re-sort the polygons only in the last layer (to avoid breaking-away pieces)

git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@606 bbaffbd6-741e-11dd-a85d-61de82d9cad9

src/pycam/PathGenerators/EngraveCutter.py

@@ -67,25 +67,6 @@ class EngraveCutter:
                 draw_callback)
 
         line_groups = self.contour_model.get_polygons()
-        # Sort the polygons according to their directions (first inside, then
-        # outside. Smaller polygons are processed first.
-        # This reduces the problem of break-away pieces.
-        def polygon_priority(poly1, poly2):
-            """ polygon priority comparison: first holes, then outlines
-            (sorted by ascending area size)
-            TODO: ordering according to the locations and groups of polygons
-            would be even better.
-            """
-            area1 = poly1.get_area()
-            area2 = poly2.get_area()
-            if (area1 < 0) and (area2 > 0):
-                return -1
-            elif (area2 < 0) and (area1 > 0):
-                return 1
-            else:
-                return cmp(abs(area1), abs(area2))
-        line_groups.sort(cmp=polygon_priority)
-
         # push slices for all layers above ground
         for z in z_steps[:-1]:
             # update the progress bar and check, if we should cancel the process
@@ -120,6 +101,27 @@ class EngraveCutter:
             draw_callback(text="Engrave: processing layer %d/%d" \
                     % (current_layer + 1, num_of_layers))
 
+        # Sort the polygons according to their directions (first inside, then
+        # outside.
+        # This reduces the problem of break-away pieces.
+        # We do the sorting just before the final layer (breakage does not
+        # happen before).
+        def polygon_priority(poly1, poly2):
+            """ polygon priority comparison: first holes, then outlines
+            (sorted by ascending area size)
+            TODO: ordering according to the locations and groups of polygons
+            would be even better.
+            """
+            area1 = poly1.get_area()
+            area2 = poly2.get_area()
+            if (area1 < 0) and (area2 > 0):
+                return -1
+            elif (area2 < 0) and (area1 > 0):
+                return 1
+            else:
+                return 0
+        line_groups.sort(cmp=polygon_priority)
+
         # process the final layer with a drop cutter
         for line_group in self.contour_model.get_polygons():
             self.pa_drop.new_direction(0)