matplotlib · jklymak · Aug 2, 2021
diff --git a/doc/api/next_api_changes/deprecations/20777-JMK.rst b/doc/api/next_api_changes/deprecations/20777-JMK.rst
@@ -0,0 +1,7 @@
+dpi keyword argument of collections.set_sizes is removed
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The *dpi* argument of `.PathCollection.set_sizes`, `.PolyCollection.set_sizes`,
+`.RegularPolyCollection.set_sizes`, `.CircleCollection.set_sizes` no longer has 
+an effect.  The dpi is determined by *dpi_scale_trans* property of `.FigureBase`, 
+which works with subfigures.
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -947,6 +947,7 @@ def get_sizes(self):
         """
         return self._sizes
 
+    @_api.delete_parameter("3.5", "dpi")
     def set_sizes(self, sizes, dpi=72.0):
         """
         Set the sizes of each member of the collection.
@@ -956,15 +957,17 @@ def set_sizes(self, sizes, dpi=72.0):
         sizes : ndarray or None
             The size to set for each element of the collection.  The
             value is the 'area' of the element.
-        dpi : float, default: 72
-            The dpi of the canvas.
         """
         if sizes is None:
             self._sizes = np.array([])
             self._transforms = np.empty((0, 3, 3))
         else:
             self._sizes = np.asarray(sizes)
             self._transforms = np.zeros((len(self._sizes), 3, 3))
+            dpi = 72.0
+            if self.figure is not None:
+                trans = self.figure.dpi_scale_trans
+                dpi = trans.transform(np.array([1, 1]))[0]
             scale = np.sqrt(self._sizes) * dpi / 72.0 * self._factor
             self._transforms[:, 0, 0] = scale
             self._transforms[:, 1, 1] = scale
@@ -973,7 +976,7 @@ def set_sizes(self, sizes, dpi=72.0):
 
     @artist.allow_rasterization
     def draw(self, renderer):
-        self.set_sizes(self._sizes, self.figure.dpi)
+        self.set_sizes(self._sizes)
         super().draw(renderer)
 
 
@@ -1335,7 +1338,7 @@ def get_rotation(self):
 
     @artist.allow_rasterization
     def draw(self, renderer):
-        self.set_sizes(self._sizes, self.figure.dpi)
+        self.set_sizes(self._sizes)
         self._transforms = [
             transforms.Affine2D(x).rotate(-self._rotation).get_matrix()
             for x in self._transforms

diff --git a/lib/matplotlib/tests/baseline_images/test_figure/test_subfigure_scatter_size.png b/lib/matplotlib/tests/baseline_images/test_figure/test_subfigure_scatter_size.png
diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
@@ -1031,6 +1031,23 @@ def test_subfigure_spanning():
     np.testing.assert_allclose(sub_figs[2].bbox.max, [w, h / 3])
 
 
+@image_comparison(['test_subfigure_scatter_size.png'], style='mpl20',
+                  remove_text=True)
+def test_subfigure_scatter_size():
+    # markers in the left- and right-most subplots should be the same
+    fig = plt.figure()
+    gs = fig.add_gridspec(1, 2)
+    ax0 = fig.add_subplot(gs[1])
+    ax0.scatter([1, 2, 3], [1, 2, 3], s=30, marker='s')
+    ax0.scatter([3, 4, 5], [1, 2, 3], s=[20, 30, 40], marker='s')
+
+    sfig = fig.add_subfigure(gs[0])
+    axs = sfig.subplots(1, 2)
+    for ax in [ax0, axs[0]]:
+        ax.scatter([1, 2, 3], [1, 2, 3], s=30, marker='s', color='r')
+        ax.scatter([3, 4, 5], [1, 2, 3], s=[20, 30, 40], marker='s', color='g')
+
+
 def test_add_subplot_kwargs():
     # fig.add_subplot() always creates new axes, even if axes kwargs differ.
     fig = plt.figure()

diff --git a/lib/mpl_toolkits/mplot3d/art3d.py b/lib/mpl_toolkits/mplot3d/art3d.py
@@ -568,8 +568,9 @@ def set_3d_properties(self, zs, zdir):
         self._vzs = None
         self.stale = True
 
+    @_api.delete_parameter("3.5", "dpi")
     def set_sizes(self, sizes, dpi=72.0):
-        super().set_sizes(sizes, dpi)
+        super().set_sizes(sizes)
         if not self._in_draw:
             self._sizes3d = sizes
 
@@ -607,7 +608,7 @@ def do_3d_projection(self, renderer=None):
 
         # we have to special case the sizes because of code in collections.py
         # as the draw method does
-        #      self.set_sizes(self._sizes, self.figure.dpi)
+        #      self.set_sizes(self._sizes)
         # so we can not rely on doing the sorting on the way out via get_*
 
         if len(self._sizes3d) > 1: