Assign event to later Axes if zorders are tied.

anntzer · anntzer · commit 7a8a8e73eae8 · 2017-10-21T12:09:23.000-07:00
If axes zorders are tied, axes appearing later in figure.axes get
drawn above those appearing earlier, so events should be preferably
assigned to them.  By default, max() returns the *first* maximum in case
of ties, so the previous implementation was not satisfactory.
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -1527,22 +1527,19 @@ def __init__(self, name, canvas, x, y, guiEvent=None):
         else:
             axes_list = [self.canvas.mouse_grabber]
 
-        if axes_list:  # Use highest zorder.
-            self.inaxes = max(axes_list, key=lambda x: x.zorder)
-        else:  # None found.
-            self.inaxes = None
-            self._update_enter_leave()
-            return
-
-        try:
-            trans = self.inaxes.transData.inverted()
-            xdata, ydata = trans.transform_point((x, y))
-        except ValueError:
-            self.xdata = None
-            self.ydata = None
+        if axes_list:
+            self.inaxes = cbook._topmost_artist(axes_list)
+            try:
+                trans = self.inaxes.transData.inverted()
+                xdata, ydata = trans.transform_point((x, y))
+            except ValueError:
+                self.xdata = None
+                self.ydata = None
+            else:
+                self.xdata = xdata
+                self.ydata = ydata
         else:
-            self.xdata = xdata
-            self.ydata = ydata
+            self.inaxes = None
 
         self._update_enter_leave()
 
@@ -1805,7 +1802,7 @@ def onRemove(self, ev):
             canvas.mpl_connect('mouse_press_event',canvas.onRemove)
         """
         # Find the top artist under the cursor
-        under = sorted(self.figure.hitlist(ev), key=lambda x: x.zorder)
+        under = cbook._topmost_artist(self.figure.hitlist(ev))
         h = None
         if under:
             h = under[-1]
@@ -2893,7 +2890,7 @@ def mouse_move(self, event):
                            if a.contains(event) and a.get_visible()]
 
                 if artists:
-                    a = max(artists, key=lambda x: x.zorder)
+                    a = cbook._topmost_artist(artists)
                     if a is not event.inaxes.patch:
                         data = a.get_cursor_data(event)
                         if data is not None:
diff --git a/lib/matplotlib/backend_tools.py b/lib/matplotlib/backend_tools.py
@@ -340,7 +340,7 @@ def send_message(self, event):
                            if a.contains(event) and a.get_visible()]
 
                 if artists:
-                    a = max(artists, key=lambda x: x.zorder)
+                    a = cbook._topmost_artist(artists)
                     if a is not event.inaxes.patch:
                         data = a.get_cursor_data(event)
                         if data is not None:
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -21,6 +21,7 @@
 from itertools import repeat
 import locale
 import numbers
+import operator
 import os
 import re
 import sys
@@ -2752,3 +2753,16 @@ def _get_key_params(self):
                              (params, str_func))
 
         return str_func, params
+
+
+def _topmost_artist(
+        artists,
+        _cached_max=functools.partial(max, key=operator.attrgetter("zorder"))):
+    """Get the topmost artist of a list.
+
+    In case of a tie, return the *last* of the tied artists, as it will be
+    drawn on top of the others. `max` returns the first maximum in case of ties
+    (on Py2 this is undocumented but true), so we need to iterate over the list
+    in reverse order.
+    """
+    return _cached_max(reversed(artists))
