It seems like all the cases you've changed had the size available, and theset_context calls are only there, so why do we need to go to the trouble to infer the size instead of passing it in as another argument?

Mostly, this was motivated by the hidpi changes in gtk3/4agg, where having to fiddle with the dpi scale seems a bit inelegant, when the info is in fact already carried by the context.
It also seems strange to have two APIs (set_ctx_from_surface/set_context and set_width_height) where calls to the first always must be followed by a call to the second, and the args to the second call are in addition completely determined by the first.

Milestoning as 3.6, as this modifies the semantics of an API introduced in#21981 for 3.6.

@oscargus is there a reason you approved but did not merge? Our policy is that PRs need two positive reviews. With giving you review permissions we also trust you to push the merge button if the two approvals are there.

I may not recall exactly, but I believe that it wasn't clear to me if the query from@QuLogic was settled or not. With the assumption that two approvals may not override a concern.

I believe that it wasn't clear to me if the query from@QuLogic was settled or not. With the assumption that two approvals may not override a concern.

That's a valid point. In that case I suggest to explicitly mention the open issue, so that it's clear what is still missing for the merge, e.g.

LGTM.@QuLogic is your question reasonably addressed by@anntzer's comment?

or

Approved modulo@QuLogic's comment.

In that case I suggest to explicitly mention the open issue

Fair enough.

I try that now then:@QuLogic are you OK with merging?

(Reading the code again, it may make sense to factor out a method,_get_context_size or something similar, for readability, but not required.)

Marking as RC as this modifies a new API for mpl3.6 (so it's better to do this with no intervening deprecation), and there's at least one user that would benefit from this athttps://discourse.matplotlib.org/t/draw-plot-into-existing-cairo-context/22687.
@QuLogic Any thoughts here?

ping@QuLogic again - this is waiting for your OK....