Disable QuadMesh cursor data by default

dstansby · dstansby · commit 071e62f60bde · 2022-01-17T19:54:34.000Z
diff --git a/doc/api/next_api_changes/behavior/xxxxx-DS.rst b/doc/api/next_api_changes/behavior/xxxxx-DS.rst
@@ -0,0 +1,3 @@
+Showing the cursor data of a `.QaudMesh` is now disabled by default, as it has
+significant performance issues with large meshes. To manually enable this
+set ``my_quad_mesh.show_cursor_data = True``.
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -1934,6 +1934,12 @@ class QuadMesh(Collection):
 
     shading : {'flat', 'gouraud'}, default: 'flat'
 
+    Attributes
+    ----------
+    show_cursor_data : bool
+        Whether to show cursor data on an interactive plot. For large
+        QuadMeshes this is currently extermely show, so is disabled by default.
+
     Notes
     -----
     Unlike other `.Collection`\s, the default *pickradius* of `.QuadMesh` is 0,
@@ -2000,6 +2006,7 @@ 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)
@@ -2198,6 +2205,8 @@ def draw(self, renderer):
         self.stale = False
 
     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
@@ -1027,13 +1027,16 @@ 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_cursor_data(event) is None
+    qm.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
+
+    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():

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Showing the cursor data of a `.QaudMesh` is now disabled by default, as it has
	`2`	`+significant performance issues with large meshes. To manually enable this`
	`3`	+set ``my_quad_mesh.show_cursor_data = True``.