Regenerate background when RectangleSelector active-flag is set back on.

anntzer · anntzer · commit 80cb23712201 · 2020-05-22T00:18:44.000+02:00
Otherwise, if the selector is made inactive and then back to active, the
"old" selector gets captured in the background image and spurious
appears.

No tests because good luck with that, but can be tried with
examples/widgets/rectangle_selector.py.
diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
@@ -2057,6 +2057,23 @@ def __init__(self, ax, onselect, drawtype='box',
 
         self._extents_on_press = None
 
+    def update_background(self, event):
+        if not self.useblit:
+            return
+        # Make sure that widget artists don't get accidentally included in the
+        # background, by re-rendering the background if needed (and then
+        # re-re-rendering the canvas with the visible widget artists).
+        needs_redraw = any(artist.get_visible() for artist in self.artists)
+        with ExitStack() as stack:
+            if needs_redraw:
+                for artist in self.artists:
+                    stack.callback(artist.set_visible, artist.get_visible())
+                    artist.set_visible(False)
+                self.canvas.draw()
+            super().update_background(event)
+        if needs_redraw:
+            self.update()
+
     def _press(self, event):
         """on button press event"""
         # make the drawn box/line visible get the click-coordinates,
