New primitive: Boxes.step()

Outset a line by a given margin - negative values for insetting

boxes/__init__.py

@@ -717,6 +717,20 @@ class Boxes:
             self.ctx.line_to(length, 0)
         self.ctx.translate(*self.ctx.get_current_point())
 
+    def step(self, out):
+        """
+        Create a parallel step prependicular to the current direction
+        Positive values move to the outside of the part
+        """
+        if out > 1E-5:
+            self.corner(-90)
+            self.edge(out)
+            self.corner(90)
+        elif out < -1E-5:
+            self.corner(90)
+            self.edge(-out)
+            self.corner(-90)
+
     def curveTo(self, x1, y1, x2, y2, x3, y3):
         """control point 1, control point 2, end point
 

boxes/edges.py

@@ -450,17 +450,7 @@ class CompoundEdge(BaseEdge):
         lastwidth = self.types[0].startwidth()
 
         for e, l in zip(self.types, self.lengths):
-            diff = e.startwidth() - lastwidth
+            self.step(e.startwidth() - lastwidth)
-
-            if diff > 1E-5:
-                self.boxes.corner(-90)
-                self.boxes.edge(diff)
-                self.boxes.corner(90)
-            elif diff < -1E-5:
-                self.boxes.corner(90)
-                self.boxes.edge(-diff)
-                self.boxes.corner(-90)
-
             e(l)
             lastwidth = e.endwidth()