Backport PR matplotlib#22946: FIX: Handle no-offsets in collection datalim (alternative)

Author: timhoffm

lib/matplotlib/collections.py

@@ -61,7 +61,6 @@ class Collection(artist.Artist, cm.ScalarMappable):
     mappable will be used to set the ``facecolors`` and ``edgecolors``,
     ignoring those that were manually passed in.
     """
-    _offsets = np.zeros((0, 2))
     #: Either a list of 3x3 arrays or an Nx3x3 array (representing N
     #: transforms), suitable for the `all_transforms` argument to
     #: `~matplotlib.backend_bases.RendererBase.draw_path_collection`;
@@ -193,15 +192,11 @@ def __init__(self,
         else:
             self._joinstyle = None
 
-        # default to zeros
-        self._offsets = np.zeros((1, 2))
-
         if offsets is not None:
             offsets = np.asanyarray(offsets, float)
             # Broadcast (2,) -> (1, 2) but nothing else.
             if offsets.shape == (2,):
                 offsets = offsets[None, :]
-            self._offsets = offsets
         elif transOffset is not None:
             _api.warn_deprecated(
                 '3.5',
@@ -215,6 +210,7 @@ def __init__(self,
                         'explicitly.')
             transOffset = None
 
+        self._offsets = offsets
         self._transOffset = transOffset
 
         self._path_effects = None
@@ -273,9 +269,12 @@ def get_datalim(self, transData):
             # if there are offsets but in some coords other than data,
             # then don't use them for autoscaling.
             return transforms.Bbox.null()
-        offsets = self._offsets
+        offsets = self.get_offsets()
 
         paths = self.get_paths()
+        if not len(paths):
+            # No paths to transform
+            return transforms.Bbox.null()
 
         if not transform.is_affine:
             paths = [transform.transform_path_non_affine(p) for p in paths]
@@ -284,22 +283,22 @@ def get_datalim(self, transData):
             # transforms.get_affine().contains_branch(transData).  But later,
             # be careful to only apply the affine part that remains.
 
-        if isinstance(offsets, np.ma.MaskedArray):
-            offsets = offsets.filled(np.nan)
+        if any(transform.contains_branch_seperately(transData)):
+            if isinstance(offsets, np.ma.MaskedArray):
+                offsets = offsets.filled(np.nan)
             # get_path_collection_extents handles nan but not masked arrays
-
-        if len(paths) and len(offsets):
-            if any(transform.contains_branch_seperately(transData)):
-                # collections that are just in data units (like quiver)
-                # can properly have the axes limits set by their shape +
-                # offset.  LineCollections that have no offsets can
-                # also use this algorithm (like streamplot).
-                return mpath.get_path_collection_extents(
-                    transform.get_affine() - transData, paths,
-                    self.get_transforms(),
-                    transOffset.transform_non_affine(offsets),
-                    transOffset.get_affine().frozen())
-
+            # collections that are just in data units (like quiver)
+            # can properly have the axes limits set by their shape +
+            # offset.  LineCollections that have no offsets can
+            # also use this algorithm (like streamplot).
+            return mpath.get_path_collection_extents(
+                transform.get_affine() - transData, paths,
+                self.get_transforms(),
+                transOffset.transform_non_affine(offsets),
+                transOffset.get_affine().frozen())
+
+        # NOTE: None is the default case where no offsets were passed in
+        if self._offsets is not None:
             # 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
@@ -325,7 +324,7 @@ def _prepare_points(self):
 
         transform = self.get_transform()
         transOffset = self.get_offset_transform()
-        offsets = self._offsets
+        offsets = self.get_offsets()
         paths = self.get_paths()
 
         if self.have_units():
@@ -336,10 +335,9 @@ def _prepare_points(self):
                 xs = self.convert_xunits(xs)
                 ys = self.convert_yunits(ys)
                 paths.append(mpath.Path(np.column_stack([xs, ys]), path.codes))
-            if offsets.size:
-                xs = self.convert_xunits(offsets[:, 0])
-                ys = self.convert_yunits(offsets[:, 1])
-                offsets = np.column_stack([xs, ys])
+            xs = self.convert_xunits(offsets[:, 0])
+            ys = self.convert_yunits(offsets[:, 1])
+            offsets = np.column_stack([xs, ys])
 
         if not transform.is_affine:
             paths = [transform.transform_path_non_affine(path)
@@ -569,7 +567,8 @@ def set_offsets(self, offsets):
 
     def get_offsets(self):
         """Return the offsets for the collection."""
-        return self._offsets
+        # Default to zeros in the no-offset (None) case
+        return np.zeros((1, 2)) if self._offsets is None else self._offsets
 
     def _get_default_linewidth(self):
         # This may be overridden in a subclass.
@@ -2166,13 +2165,12 @@ def draw(self, renderer):
         renderer.open_group(self.__class__.__name__, self.get_gid())
         transform = self.get_transform()
         transOffset = self.get_offset_transform()
-        offsets = self._offsets
+        offsets = self.get_offsets()
 
         if self.have_units():
-            if len(self._offsets):
-                xs = self.convert_xunits(self._offsets[:, 0])
-                ys = self.convert_yunits(self._offsets[:, 1])
-                offsets = np.column_stack([xs, ys])
+            xs = self.convert_xunits(offsets[:, 0])
+            ys = self.convert_yunits(offsets[:, 1])
+            offsets = np.column_stack([xs, ys])
 
         self.update_scalarmappable()
 

lib/matplotlib/tests/test_collections.py

@@ -9,6 +9,7 @@
 import matplotlib.pyplot as plt
 import matplotlib.collections as mcollections
 import matplotlib.colors as mcolors
+import matplotlib.path as mpath
 import matplotlib.transforms as mtransforms
 from matplotlib.collections import (Collection, LineCollection,
                                     EventCollection, PolyCollection)
@@ -291,6 +292,17 @@ def test_null_collection_datalim():
                        mtransforms.Bbox.null().get_points())
 
 
+def test_no_offsets_datalim():
+    # A collection with no offsets and a non transData
+    # transform should return a null bbox
+    ax = plt.axes()
+    coll = mcollections.PathCollection([mpath.Path([(0, 0), (1, 0)])])
+    ax.add_collection(coll)
+    coll_data_lim = coll.get_datalim(mtransforms.IdentityTransform())
+    assert_array_equal(coll_data_lim.get_points(),
+                       mtransforms.Bbox.null().get_points())
+
+
 def test_add_collection():
     # Test if data limits are unchanged by adding an empty collection.
     # GitHub issue #1490, pull #1497.