middle of massive restructure, everything still broken

helpers.py

@@ -93,6 +93,38 @@ def random_color():
     color.set_rgb([1 - 0.5 * random() for x in range(3)])
     return color
 
+
+################################################
+
+def straight_path(start_points, end_points, alpha):
+    return (1-alpha)*start_points + alpha*end_points
+
+def path_along_arc(arc_angle):
+    """
+    If vect is vector from start to end, [vect[:,1], -vect[:,0]] is 
+    perpendicualr to vect in the left direction.
+    """
+    if arc_angle == 0:
+        return straight_path
+    def path(start_points, end_points, alpha):
+        vects = end_points - start_points
+        centers = start_points + 0.5*vects
+        if arc_angle != np.pi:
+            for i, b in [(0, -1), (1, 1)]:
+                centers[:,i] += 0.5*b*vects[:,1-i]/np.tan(arc_angle/2)
+        return centers + np.dot(
+            start_points-centers, 
+            np.transpose(rotation_about_z(alpha*arc_angle))
+        )
+    return path
+
+def clockwise_path():
+    return path_along_arc(np.pi)
+
+def counterclockwise_path():
+    return path_along_arc(-np.pi)
+
+
 ################################################
 
 def to_cammel_case(name):