axes_grid1: add host/parasite axes pick methods

Fixes #5581
matplotlib · timhoffm · Feb 14, 2019 · Jan 4, 2019 · Feb 12, 2019 · c582fa18bf56621565a7af3f14d5d4d76bfe91b1
commit c582fa18bf56621565a7af3f14d5d4d76bfe91b1
diff --git a/lib/mpl_toolkits/axes_grid1/parasite_axes.py b/lib/mpl_toolkits/axes_grid1/parasite_axes.py
@@ -36,6 +36,18 @@ def cla(self):
             self.xaxis.set_zorder(2.5)
             self.yaxis.set_zorder(2.5)
 
+    def pick(self, mouseevent):
+        # This most likely goes to Artist.pick (depending on axes_class given
+        # to the factory), which only handles pick events registered on the
+        # axes associated with each child:
+        super().pick(mouseevent)
+        # But parasite axes are additionally given pick events from their host
+        # axes (cf. HostAxesBase.pick), which we handle here:
+        for a in self.get_children():
+            if (hasattr(mouseevent.inaxes, "parasites")
+                    and self in mouseevent.inaxes.parasites):
+                a.pick(mouseevent)
+
 
 @functools.lru_cache(None)
 def parasite_axes_class_factory(axes_class=None):
@@ -232,6 +244,13 @@ def cla(self):
             ax.cla()
         super().cla()
 
+    def pick(self, mouseevent):
+        super().pick(mouseevent)
+        # Also pass pick events on to parasite axes and, in turn, their
+        # children (cf. ParasiteAxesBase.pick)
+        for a in self.parasites:
+            a.pick(mouseevent)
+
     def twinx(self, axes_class=None):
         """
         create a twin of Axes for generating a plot with a sharex

diff --git a/lib/mpl_toolkits/tests/test_axes_grid1.py b/lib/mpl_toolkits/tests/test_axes_grid1.py
@@ -17,6 +17,7 @@
     AnchoredSizeBar,
     AnchoredDirectionArrows)
 
+from matplotlib.backend_bases import MouseEvent
 from matplotlib.colors import LogNorm
 from matplotlib.transforms import Bbox, TransformedBbox
 from itertools import product
@@ -422,3 +423,61 @@ def test_gettightbbox():
     bbox = fig.get_tightbbox(fig.canvas.get_renderer())
     np.testing.assert_array_almost_equal(bbox.extents,
                                          [-17.7, -13.9, 7.2, 5.4])
+
+
+@pytest.mark.parametrize("click_on", ["big", "small"])
+@pytest.mark.parametrize("big_on_axes,small_on_axes", [
+    ("gca", "gca"),
+    ("host", "host"),
+    ("host", "parasite"),
+    ("parasite", "host"),
+    ("parasite", "parasite")
+])
+def test_picking_callbacks_overlap(big_on_axes, small_on_axes, click_on):
+    """Test pick events on normal, host or parasite axes."""
+    # Two rectangles are drawn and "clicked on", a small one and a big one
+    # enclosing the small one. The axis on which they are drawn as well as the
+    # rectangle that is clicked on are varied.
+    # In each case we expect that both rectangles are picked if we click on the
+    # small one and only the big one is picked if we click on the big one.
+    # Also tests picking on normal axes ("gca") as a control.
+    big = plt.Rectangle((0.25, 0.25), 0.5, 0.5, picker=5)
+    small = plt.Rectangle((0.4, 0.4), 0.2, 0.2, facecolor="r", picker=5)
+    # Machinery for "receiving" events
+    received_events = []
+    def on_pick(event):
+        received_events.append(event)
+    plt.gcf().canvas.mpl_connect('pick_event', on_pick)
+    # Shortcut
+    rectangles_on_axes = (big_on_axes, small_on_axes)
+    # Axes setup
+    axes = {"gca": None, "host": None, "parasite": None}
+    if "gca" in rectangles_on_axes:
+        axes["gca"] = plt.gca()
+    if "host" in rectangles_on_axes or "parasite" in rectangles_on_axes:
+        axes["host"] = host_subplot(111)
+        axes["parasite"] = axes["host"].twin()
+    # Add rectangles to axes
+    axes[big_on_axes].add_patch(big)
+    axes[small_on_axes].add_patch(small)
+    # Simulate picking with click mouse event
+    if click_on == "big":
+        click_axes = axes[big_on_axes]
+        axes_coords = (0.3, 0.3)
+    else:
+        click_axes = axes[small_on_axes]
+        axes_coords = (0.5, 0.5)
+    # In reality mouse events never happen on parasite axes, only host axes
+    if click_axes is axes["parasite"]:
+        click_axes = axes["host"]
+    (x, y) = click_axes.transAxes.transform(axes_coords)
+    m = MouseEvent("button_press_event", click_axes.figure.canvas, x, y,
+                   button=1)
+    click_axes.pick(m)
+    # Checks
+    expected_n_events = 2 if click_on == "small" else 1
+    assert len(received_events) == expected_n_events
+    event_rects = [event.artist for event in received_events]
+    assert big in event_rects
+    if click_on == "small":
+        assert small in event_rects