Merge pull request #24103 from meeseeksmachine/auto-backport-of-pr-23…

…684-on-v3.6.x

Backport PR #23684 on branch v3.6.x (Fix rectangle and hatches for colorbar)

lib/matplotlib/colorbar.py

@@ -606,10 +606,13 @@ def _update_dividers(self):
         self.dividers.set_segments(segments)
 
     def _add_solids_patches(self, X, Y, C, mappable):
-        hatches = mappable.hatches * len(C)  # Have enough hatches.
+        hatches = mappable.hatches * (len(C) + 1)  # Have enough hatches.
+        if self._extend_lower():
+            # remove first hatch that goes into the extend patch
+            hatches = hatches[1:]
         patches = []
         for i in range(len(X) - 1):
-            xy = np.array([[X[i, 0], Y[i, 0]],
+            xy = np.array([[X[i, 0], Y[i, 1]],
                            [X[i, 1], Y[i, 0]],
                            [X[i + 1, 1], Y[i + 1, 0]],
                            [X[i + 1, 0], Y[i + 1, 1]]])
@@ -661,9 +664,9 @@ def _do_extends(self, ax=None):
         mappable = getattr(self, 'mappable', None)
         if (isinstance(mappable, contour.ContourSet)
                 and any(hatch is not None for hatch in mappable.hatches)):
-            hatches = mappable.hatches
+            hatches = mappable.hatches * (len(self._y) + 1)
         else:
-            hatches = [None]
+            hatches = [None] * (len(self._y) + 1)
 
         if self._extend_lower():
             if not self.extendrect:
@@ -687,6 +690,8 @@ def _do_extends(self, ax=None):
                 zorder=np.nextafter(self.ax.patch.zorder, -np.inf))
             self.ax.add_patch(patch)
             self._extend_patches.append(patch)
+            # remove first hatch that goes into the extend patch
+            hatches = hatches[1:]
         if self._extend_upper():
             if not self.extendrect:
                 # triangle
@@ -699,10 +704,12 @@ def _do_extends(self, ax=None):
             # add the patch
             val = 0 if self._long_axis().get_inverted() else -1
             color = self.cmap(self.norm(self._values[val]))
+            hatch_idx = len(self._y) - 1
             patch = mpatches.PathPatch(
                 mpath.Path(xy), facecolor=color, alpha=self.alpha,
                 linewidth=0, antialiased=False,
-                transform=self.ax.transAxes, hatch=hatches[-1], clip_on=False,
+                transform=self.ax.transAxes, hatch=hatches[hatch_idx],
+                clip_on=False,
                 # Place it right behind the standard patches, which is
                 # needed if we updated the extends
                 zorder=np.nextafter(self.ax.patch.zorder, -np.inf))

lib/matplotlib/tests/test_colorbar.py

@@ -998,6 +998,36 @@ def test_colorbar_extend_drawedges():
             np.testing.assert_array_equal(cbar.dividers.get_segments(), res)
 
 
+@image_comparison(['contourf_extend_patches.png'], remove_text=True,
+                  style='mpl20')
+def test_colorbar_contourf_extend_patches():
+    params = [
+        ('both', 5, ['\\', '//']),
+        ('min', 7, ['+']),
+        ('max', 2, ['|', '-', '/', '\\', '//']),
+        ('neither', 10, ['//', '\\', '||']),
+    ]
+
+    plt.rcParams['axes.linewidth'] = 2
+
+    fig = plt.figure(figsize=(10, 4))
+    subfigs = fig.subfigures(1, 2)
+    fig.subplots_adjust(left=0.05, bottom=0.05, right=0.95, top=0.95)
+
+    x = np.linspace(-2, 3, 50)
+    y = np.linspace(-2, 3, 30)
+    z = np.cos(x[np.newaxis, :]) + np.sin(y[:, np.newaxis])
+
+    cmap = mpl.colormaps["viridis"]
+    for orientation, subfig in zip(['horizontal', 'vertical'], subfigs):
+        axs = subfig.subplots(2, 2).ravel()
+        for ax, (extend, levels, hatches) in zip(axs, params):
+            cs = ax.contourf(x, y, z, levels, hatches=hatches,
+                             cmap=cmap, extend=extend)
+            subfig.colorbar(cs, ax=ax, orientation=orientation, fraction=0.4,
+                            extendfrac=0.2, aspect=5)
+
+
 def test_negative_boundarynorm():
     fig, ax = plt.subplots(figsize=(1, 3))
     cmap = mpl.colormaps["viridis"]