Backport PR matplotlib#32228: Fixed a bug with drawing an empty Collection

Author: ksunden

lib/matplotlib/collections.py

@@ -363,6 +363,12 @@ def draw(self, renderer):
             return
         renderer.open_group(self.__class__.__name__, self.get_gid())
 
+        # Bail if the collection does not have any offsets (e.g., an empty scatter plot)
+        if len(self.get_offsets()) == 0:
+            renderer.close_group(self.__class__.__name__)
+            self.stale = False
+            return
+
         self.update_scalarmappable()
 
         transform, offset_trf, offsets, paths = self._prepare_points()

lib/matplotlib/tests/test_axes.py

@@ -3220,6 +3220,24 @@ def test_scatter_singular_plural_arguments(self):
                         facecolors=["#ffffff", "#000000", "#f0f0f0"],
                             facecolor="#ffffff")
 
+    @pytest.mark.parametrize('edgecolor, facecolor, linestyle',
+                             [('red', 'blue', 'solid'),
+                              ('red', 'blue', 'dashed'),
+                              ('red', 'none', 'solid'),
+                              ('none', 'blue', 'solid')])
+    @check_figures_equal()
+    def test_empty_scatter(self, fig_test, fig_ref, edgecolor, facecolor, linestyle):
+        # Verify that a spurious marker is not plotted in the bottom-left corner
+        # https://github.com/matplotlib/matplotlib/issues/32219
+        ax_test = fig_test.subplots()
+        ax_test.scatter([], [], ec=edgecolor, fc=facecolor, ls=linestyle, clip_on=False)
+        ax_test.set_xlim(0, 1)
+        ax_test.set_ylim(0, 1)
+
+        ax_ref = fig_ref.subplots()
+        ax_ref.set_xlim(0, 1)
+        ax_ref.set_ylim(0, 1)
+
 
 def _params(c=None, xsize=2, *, edgecolors=None, **kwargs):
     return (c, edgecolors, kwargs, xsize)