DEP: PolyQuadMesh warn when setting with a compressed array

greglucas · greglucas · commit 19d495128482 · 2023-05-06T07:58:40.000-06:00
Previously to update a pcolor array you would need to set only the
compressed values. This required keeping track of the mask by the user.
For consistency with QuadMesh, we should only accept full 2D arrays
that include the mask if a user desires. This also allows for the
mask to be updated when setting an array.
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -2311,9 +2311,21 @@ def get_facecolor(self):
         return fc[unmasked_polys, :]
 
     def set_array(self, A):
-        prev_mask = self._get_unmasked_polys()
+        prev_unmask = self._get_unmasked_polys()
+        # MPL <3.8 compressed the mask, so we need to handle flattened 1d input
+        # until the deprecation expires, also only warning when there are masked
+        # elements and thus compression occurring.
+        if (np.ndim(A) == 1 and not np.all(prev_unmask) and
+                len(A) == np.sum(prev_unmask)):
+            _api.warn_deprecated("3.8", message="Setting a PolyQuadMesh array using "
+                                 "the compressed values is deprecated. "
+                                 "Pass the full 2D shape of the original array "
+                                 f"{prev_unmask.shape} including the masked elements.")
+            Afull = np.empty(prev_unmask.shape)
+            Afull[prev_unmask] = A
+            A = np.ma.array(Afull, mask=~prev_unmask)
         super().set_array(A)
         # If the mask has changed at all we need to update
         # the set of Polys that we are drawing
-        if not np.array_equal(prev_mask, self._get_unmasked_polys()):
+        if not np.array_equal(prev_unmask, self._get_unmasked_polys()):
             self._set_unmasked_verts()
diff --git a/lib/matplotlib/tests/test_collections.py b/lib/matplotlib/tests/test_collections.py
@@ -918,6 +918,11 @@ def test_polyquadmesh_masked_vertices_array():
     polymesh.update_scalarmappable()
     assert len(polymesh.get_paths()) == 4
 
+    # Setting array with 1D compressed values is deprecated
+    with pytest.warns(mpl.MatplotlibDeprecationWarning,
+                      match="Setting a PolyQuadMesh"):
+        polymesh.set_array(np.ones(4))
+
 
 def test_quadmesh_get_coordinates(pcfunc):
     x = [0, 1, 2]
