ENH: Separate facecolor alpha and edgecolor alpha for patches

j1642 · j1642 · commit d54649338d60 · 2022-12-10T12:58:35.000-05:00
diff --git a/lib/matplotlib/patches.py b/lib/matplotlib/patches.py
@@ -314,7 +314,7 @@ def set_antialiased(self, aa):
         self._antialiased = aa
         self.stale = True
 
-    def _set_edgecolor(self, color):
+    def _set_edgecolor(self, color, edge_alpha=0):
         set_hatch_color = True
         if color is None:
             if (mpl.rcParams['patch.force_edgecolor'] or
@@ -323,8 +323,10 @@ def _set_edgecolor(self, color):
             else:
                 color = 'none'
                 set_hatch_color = False
-
-        self._edgecolor = colors.to_rgba(color, self._alpha)
+        if edge_alpha:
+            self._edgecolor = colors.to_rgba(color, edge_alpha)
+        else:
+            self._edgecolor = colors.to_rgba(color, self._alpha)
         if set_hatch_color:
             self._hatch_color = self._edgecolor
         self.stale = True
@@ -340,10 +342,13 @@ def set_edgecolor(self, color):
         self._original_edgecolor = color
         self._set_edgecolor(color)
 
-    def _set_facecolor(self, color):
+    def _set_facecolor(self, color, face_alpha=0):
         if color is None:
             color = mpl.rcParams['patch.facecolor']
-        alpha = self._alpha if self._fill else 0
+        if face_alpha and self._fill:
+            alpha = face_alpha
+        else:
+            alpha = self._alpha if self._fill else 0
         self._facecolor = colors.to_rgba(color, alpha)
         self.stale = True
 
@@ -375,11 +380,37 @@ def set_color(self, c):
         self.set_edgecolor(c)
 
     def set_alpha(self, alpha):
-        # docstring inherited
-        super().set_alpha(alpha)
-        self._set_facecolor(self._original_facecolor)
-        self._set_edgecolor(self._original_edgecolor)
-        # stale is already True
+        """
+        Set the alpha value used for blending.
+
+        Parameters
+        ----------
+        alpha : scalar or None or tuple of scalars
+            *alpha* must be within the 0-1 range, inclusive.
+        """
+        is_alpha_valid_tuple = False
+        if isinstance(alpha, tuple):
+            if len(alpha) != 2:
+                raise ValueError('If given as a tuple, alpha must contain two '
+                                 'numbers, the face and edge alpha values')
+            for item in alpha:
+                if not isinstance(item, Number):
+                    raise TypeError('Alpha values must be numbers between 0 '
+                                    'and 1, inclusive')
+                if not (0 <= item <= 1):
+                    raise ValueError('Alpha values must be between 0 and 1, '
+                                     'inclusive')
+            is_alpha_valid_tuple = True
+        if is_alpha_valid_tuple:
+            face_alpha = alpha[0]
+            edge_alpha = alpha[1]
+            self._set_facecolor(self._original_facecolor, face_alpha)
+            self._set_edgecolor(self._original_edgecolor, edge_alpha)
+        else:
+            super().set_alpha(alpha)
+            self._set_facecolor(self._original_facecolor)
+            self._set_edgecolor(self._original_edgecolor)
+            # stale is already True
 
     def set_linewidth(self, w):
         """
diff --git a/lib/matplotlib/tests/test_patches.py b/lib/matplotlib/tests/test_patches.py
@@ -880,3 +880,19 @@ def test_modifying_arc(fig_test, fig_ref):
     fig_test.subplots().add_patch(arc2)
     arc2.set_width(.5)
     arc2.set_angle(20)
+
+
+@check_figures_equal()
+def test_alpha_as_tuple(fig_test, fig_ref):
+    patch_test = Rectangle((0, 0), 1, 1,
+                           edgecolor='black',
+                           facecolor='red',
+                           alpha=(0.1, 1))
+    ax = fig_test.add_subplot(111)
+    ax.add_patch(patch_test)
+
+    patch_ref = Rectangle((0, 0), 1, 1,
+                          edgecolor='black',
+                          facecolor=(*mcolors.to_rgb('red'), 0.1))
+    ax = fig_ref.add_subplot(111)
+    ax.add_patch(patch_ref)
