Backport PR matplotlib#22254: Disable QuadMesh cursor data by default

tacaswell · meeseeksmachine · commit 61d4f69f457d · 2022-01-20T20:45:04.000Z
diff --git a/doc/api/next_api_changes/behavior/22254-DS.rst b/doc/api/next_api_changes/behavior/22254-DS.rst
@@ -0,0 +1,5 @@
+QuadMesh cursor data disabled by default
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Showing the cursor data of a `.QuadMesh` is now disabled by default, as it has
+significant performance issues with large meshes. To manually enable this
+use :meth:`.QuadMesh.set_show_cursor_data`.
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -2011,6 +2011,7 @@ def __init__(self, *args, **kwargs):
         self._shading = shading
         self._bbox = transforms.Bbox.unit()
         self._bbox.update_from_data_xy(self._coordinates.reshape(-1, 2))
+        self._show_cursor_data = False
         # super init delayed after own init because array kwarg requires
         # self._coordinates and self._shading
         super().__init__(**kwargs)
@@ -2207,7 +2208,23 @@ def draw(self, renderer):
         renderer.close_group(self.__class__.__name__)
         self.stale = False
 
+    def set_show_cursor_data(self, show_cursor_data):
+        """
+        Set whether cursor data should be shown.
+
+        Notes
+        -----
+        This is set to `False` by default for new quad meshes. Showing cursor
+        data can have significant performance impacts for large meshes.
+        """
+        self._show_cursor_data = show_cursor_data
+
+    def get_show_cursor_data(self):
+        return self._show_cursor_data
+
     def get_cursor_data(self, event):
+        if not self._show_cursor_data:
+            return
         contained, info = self.contains(event)
         if len(info["ind"]) == 1:
             ind, = info["ind"]
diff --git a/lib/matplotlib/tests/test_collections.py b/lib/matplotlib/tests/test_collections.py
@@ -1032,13 +1032,20 @@ def test_quadmesh_cursor_data():
     fig, ax = plt.subplots()
     *_, qm = ax.hist2d(
         np.arange(11)**2, 100 + np.arange(11)**2)  # width-10 bins
+
     x, y = ax.transData.transform([1, 101])
     event = MouseEvent('motion_notify_event', fig.canvas, x, y)
+
+    assert qm.get_show_cursor_data() is False
+    assert qm.get_cursor_data(event) is None
+
+    qm.set_show_cursor_data(True)
     assert qm.get_cursor_data(event) == 4  # (0**2, 1**2, 2**2, 3**2)
-    for out_xydata in []:
-        x, y = ax.transData.transform([-1, 101])
-        event = MouseEvent('motion_notify_event', fig.canvas, x, y)
-        assert qm.get_cursor_data(event) is None
+
+    # Outside the quadmesh bounds
+    x, y = ax.transData.transform([-1, 101])
+    event = MouseEvent('motion_notify_event', fig.canvas, x, y)
+    assert qm.get_cursor_data(event) is None
 
 
 def test_get_segments():
