fix meander clamp (2) (#3945)

lib/stitches/meander_fill.py

@@ -185,7 +185,9 @@ def post_process(points, shape, original_shape, fill):
         stitches = even_running_stitch(smoothed_points, fill.running_stitch_length, fill.running_stitch_tolerance)
 
     if fill.clip:
-        stitches = clamp_path_to_polygon(stitches, original_shape)
+        # the stitch path may have self intersections
+        # therefore we don't want clamp polygon to check for the distance to the start point of a segment
+        stitches = clamp_path_to_polygon(stitches, original_shape, False)
 
     if fill.bean_stitch_repeats:
         stitches = bean_stitch(stitches, fill.bean_stitch_repeats)

lib/utils/clamp_path.py

@@ -88,7 +88,7 @@ def clamp_fully_external_path(path, polygon):
     return adjust_line_end(shorter, start)
 
 
-def clamp_path_to_polygon(path, polygon):
+def clamp_path_to_polygon(path, polygon, check_distance=True):
     """Constrain a path to a Polygon.
 
     The path is expected to have at least some part inside the Polygon.
@@ -131,7 +131,10 @@ def clamp_path_to_polygon(path, polygon):
             # The second part of this or condition checks whether part of the
             # path was removed by difference() above, because it coincided
             # with part of the shape border.
-            if not was_inside and last_point_inside is not None:
+            if last_point_inside is not None and (
+                not was_inside or
+                (check_distance and last_point_inside.distance(start) > 0.01)
+            ):
                 # We traveled outside or on the border of the shape for
                 # a while.  In either case, we need to add a path along the
                 # border between the exiting and entering points.