Add parameter to use the center or a corner of the rectangle for the position

ericpre · ericpre · commit c92f106aaafb · 2024-04-02T18:18:04.000+01:00
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -1876,14 +1876,22 @@ class RectangleCollection(_CollectionWithWidthHeightAngle):
         refer to the *offsets* data units. 'xy' differs from all others in
         that the angle as plotted varies with the aspect ratio, and equals
         the specified angle only when the aspect ratio is unity.  Hence
-        it behaves the same as the `~.patches.Ellipse` with
+        it behaves the same as the `~.patches.Rectangle` with
         ``axes.transData`` as its transform.
+    centered : bool
+        Whether to use the center or the corner of the rectangle to
+        define the position of the rectangles. Default is False.
     **kwargs
         Forwarded to `Collection`.
 
     """
     _path_generator = mpath.Path.unit_rectangle
 
+    def __init__(self, *args, **kwargs):
+        if kwargs.pop("centered", False):
+            self._path_generator = mpath.Path.unit_rectangle_centered
+        super().__init__(*args, **kwargs)
+
 
 class PatchCollection(Collection):
     """
diff --git a/lib/matplotlib/path.py b/lib/matplotlib/path.py
@@ -741,6 +741,20 @@ def unit_rectangle(cls):
                                       closed=True, readonly=True)
         return cls._unit_rectangle
 
+    _unit_rectangle_centered = None
+
+    @classmethod
+    def unit_rectangle_centered(cls):
+        """
+        Return a `Path` instance of the unit rectangle from (-0.5, -0.5) to (0.5, 0.5).
+        """
+        if cls._unit_rectangle_centered is None:
+            cls._unit_rectangle_centered = cls(
+                [[-0.5, -0.5], [0.5, -0.5], [0.5, 0.5], [-0.5, 0.5], [-0.5, -0.5]],
+                closed=True, readonly=True
+                )
+        return cls._unit_rectangle_centered
+
     _unit_regular_polygons = WeakValueDictionary()
 
     @classmethod
diff --git a/lib/matplotlib/tests/test_collections.py b/lib/matplotlib/tests/test_collections.py
@@ -431,10 +431,12 @@ def test_RectangleCollection():
 
 
 @pytest.mark.parametrize(
-    'Class,scale',
-    [(mcollections.EllipseCollection, 0.5), (mcollections.RectangleCollection, 1)]
+    'Class, scale, centered',
+    [(mcollections.EllipseCollection, 0.5, None),
+     (mcollections.RectangleCollection, 1, False),
+     (mcollections.RectangleCollection, 1, True)]
     )
-def test_WidthHeightAngleCollection_setter_getter(Class, scale):
+def test_WidthHeightAngleCollection_setter_getter(Class, scale, centered):
     # Test widths, heights and angle setter
     rng = np.random.default_rng(0)
 
@@ -445,13 +447,17 @@ def test_WidthHeightAngleCollection_setter_getter(Class, scale):
 
     fig, ax = plt.subplots()
 
+    kwargs = {}
+    if centered is not None:
+        kwargs["centered"] = centered
     ec = Class(
         widths=widths,
         heights=heights,
         angles=angles,
         offsets=offsets,
         units='x',
         offset_transform=ax.transData,
+        **kwargs,
         )
 
     assert_array_almost_equal(ec._widths, np.array(widths).ravel() * scale)
