fix STOP handling

Apparently STOP codes (a.k.a. color changes) should be by themselves, not
attached to another stitch.  To add a STOP code at a given stitch, we should
clone the stitch and then set the STOP command on the new stitch.

lib/stitch_plan/stitch.py

@@ -13,3 +13,6 @@ class Stitch(Point):
 
     def __repr__(self):
         return "Stitch(%s, %s, %s, %s, %s, %s, %s)" % (self.x, self.y, self.color, "JUMP" if self.jump else " ", "TRIM" if self.trim else " ", "STOP" if self.stop else " ", "NO TIES" if self.no_ties else " ")
+
+    def copy(self):
+        return Stitch(self.x, self.y, self.color, self.jump, self.stop, self.trim, self.no_ties)

lib/stitch_plan/stitch_plan.py

@@ -39,8 +39,12 @@ def patches_to_stitch_plan(patches, collapse_len=3.0 * PIXELS_PER_MM):
                     color_block.add_stitch(patch.stitches[0].x, patch.stitches[0].y, jump=True)
 
         else:
-            # add a color change
-            color_block.add_stitch(color_block.last_stitch.x, color_block.last_stitch.y, stop=True)
+            # add a color change (only if the last stitch wasn't a "STOP after")
+            if not color_block.last_stitch.stop:
+                stitch = color_block.last_stitch.copy()
+                stitch.stop = True
+                color_block.add_stitch(stitch)
+
             color_block = stitch_plan.new_color_block()
             color_block.color = patch.color
 

lib/stitch_plan/stop.py

@@ -17,11 +17,18 @@ def process_stop(color_block):
     """
 
     if len(color_block.stitches) >= 3:
-        color_block.stitches[-3].stop = True
+        # make a copy of the stitch and turn it into a STOP code
+        stitch = color_block.stitches[-3].copy()
+        stitch.stop = True
+
+        # insert it after the stitch
+        color_block.stitches.insert(-2, stitch)
 
     # and also add a color change on this stitch, completing the C00
     # block:
 
-    color_block.stitches[-1].stop = True
+    stitch = color_block.stitches[-1].copy()
+    stitch.stop = True
+    color_block.add_stitch(stitch)
 
     # reference for the above: https://github.com/lexelby/inkstitch/pull/29#issuecomment-359175447