matplotlib · timhoffm · Apr 15, 2021 · Nov 22, 2017 · Nov 30, 2017 · Jan 7, 2018
diff --git a/doc/users/next_whats_new/annulus.rst b/doc/users/next_whats_new/annulus.rst
@@ -0,0 +1,17 @@
+Add ``Annulus`` patch
+---------------------
+
+A new class for drawing elliptical annuli.
+
+.. plot::
+
+    import matplotlib.pyplot as plt
+    from matplotlib.patches import Annulus
+
+    fig, ax = plt.subplots()
+    cir = Annulus((0.5, 0.5), 0.2, 0.05, fc='g')        # circular annulus
+    ell = Annulus((0.5, 0.5), (0.5, 0.3), 0.1, 45,      # elliptical
+                fc='m', ec='b', alpha=0.5, hatch='xxx') 
+    ax.add_patch(cir)
+    ax.add_patch(ell)
+    ax.set_aspect('equal')
diff --git a/lib/matplotlib/patches.py b/lib/matplotlib/patches.py
@@ -1552,9 +1552,191 @@ def get_angle(self):
     angle = property(get_angle, set_angle)
 
 
-class Circle(Ellipse):
-    """A circle patch."""
+class Annulus(Patch):
+    """
+    An elliptical annulus.
+    """
+
+    @docstring.dedent_interpd
+    def __init__(self, xy, r, width, angle=0.0, **kwargs):
+        """
+        xy : (float, float)
+            xy coordinates of annulus centre.
+        r : float or (float, float)
+            The radius, or semi-axes.
+                - If float: radius of the outer circle.
+                - If two floats: semi-major and -minor axes of outer ellipse.
+        width : float
+            Width (thickness) of the annular ring. The width is measured inward
+            from the outer ellipse so that for the inner ellipse the semi-axes
+            are given by `r - width`. `width` must be less than or equal to the
+            semi-minor axis.
+        angle : float, default=0
+            Rotation angle in degrees (anti-clockwise from the positive
+            x-axis). Ignored for circular annuli (ie. if *r* is a scalar).
 
+        Valid kwargs are:
+
+        %(Patch_kwdoc)s
+        """
+        super().__init__(**kwargs)
+
+        self.set_radii(r)
+        self.center = xy
+        self.width = width
+        self.angle = angle
+        self._path = None
+
+    def __str__(self):
+        if self.a == self.b:
+            r = self.a
+        else:
+            r = (self.a, self.b)
+
+        return "Annulus(xy=(%s, %s), r=%s, width=%s, angle=%s)" % \
+                (*self.center, r, self.width, self.angle)
+
+    def set_center(self, xy):
+        """
+        Set the center of the annulus.
+
+        Parameters
+        ----------
+        xy : (float, float)
+        """
+        self._center = xy
+        self._path = None
+        self.stale = True
+
+    def get_center(self):
+        """Return the center of the annulus."""
+        return self._center
+
+    center = property(get_center, set_center)
+
+    def set_width(self, width):
+        """
+        Set the width (thickness) of the annulus ring. The width is measured
+        inwards from the outer ellipse.
+
+        Parameters
+        ----------
+        width : float
+        """
+        if min(self.a, self.b) <= width:
+            raise ValueError(
+                'Width of annulus must be less than or equal semi-minor axis')
+
+        self._width = width
+        self._path = None
+        self.stale = True
+
+    def get_width(self):
+        """
+        Return the width (thickness) of the annulus ring.
+        """
+        return self._width
+
+    width = property(get_width, set_width)
+
+    def set_angle(self, angle):
+        """
+        Set the tilt angle of the annulus.
+
+        Parameters
+        ----------
+        angle : float
+        """
+        self._angle = angle
+        self._path = None
+        self.stale = True
+
+    def get_angle(self):
+        """Return the angle of the annulus."""
+        return self._angle
+
+    angle = property(get_angle, set_angle)
+
+    def set_semimajor(self, a):
+        """
+        Set the semi-major axis *a* of the annulus.
+
+        Parameters
+        ----------
+        a : float
+        """
+        self.a = float(a)
+        self._path = None
+        self.stale = True
+
+    def set_semiminor(self, b):
+        """
+        Set the semi-minor axis *b* of the annulus.
+
+        Parameters
+        ----------
+        b : float
+        """
+        self.b = float(b)
+        self._path = None
+        self.stale = True
+
+    def set_radii(self, r):
+        """
+        Set the both the semi-major (*a*) and -minor radii (*b*) of the
+        annulus.
+
+        Parameters
+        ----------
+        r : (float, float)
+        """
+        if np.shape(r) == (2,):
+            self.a, self.b = r
+        elif np.shape(r) == ():
+            self.a = self.b = float(r)
+        else:
+            raise ValueError("Parameter 'r' must be one or two floats.")
+
+        self._path = None
+        self.stale = True
+
+    def get_radii(self):
+        return self.a, self.b
+
+    radii = property(get_radii, set_radii)
+
+    def _transform_verts(self, verts, a, b):
+        return transforms.Affine2D() \
+            .scale(*self._convert_xy_units((a, b))) \
+            .rotate_deg(self.angle) \
+            .translate(*self._convert_xy_units(self.center)) \
+            .transform(verts)
+
+    def _recompute_path(self):
+        # circular arc
+        arc = Path.arc(0, 360)
+
+        # annulus needs to draw an outer ring
+        # followed by a reversed and scaled inner ring
+        a, b, w = self.a, self.b, self.width
+        v1 = self._transform_verts(arc.vertices, a, b)
+        v2 = self._transform_verts(arc.vertices[::-1], a - w, b - w)
+        v = np.vstack([v1, v2, v1[0, :], (0, 0)])
+        c = np.hstack([arc.codes, Path.MOVETO,
+                       arc.codes[1:], Path.MOVETO,
+                       Path.CLOSEPOLY])
+        self._path = Path(v, c)
+
+    def get_path(self):
+        if self._path is None:
+            self._recompute_path()
+        return self._path
+
+
+class Circle(Ellipse):
+    """
+    A circle patch.
+    """
     def __str__(self):
         pars = self.center[0], self.center[1], self.radius
         fmt = "Circle(xy=(%g, %g), radius=%g)"

diff --git a/lib/matplotlib/tests/baseline_images/test_patches/annulus.png b/lib/matplotlib/tests/baseline_images/test_patches/annulus.png
diff --git a/lib/matplotlib/tests/test_patches.py b/lib/matplotlib/tests/test_patches.py
@@ -5,7 +5,8 @@
 from numpy.testing import assert_almost_equal, assert_array_equal
 import pytest
 
-from matplotlib.patches import Patch, Polygon, Rectangle, FancyArrowPatch
+from matplotlib.patches import (Annulus, Patch, Polygon, Rectangle,
+                                FancyArrowPatch)
 from matplotlib.testing.decorators import image_comparison, check_figures_equal
 from matplotlib.transforms import Bbox
 import matplotlib.pyplot as plt
@@ -333,6 +334,10 @@ def test_patch_str():
     expected = 'Arc(xy=(1, 2), width=3, height=4, angle=5, theta1=6, theta2=7)'
     assert str(p) == expected
 
+    p = mpatches.Annulus(xy=(1, 2), r=(3, 4), width=1, angle=2)
+    expected = "Annulus(xy=(1, 2), r=(3, 4), width=1, angle=2)"
+    assert str(p) == expected
+
     p = mpatches.RegularPolygon((1, 2), 20, radius=5)
     assert str(p) == "RegularPolygon((1, 2), 20, radius=5, orientation=0)"
 
@@ -582,6 +587,39 @@ def test_rotated_arcs():
         ax.set_aspect("equal")
 
 
+@image_comparison(baseline_images=['annulus'], extensions=['png'])
+def test_annulus():
+
+    fig, ax = plt.subplots()
+    cir = Annulus((0.5, 0.5), 0.2, 0.05, fc='g')        # circular annulus
+    ell = Annulus((0.5, 0.5), (0.5, 0.3), 0.1, 45,      # elliptical
+                  fc='m', ec='b', alpha=0.5, hatch='xxx')
+    ax.add_patch(cir)
+    ax.add_patch(ell)
+    ax.set_aspect('equal')
+
+
+@image_comparison(baseline_images=['annulus'], extensions=['png'])
+def test_annulus_setters():
+
+    fig, ax = plt.subplots()
+    cir = Annulus((0., 0.), 0.2, 0.01, fc='g')   # circular annulus
+    ell = Annulus((0., 0.), (1, 2), 0.1, 0,      # elliptical
+                  fc='m', ec='b', alpha=0.5, hatch='xxx')
+    ax.add_patch(cir)
+    ax.add_patch(ell)
+    ax.set_aspect('equal')
+
+    cir.center = (0.5, 0.5)
+    cir.radii = 0.2
+    cir.width = 0.05
+
+    ell.center = (0.5, 0.5)
+    ell.radii = (0.5, 0.3)
+    ell.width = 0.1
+    ell.angle = 45
+
+
 def test_degenerate_polygon():
     point = [0, 0]
     correct_extents = Bbox([point, point]).extents