Fix dash offset bug in Patch (matplotlib#23412)

* Add passed offset in draw method of Patch

* Add entry to whats new about dash offset

* Remove trailing spaces

* Add test for dash offset in Patch

* Refactor test_dash_offset_patch_draw

* Correct mention of code object

* Fix indentation in draw method of Patch

Author: AnnaMastori

doc/users/next_whats_new/fix_dash_offset_Patch.rst

@@ -0,0 +1,5 @@
+Fix the dash offset of the Patch class
+--------------------------------------
+Traditionally, when setting the linestyle on a `.Patch` object using a dash tuple the
+offset was ignored. Now the offset is passed to the draw method of Patch as expected
+and it can be used as it is used with Line2D objects.

lib/matplotlib/patches.py

@@ -586,9 +586,8 @@ def draw(self, renderer):
         # docstring inherited
         if not self.get_visible():
             return
-        # Patch has traditionally ignored the dashoffset.
-        with cbook._setattr_cm(
-                 self, _dash_pattern=(0, self._dash_pattern[1])), \
+
+        with cbook._setattr_cm(self, _dash_pattern=(self._dash_pattern)), \
              self._bind_draw_path_function(renderer) as draw_path:
             path = self.get_path()
             transform = self.get_transform()

lib/matplotlib/tests/test_patches.py

@@ -149,6 +149,40 @@ def test_rotate_rect_draw(fig_test, fig_ref):
     assert rect_test.get_angle() == angle
 
 
+@check_figures_equal(extensions=['png'])
+def test_dash_offset_patch_draw(fig_test, fig_ref):
+    ax_test = fig_test.add_subplot()
+    ax_ref = fig_ref.add_subplot()
+
+    loc = (0.1, 0.1)
+    width, height = (0.8, 0.8)
+    rect_ref = Rectangle(loc, width, height, linewidth=3, edgecolor='b',
+                                                linestyle=(0, [6, 6]))
+    # fill the line gaps using a linestyle (0, [0, 6, 6, 0]), which is
+    # equivalent to (6, [6, 6]) but has 0 dash offset
+    rect_ref2 = Rectangle(loc, width, height, linewidth=3, edgecolor='r',
+                                            linestyle=(0, [0, 6, 6, 0]))
+    assert rect_ref.get_linestyle() == (0, [6, 6])
+    assert rect_ref2.get_linestyle() == (0, [0, 6, 6, 0])
+
+    ax_ref.add_patch(rect_ref)
+    ax_ref.add_patch(rect_ref2)
+
+    # Check that the dash offset of the rect is the same if we pass it in the
+    # init method and if we create two rects with appropriate onoff sequence
+    # of linestyle.
+
+    rect_test = Rectangle(loc, width, height, linewidth=3, edgecolor='b',
+                                                    linestyle=(0, [6, 6]))
+    rect_test2 = Rectangle(loc, width, height, linewidth=3, edgecolor='r',
+                                                    linestyle=(6, [6, 6]))
+    assert rect_test.get_linestyle() == (0, [6, 6])
+    assert rect_test2.get_linestyle() == (6, [6, 6])
+
+    ax_test.add_patch(rect_test)
+    ax_test.add_patch(rect_test2)
+
+
 def test_negative_rect():
     # These two rectangles have the same vertices, but starting from a
     # different point.  (We also drop the last vertex, which is a duplicate.)