added test and improve comments for third party backend support of hatchcolors arg

Author: r3kste

doc/users/next_whats_new/separated_hatchcolor.rst

@@ -78,9 +78,9 @@ to 'patch.edgecolor' with the alpha value of the collection.
 
     fig, ax = plt.subplots()
 
-    x = np.random.rand(20)
-    y = np.random.rand(20)
-    colors = ["blue", "orange", "green"]
+    x = [29, 36, 41, 25, 32, 70, 62, 58, 66, 80, 58, 68, 62, 37, 48]
+    y = [82, 76, 48, 53, 62, 70, 84, 68, 55, 75, 29, 25, 12, 17, 20]
+    colors = ['tab:blue'] * 5 + ['tab:orange'] * 5 + ['tab:green'] * 5
 
     ax.scatter(
         x,

galleries/examples/shapes_and_collections/hatchcolor_demo.py

@@ -69,7 +69,7 @@
     facecolor="none",
     edgecolor="gray",
     linewidth=2,
-    marker="s",  # Use hexagon as marker
+    marker="h",  # Use hexagon as marker
     hatch="xxx",
     hatchcolor=colors,
 )

lib/matplotlib/collections.py

@@ -423,7 +423,10 @@ def draw(self, renderer):
             # The current new API of draw_path_collection() is provisional
             # and will be changed in a future PR.
 
-            # Find whether renderer.draw_path_collection() takes hatchcolor parameter
+            # Find whether renderer.draw_path_collection() takes hatchcolor parameter.
+            # Since third-party implementations of draw_path_collection() may not be
+            # introspectable, e.g. with inspect.signature, the only way is to try and
+            # call this with the hatchcolors parameter.
             hatchcolors_arg_supported = True
             try:
                 renderer.draw_path_collection(
@@ -435,6 +438,9 @@ def draw(self, renderer):
                     "screen", hatchcolors=self.get_hatchcolor()
                 )
             except TypeError:
+                # If the renderer does not support the hatchcolors argument,
+                # it will raise a TypeError. In this case, we will
+                # iterate over all paths and draw them one by one.
                 hatchcolors_arg_supported = False
 
             if self._gapcolor is not None:
@@ -449,8 +455,6 @@ def draw(self, renderer):
                                                   self.get_transforms(), *args,
                                                   hatchcolors=self.get_hatchcolor())
                 else:
-                    # If the renderer does not support the hatchcolors argument,
-                    # iterate over the paths and draw them one by one.
                     path_ids = renderer._iter_collection_raw_paths(
                         transform.frozen(), ipaths, self.get_transforms())
                     for xo, yo, path_id, gc0, rgbFace in renderer._iter_collection(

lib/matplotlib/tests/test_collections.py

@@ -1486,3 +1486,28 @@ def test_draw_path_collection_no_hatchcolor(backend):
         facecolors, edgecolors, linewidths, linestyles,
         antialiaseds, urls, offset_position
     )
+
+
+def test_third_party_backend_hatchcolors_arg_fallback(monkeypatch):
+    fig, ax = plt.subplots()
+    canvas = fig.canvas
+    renderer = canvas.get_renderer()
+
+    # monkeypatch the `draw_path_collection` method to simulate a third-party backend
+    # that does not support the `hatchcolors` argument.
+    def mock_draw_path_collection(self, gc, master_transform, paths, all_transforms,
+                                  offsets, offset_trans, facecolors, edgecolors,
+                                  linewidths, linestyles, antialiaseds, urls,
+                                  offset_position):
+        pass
+
+    monkeypatch.setattr(renderer, 'draw_path_collection', mock_draw_path_collection)
+
+    # Create a PathCollection with hatch colors
+    from matplotlib.collections import PathCollection
+    path = mpath.Path.unit_rectangle()
+    coll = PathCollection([path], hatch='//', hatchcolor='red')
+
+    ax.add_collection(coll)
+
+    plt.draw()