public override VoltShape PrepareShape(VoltWorld world)
 {
     Vector2[] vertices = new Vector2[this.points.Length];
     for (int i = 0; i < this.points.Length; i++)
       vertices[i] = this.points[i].position;
     this.shape = world.CreatePolygonWorldSpace(
       vertices,
       this.density);
     return this.shape;
 }