added comment

Tillsten · Tillsten · commit 7bd9d3cb62d7 · 2020-04-30T10:13:31.000+02:00
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -229,6 +229,9 @@ def draw_path_collection(self, gc, master_transform, paths, all_transforms,
                 antialiaseds, urls, offset_position):
             path, transform = path_id
             if xo != 0 or yo != 0:
+                # The transformation can be used by multiple paths. Since
+                # translate is a inplace operation, we need to copy the
+                # transformation by .frozen().                
                 transform = transform.frozen()
                 transform.translate(xo, yo)
             self.draw_path(gc0, path, transform, rgbFace)
