Alpha argument added to BezierTriangle and CurvedPolygon plotting functions

src/python/bezier/_plot_helpers.py

@@ -62,14 +62,15 @@ def add_plot_boundary(ax, padding=0.125):
     )
 
 
-def add_patch(ax, color, pts_per_edge, *edges):
+def add_patch(ax, color, pts_per_edge, *edges, alpha=None):
     """Add a polygonal surface patch to a plot.
 
     Args:
         ax (matplotlib.artist.Artist): A matplotlib axis.
         color (Tuple[float, float, float]): Color as RGB profile.
         pts_per_edge (int): Number of points to use in polygonal
             approximation of edge.
+        alpha (Optional[float]): Alpha value of patch centre, between 0 and 1 inclusive.
         *edges (Tuple[~bezier.curve.Curve, ...]): Curved edges defining
             a boundary.
     """
@@ -99,6 +100,6 @@ def add_patch(ax, color, pts_per_edge, *edges):
     # column but ``Path()`` wants ``x-y`` points in each row.
     path = _path_mod.Path(polygon.T)
     patch = patches.PathPatch(
-        path, facecolor=color, edgecolor=color, alpha=0.625
+        path, facecolor=color, edgecolor=color, alpha=(alpha or 0.625)
     )
     ax.add_patch(patch)

src/python/bezier/curved_polygon.py

@@ -259,20 +259,21 @@ def __repr__(self):
         """
         return f"<{self.__class__.__name__} (num_sides={self._num_sides:d})>"
 
-    def plot(self, pts_per_edge, color=None, ax=None):
+    def plot(self, pts_per_edge, color=None, ax=None, alpha=None):
         """Plot the current curved polygon.
 
         Args:
             pts_per_edge (int): Number of points to plot per curved edge.
             color (Optional[Tuple[float, float, float]]): Color as RGB profile.
             ax (Optional[matplotlib.artist.Artist]): matplotlib axis object
                 to add plot to.
+            alpha (Optional[float]): Alpha value of patch centre, between 0 and 1 inclusive.
 
         Returns:
             matplotlib.artist.Artist: The axis containing the plot. This
             may be a newly created axis.
         """
         if ax is None:
             ax = _plot_helpers.new_axis()
-        _plot_helpers.add_patch(ax, color, pts_per_edge, *self._edges)
+        _plot_helpers.add_patch(ax, color, pts_per_edge, *self._edges, alpha=alpha)
         return ax

src/python/bezier/triangle.py

@@ -701,7 +701,7 @@ def evaluate_cartesian_multi(self, param_vals, verify=True):
             self._nodes, self._degree, param_vals, self._dimension
         )
 
-    def plot(self, pts_per_edge, color=None, ax=None, with_nodes=False):
+    def plot(self, pts_per_edge, color=None, ax=None, with_nodes=False, alpha=None):
         """Plot the current triangle.
 
         Args:
@@ -711,6 +711,7 @@ def plot(self, pts_per_edge, color=None, ax=None, with_nodes=False):
                 to add plot to.
             with_nodes (Optional[bool]): Determines if the control points
                 should be added to the plot. Off by default.
+            alpha (Optional[float]): Alpha value of patch centre, between 0 and 1 inclusive.
 
         Returns:
             matplotlib.artist.Artist: The axis containing the plot. This
@@ -728,7 +729,7 @@ def plot(self, pts_per_edge, color=None, ax=None, with_nodes=False):
 
         if ax is None:
             ax = _plot_helpers.new_axis()
-        _plot_helpers.add_patch(ax, color, pts_per_edge, *self._get_edges())
+        _plot_helpers.add_patch(ax, color, pts_per_edge, *self._get_edges(), alpha=alpha)
         if with_nodes:
             ax.plot(
                 self._nodes[0, :],

tests/unit/test__plot_helpers.py

@@ -86,10 +86,10 @@ def test_with_padding(self):
 
 class Test_add_patch(utils.NumPyTestCase):
     @staticmethod
-    def _call_function_under_test(ax, color, pts_per_edge, *edges):
+    def _call_function_under_test(ax, color, pts_per_edge, *edges, alpha=None):
         from bezier import _plot_helpers
 
-        return _plot_helpers.add_patch(ax, color, pts_per_edge, *edges)
+        return _plot_helpers.add_patch(ax, color, pts_per_edge, *edges, alpha=alpha)
 
     def _path_val(self, path, expected_transpose):
         self.assertEqual(path.Path.call_count, 1)
@@ -143,7 +143,7 @@ def test_it(self):
             "matplotlib.path": path,
         }
         func = functools.partial(
-            self._call_function_under_test, ax, color, pts_per_edge, *edges
+            self._call_function_under_test, ax, color, pts_per_edge, *edges, alpha=0.5
         )
         result = run_fake_modules(modules, func)
         self.assertIsNone(result)
@@ -153,7 +153,7 @@ def test_it(self):
             path.Path.return_value,
             facecolor=color,
             edgecolor=color,
-            alpha=0.625,
+            alpha=0.5,
         )
         ax.add_patch.assert_called_once_with(patches.PathPatch.return_value)
         line.get_color.assert_called_once_with()

tests/unit/test_curved_polygon.py

@@ -130,7 +130,7 @@ def test_plot_defaults(self, add_patch_mock, new_axis_mock):
         # Verify mocks.
         new_axis_mock.assert_called_once_with()
         add_patch_mock.assert_called_once_with(
-            ax, None, pts_per_edge, *curved_poly._edges
+            ax, None, pts_per_edge, *curved_poly._edges, alpha=None
         )
 
     @unittest.mock.patch("bezier._plot_helpers.new_axis")
@@ -140,10 +140,11 @@ def test_plot_explicit(self, add_patch_mock, new_axis_mock):
         color = (0.5, 0.5, 0.5)
         curved_poly = self._make_default()
         pts_per_edge = 16
-        result = curved_poly.plot(pts_per_edge, color=color, ax=ax)
+        alpha = 0.5
+        result = curved_poly.plot(pts_per_edge, color=color, ax=ax, alpha=alpha)
         self.assertIs(result, ax)
         # Verify mocks.
         new_axis_mock.assert_not_called()
         add_patch_mock.assert_called_once_with(
-            ax, color, pts_per_edge, *curved_poly._edges
+            ax, color, pts_per_edge, *curved_poly._edges, alpha=alpha
         )

tests/unit/test_triangle.py

@@ -463,7 +463,7 @@ def test_plot_defaults(self, add_patch_mock, new_axis_mock):
         # Verify mocks.
         new_axis_mock.assert_called_once_with()
         add_patch_mock.assert_called_once_with(
-            ax, None, pts_per_edge, *curve._edges
+            ax, None, pts_per_edge, *curve._edges, alpha=None
         )
 
     @unittest.mock.patch("bezier._plot_helpers.new_axis")
@@ -473,12 +473,13 @@ def test_plot_explicit(self, add_patch_mock, new_axis_mock):
         color = (0.5, 0.5, 0.5)
         curve = self._make_one(self.UNIT_TRIANGLE, 1, copy=False)
         pts_per_edge = 16
-        result = curve.plot(pts_per_edge, color=color, ax=ax, with_nodes=True)
+        alpha = 0.5
+        result = curve.plot(pts_per_edge, color=color, ax=ax, with_nodes=True, alpha=alpha)
         self.assertIs(result, ax)
         # Verify mocks.
         new_axis_mock.assert_not_called()
         add_patch_mock.assert_called_once_with(
-            ax, color, pts_per_edge, *curve._edges
+            ax, color, pts_per_edge, *curve._edges, alpha=alpha
         )
         # Check the call to ax.plot(). We can't assert_any_call()
         # since == breaks on NumPy arrays.