artists attached to it. This includes each axes, whose tight_bbox incorporates all of their artists:

matplotlib/lib/matplotlib/axes/_base.py

Lines 4442 to 4452 in ff552f4

	if bbox_artists is None:
	bbox_artists = self.get_default_bbox_extra_artists()
	for a in bbox_artists:
	bbox = a.get_tightbbox(renderer)
	if (bbox is not None
	and 0 < bbox.width < np.inf
	and 0 < bbox.height < np.inf):
	bb.append(bbox)
	return mtransforms.Bbox.union(
	[b for b in bb if b.width != 0 or b.height != 0])

So it seems redundant to me to also add in the axes' artists individually. Removing these lines did not break any tests for me locally.

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines

[jklymak]

Could this get a small test since this method is public anyways. I also wonder if this needs an API change note just in case people were somehow using this to get all artists on a figure?

[rcomer]

Actually we can also leave the axes out from the list of artists as they are accounted for further down the Figure.get_tightbbox method:

matplotlib/lib/matplotlib/figure.py

Lines 1722 to 1731 in ff552f4

	for ax in self.axes:
	if ax.get_visible():
	# some axes don't take the bbox_extra_artists kwarg so we
	# need this conditional....
	try:
	bbox = ax.get_tightbbox(
	renderer, bbox_extra_artists=bbox_extra_artists)
	except TypeError:
	bbox = ax.get_tightbbox(renderer)
	bb.append(bbox)

@jklymak yep, I was wondering about the api change. Since the method is now just one list comprehension, we could put that list comprehension directly in get_tightbbox and deprecate get_default_bbox_extra_artists?

[jklymak]

I don't know if anyone really uses it this, but you could imagine passing a list of extra artists to get_tightbbox that is made from the list returned by get_default_bbox_extra_artists. Indeed maybe this is a reason to unpack the artists in the axes? Otherwise it's hard to add/remove artists from the list if they are down in the axes.

The set_in_layout property obviates the need for messing with these lists, and I think is a better solution to excluding artists - I don't know what would happen if we just got rid of them.

[rcomer]

I believe I have evidence of a measurable performance gain here #26150 (comment).

[jklymak]

I think we should maybe leave the public method alone because it is a way to get a flat list of all artists you may want to query on a Figure. It could be better named for a more general purpose, but you could imagine folks are using it

However, internally, we should probably stop using this method in favour of a hierarchy, as proposed here.

[rcomer]

OK, I've removed the deprecation. What happens to the helper method clearly no longer affects the purpose of this PR. If someone has an opinion what to do with it (rename, deprecate,...) it could always be done separately.

[jklymak]

Still makes sense to me.