Tweak callbacks to generate pick events.

Currently, pick events are generated by button_press and scroll events,
which call canvas.pick, which itself checks the widgetlock and then
calls Figure.pick, which is actually Artist.pick; Artist.pick checks
whether to emit a PickEvent for the current artist, then calls itself
recursively on children artists.

This PR gets rid of the intermediate canvas.pick layer, moving the
widgetlock check to Figure.pick (Figure.pick still calls the super()
pick, i.e. Artist.pick, after the check).  The advantages are that 1)
this avoids colliding with pick methods that may be present in the
native GUI classes (this is not a theoretical case: see the changes in
the GTK4 case) and 2) this makes it easier to fix button_pick_id and
scroll_pick_id to use picklable connections (which they should do).  In
the old implementation, lambdas were not picklable, and one could not
write e.g. `mpl_connect("button_press_event", self.canvas.pick)` because
that would not handle canvas swapping.

Author: anntzer

doc/api/next_api_changes/deprecations/23448-AL.rst

@@ -0,0 +1,4 @@
+``FigureCanvasBase.pick``
+~~~~~~~~~~~~~~~~~~~~~~~~~
+... is deprecated.  Directly call `.Figure.pick`, which has taken over the
+responsibility of checking the canvas widgetlock as well.

lib/matplotlib/backend_bases.py

@@ -1697,6 +1697,7 @@ def is_saving(self):
         """
         return self._is_saving
 
+    @_api.deprecated("3.6", alternative="canvas.figure.pick")
     def pick(self, mouseevent):
         if not self.widgetlock.locked():
             self.figure.pick(mouseevent)

lib/matplotlib/backends/backend_gtk4.py

@@ -79,11 +79,6 @@ def __init__(self, figure=None):
         style_ctx.add_provider(css, Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION)
         style_ctx.add_class("matplotlib-canvas")
 
-    def pick(self, mouseevent):
-        # GtkWidget defines pick in GTK4, so we need to override here to work
-        # with the base implementation we want.
-        FigureCanvasBase.pick(self, mouseevent)
-
     def destroy(self):
         self.close_event()
 

lib/matplotlib/figure.py

@@ -2372,10 +2372,10 @@ def __init__(self,
         # pickling.
         self._canvas_callbacks = cbook.CallbackRegistry(
             signals=FigureCanvasBase.events)
-        self._button_pick_id = self._canvas_callbacks.connect(
-            'button_press_event', lambda event: self.canvas.pick(event))
-        self._scroll_pick_id = self._canvas_callbacks.connect(
-            'scroll_event', lambda event: self.canvas.pick(event))
+        self._button_pick_id = self._canvas_callbacks._connect_picklable(
+            'button_press_event', self.pick)
+        self._scroll_pick_id = self._canvas_callbacks._connect_picklable(
+            'scroll_event', self.pick)
 
         if figsize is None:
             figsize = mpl.rcParams['figure.figsize']
@@ -2423,6 +2423,10 @@ def __init__(self,
         # list of child gridspecs for this figure
         self._gridspecs = []
 
+    def pick(self, mouseevent):
+        if not self.canvas.widgetlock.locked():
+            super().pick(mouseevent)
+
     def _check_layout_engines_compat(self, old, new):
         """
         Helper for set_layout engine