FIX: Include (0, 0) offsets in scatter autoscaling

A scatter point at (0, 0) has offsets with 0s and any(offsets)
then gets evaluated to False. We still want to include this point
in the autoscaling if it is there.

Author: greglucas

lib/matplotlib/collections.py

@@ -258,9 +258,9 @@ def get_datalim(self, transData):
 
         transform = self.get_transform()
         offset_trf = self.get_offset_transform()
-        has_offsets = np.any(self._offsets)  # True if any non-zero offsets
-        if has_offsets and not offset_trf.contains_branch(transData):
-            # if there are offsets but in some coords other than data,
+        if not (isinstance(offset_trf, transforms.IdentityTransform)
+                or offset_trf.contains_branch(transData)):
+            # if the offsets are in some coords other than data,
             # then don't use them for autoscaling.
             return transforms.Bbox.null()
         offsets = self._offsets
@@ -289,20 +289,19 @@ def get_datalim(self, transData):
                     self.get_transforms(),
                     offset_trf.transform_non_affine(offsets),
                     offset_trf.get_affine().frozen())
-            if has_offsets:
-                # this is for collections that have their paths (shapes)
-                # in physical, axes-relative, or figure-relative units
-                # (i.e. like scatter). We can't uniquely set limits based on
-                # those shapes, so we just set the limits based on their
-                # location.
-
-                offsets = (offset_trf - transData).transform(offsets)
-                # note A-B means A B^{-1}
-                offsets = np.ma.masked_invalid(offsets)
-                if not offsets.mask.all():
-                    bbox = transforms.Bbox.null()
-                    bbox.update_from_data_xy(offsets)
-                    return bbox
+
+            # this is for collections that have their paths (shapes)
+            # in physical, axes-relative, or figure-relative units
+            # (i.e. like scatter). We can't uniquely set limits based on
+            # those shapes, so we just set the limits based on their
+            # location.
+            offsets = (offset_trf - transData).transform(offsets)
+            # note A-B means A B^{-1}
+            offsets = np.ma.masked_invalid(offsets)
+            if not offsets.mask.all():
+                bbox = transforms.Bbox.null()
+                bbox.update_from_data_xy(offsets)
+                return bbox
         return transforms.Bbox.null()
 
     def get_window_extent(self, renderer):

lib/matplotlib/tests/test_collections.py

@@ -711,6 +711,22 @@ def test_singleton_autolim():
     np.testing.assert_allclose(ax.get_xlim(), [-0.06, 0.06])
 
 
+@pytest.mark.parametrize("transform, expected", [
+    ("transData", (-0.5, 3.5)),
+    ("transAxes", (2.8, 3.2)),
+])
+def test_autolim_with_zeros(transform, expected):
+    # 1) Test that a scatter at (0, 0) data coordinates contributes to
+    # autoscaling even though any(offsets) would be False in that situation.
+    # 2) Test that specifying transAxes for the transform does not contribute
+    # to the autoscaling.
+    fig, ax = plt.subplots()
+    ax.scatter(0, 0, transform=getattr(ax, transform))
+    ax.scatter(3, 3)
+    np.testing.assert_allclose(ax.get_ylim(), expected)
+    np.testing.assert_allclose(ax.get_xlim(), expected)
+
+
 @pytest.mark.parametrize('flat_ref, kwargs', [
     (True, {}),
     (False, {}),