matplotlib · tito21 · Aug 9, 2024 · Aug 11, 2024
diff --git a/lib/matplotlib/tests/test_widgets.py b/lib/matplotlib/tests/test_widgets.py
@@ -1478,6 +1478,18 @@ def test_polygon_selector(draw_bounding_box):
     ]
     check_selector(event_sequence, expected_result, 2)
 
+    # Complete the polygon and add new vertex
+    expected_result = [(75, 75), (175, 75), (125, 180), (75, 175)]
+    event_sequence = [
+        *polygon_place_vertex(75, 75),
+        *polygon_place_vertex(175, 75),
+        *polygon_place_vertex(75, 175),
+        *polygon_place_vertex(75, 75),
+        ('press', dict(xdata=125, ydata=180)),
+        ('release', dict(xdata=125, ydata=180)),
+        ]
+    check_selector(event_sequence, expected_result, 2)
+
     # Try to move a vertex and move all before placing any vertices.
     expected_result = [(50, 50), (150, 50), (50, 150)]
     event_sequence = [

diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
@@ -1,3 +1,3 @@
 """
 GUI neutral widgets
 ===================
@@ -3723,14 +3723,32 @@
         self.update()
 
 
+def _dist_to_line(p1, p2, p3):
+    """
+    Calculates the distance of the line connecting the points p1 and p2 to point p3
+    """
+
+    def dist_sqr(p, q):
+        return (q[0] - p[0]) ** 2 + (q[1] - p[1]) ** 2
+
+    dist = dist_sqr(p1, p2)
+    if dist == 0:
+        raise ValueError("p1 and p2 are coincidental, there is no line")
+    u = ((p3[0] - p1[0]) * (p2[0] - p1[0]) + (p3[1] - p1[1]) * (p2[1] - p1[1])) / dist
+    intersection = p1[0] + u * (p2[0] - p1[0]), p1[1] + u * (p2[1] - p1[1])
+
+    return dist_sqr(intersection, p3) ** 0.5, u
+
+
 class PolygonSelector(_SelectorWidget):
     """
     Select a polygon region of an Axes.
 
     Place vertices with each mouse click, and make the selection by completing
     the polygon (clicking on the first vertex). Once drawn individual vertices
     can be moved by clicking and dragging with the left mouse button, or
-    removed by clicking the right mouse button.
+    removed by clicking the right mouse button. Also new vertices can be
+    added by left clicking.
 
     In addition, the following modifier keys can be used:
 
@@ -3890,6 +3908,8 @@
         if self._old_box_extents == self._box.extents:
             return
 
+        self._box.add_state("move")
+
         # Create transform from old box to new box
         x1, y1, w1, h1 = self._box._rect_bbox
         old_bbox = self._get_bbox()
@@ -3950,6 +3970,24 @@
                 self._draw_polygon()
             self._active_handle_idx = -1
 
+        elif (self._selection_completed
+              and "move_all"
+              not in self._state
+              and "move_vertex" not in self._state
+              and (self._box is None or "move" not in self._box._state)):
+            if event.button == 1:
+                p3 = self._get_data_coords(event)
+                min_dist = np.inf
+                index = None
+                for i, (p1, p2) in enumerate(zip(self._xys[:-1], self._xys[1:])):
+                    dist, u = _dist_to_line(p1, p2, p3)
+                    if 1 > u > 0:
+                        if min_dist > dist:
+                            min_dist = dist
+                            index = i
+                self._xys.insert(index + 1, p3)
+                self._draw_polygon()
+
         # Complete the polygon.
         elif len(self._xys) > 3 and self._xys[-1] == self._xys[0]:
             self._selection_completed = True