Add configuration of Shadow and pie shadow

Author: oscargus

doc/users/next_whats_new/pie_shadow_control.rst

@@ -0,0 +1,5 @@
+The pie chart shadow can be controlled
+--------------------------------------
+
+The *shadow* argument to `~.Axes.pie` can now be a dict, allowing more control
+of the `.Shadow`-patch used.

doc/users/next_whats_new/shadow_shade.rst

@@ -0,0 +1,6 @@
+Shadow shade can be controlled
+------------------------------
+
+The `.Shadow` patch now has a *shade* argument to control the shadow darkness.
+If 1, the shadow is black, if 0, the shadow has the same color as the patch that
+is shadowed. The default value, which earlier was fixed, is 0.7.

galleries/examples/pie_and_polar_charts/pie_demo2.py

@@ -1,4 +1,6 @@
 """
+.. redirect-from:: gallery/pie_and_polar_charts/pie_demo2
+
 ==========
 Pie charts
 ==========
@@ -88,7 +90,7 @@
 
 fig, ax = plt.subplots()
 ax.pie(sizes, explode=explode, labels=labels, autopct='%1.1f%%',
-        shadow=True, startangle=90)
+       shadow=True, startangle=90)
 plt.show()
 
 # %%
@@ -97,6 +99,31 @@
 # slices are rotated counter-clockwise by 90 degrees, and the frog slice starts
 # on the positive y-axis.
 #
+# Controlling the size
+# --------------------
+#
+# By changing the *radius* parameter, and often the text size for better visual
+# appearance, the pie chart can be scaled.
+
+fig, ax = plt.subplots()
+
+ax.pie(sizes, labels=labels, autopct='%.0f%%',
+       textprops={'size': 'smaller'}, radius=0.5)
+plt.show()
+
+# %%
+# Modifying the shadow
+# --------------------
+#
+# The *shadow* parameter may optionally take a dictionary with arguments to
+# the `.Shadow` patch. This can be used to modify the default shadow.
+
+fig, ax = plt.subplots()
+ax.pie(sizes, explode=explode, labels=labels, autopct='%1.1f%%',
+       shadow={'ox': -0.04, 'edgecolor': 'none', 'shade': 0.9}, startangle=90)
+plt.show()
+
+# %%
 # .. admonition:: References
 #
 #    The use of the following functions, methods, classes and modules is shown

galleries/examples/pie_and_polar_charts/pie_features.py

@@ -3102,8 +3102,12 @@ def pie(self, x, explode=None, labels=None, colors=None,
             If set to ``None``, labels are not drawn but are still stored for
             use in `.legend`.
 
-        shadow : bool, default: False
-            Draw a shadow beneath the pie.
+        shadow : bool or dict, default: False
+            If bool, whether to draw a shadow beneath the pie. If dict, draw a shadow
+            passing the properties in the dict to `.Shadow`.
+
+            .. versionadded:: 3.8
+                *shadow* can be a dict.
 
         startangle : float, default: 0 degrees
             The angle by which the start of the pie is rotated,
@@ -3231,8 +3235,10 @@ def get_next_color():
             if shadow:
                 # Make sure to add a shadow after the call to add_patch so the
                 # figure and transform props will be set.
-                shad = mpatches.Shadow(w, -0.02, -0.02, label='_nolegend_')
-                self.add_patch(shad)
+                shadow_dict = {'ox': -0.02, 'oy': -0.02, 'label': '_nolegend_'}
+                if isinstance(shadow, dict):
+                    shadow_dict.update(shadow)
+                self.add_patch(mpatches.Shadow(w, **shadow_dict))
 
             if labeldistance is not None:
                 xt = x + labeldistance * radius * math.cos(thetam)

lib/matplotlib/axes/_axes.py

@@ -613,12 +613,12 @@ def __str__(self):
         return f"Shadow({self.patch})"
 
     @_docstring.dedent_interpd
-    def __init__(self, patch, ox, oy, **kwargs):
+    def __init__(self, patch, ox, oy, *, shade=0.7, **kwargs):
         """
         Create a shadow of the given *patch*.
 
         By default, the shadow will have the same face color as the *patch*,
-        but darkened.
+        but darkened. The darkness can be controlled by *shade*.
 
         Parameters
         ----------
@@ -627,6 +627,12 @@ def __init__(self, patch, ox, oy, **kwargs):
         ox, oy : float
             The shift of the shadow in data coordinates, scaled by a factor
             of dpi/72.
+        shade : float, default: 0.7
+            How the darkness of the shadow relates to the original color. If 1, the
+            shadow is black, if 0, the shadow has the same color as the *patch*.
+
+            .. versionadded:: 3.8
+
         **kwargs
             Properties of the shadow patch. Supported keys are:
 
@@ -638,7 +644,9 @@ def __init__(self, patch, ox, oy, **kwargs):
         self._shadow_transform = transforms.Affine2D()
 
         self.update_from(self.patch)
-        color = .3 * np.asarray(colors.to_rgb(self.patch.get_facecolor()))
+        if not 0 <= shade <= 1:
+            raise ValueError("shade must be between 0 and 1.")
+        color = (1 - shade) * np.asarray(colors.to_rgb(self.patch.get_facecolor()))
         self.update({'facecolor': color, 'edgecolor': color, 'alpha': 0.5,
                      # Place shadow patch directly behind the inherited patch.
                      'zorder': np.nextafter(self.patch.zorder, -np.inf),

lib/matplotlib/patches.py

@@ -5697,6 +5697,30 @@ def test_pie_nolabel_but_legend():
     plt.legend()
 
 
+@image_comparison(['pie_shadow.png'], style='mpl20')
+def test_pie_shadow():
+    # Also acts as a test for the shade argument of Shadow
+    sizes = [15, 30, 45, 10]
+    colors = ['yellowgreen', 'gold', 'lightskyblue', 'lightcoral']
+    explode = (0, 0.1, 0, 0)  # only "explode" the 2nd slice
+    _, axes = plt.subplots(2, 2)
+    axes[0][0].pie(sizes, explode=explode, colors=colors,
+                   shadow=True, startangle=90,
+                   wedgeprops={'linewidth': 0})
+
+    axes[0][1].pie(sizes, explode=explode, colors=colors,
+                   shadow=False, startangle=90,
+                   wedgeprops={'linewidth': 0})
+
+    axes[1][0].pie(sizes, explode=explode, colors=colors,
+                   shadow={'ox': -0.05, 'oy': -0.05, 'shade': 0.9, 'edgecolor': 'none'},
+                   startangle=90, wedgeprops={'linewidth': 0})
+
+    axes[1][1].pie(sizes, explode=explode, colors=colors,
+                   shadow={'ox': 0.05, 'linewidth': 2, 'shade': 0.2},
+                   startangle=90, wedgeprops={'linewidth': 0})
+
+
 def test_pie_textprops():
     data = [23, 34, 45]
     labels = ["Long name 1", "Long name 2", "Long name 3"]

lib/matplotlib/tests/baseline_images/test_axes/pie_shadow.png

@@ -196,8 +196,10 @@ def test_alpha_rcparam():
         leg.legendPatch.set_facecolor([1, 0, 0, 0.5])
 
 
-@image_comparison(['fancy'], remove_text=True)
+@image_comparison(['fancy'], remove_text=True, tol=0.05)
 def test_fancy():
+    # Tolerance caused by changing default shadow "shade" from 0.3 to 1 - 0.7 =
+    # 0.30000000000000004
     # using subplot triggers some offsetbox functionality untested elsewhere
     plt.subplot(121)
     plt.plot([5] * 10, 'o--', label='XX')