Fix: Prevent Cursor blitting from erasing overlapping axes

MohitPal2005 · web-flow · commit 7c7e251444c7 · 2026-03-30T18:32:40.000-04:00
* Fix: Prevent Cursor blitting from erasing overlapping axes

* Fix styling: remove trailing whitespace and shorten comment

* MAINT: explicitly mark Cursor blitting on overlapping axes as unsupported

* style: fix ruff line length limit in widgets.py

* test: add coverage for cursor overlapping axes warning

* chore: trigger CI to clear Windows timeout flake
diff --git a/lib/matplotlib/tests/test_widgets.py b/lib/matplotlib/tests/test_widgets.py
@@ -1817,3 +1817,19 @@ def test_parent_axes_removal():
     evt = DrawEvent('draw_event', fig.canvas, renderer)
     radio._clear(evt)
     checks._clear(evt)
+
+
+def test_cursor_overlapping_axes_blitting_warning():
+    """Test that a warning is raised and useblit is disabled for overlapping axes."""
+    fig = plt.figure()
+    ax1 = fig.add_axes([0.1, 0.1, 0.8, 0.8])
+    ax2 = fig.add_axes([0.2, 0.2, 0.6, 0.6])  # Explicitly overlaps ax1
+
+    match_text = (
+        "Cursor blitting is currently not supported on "
+        "overlapping axes"
+    )
+    with pytest.warns(UserWarning, match=match_text):
+        cursor = widgets.Cursor(ax1, useblit=True)
+
+    assert cursor.useblit is False
diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
@@ -2084,6 +2084,16 @@ def __init__(self, ax, *, horizOn=True, vertOn=True, useblit=False,
         self.vertOn = vertOn
         self.useblit = useblit and self.canvas.supports_blit  # TODO: make dynamic
 
+        if self.useblit:
+            for ax_ in ax.get_figure(root=True).get_axes():
+                if ax_ is not ax and ax.bbox.overlaps(ax_.bbox):
+                    _api.warn_external(
+                        "Cursor blitting is currently not supported on "
+                        "overlapping axes; falling back to useblit=False."
+                    )
+                    self.useblit = False
+                    break
+
         if self.useblit:
             lineprops['animated'] = True
         self.lineh = ax.axhline(ax.get_ybound()[0], visible=False, **lineprops)
