class interface DRAWABLE_POLYLINE creation make -- Create. feature(s) from DRAWABLE_POLYLINE -- Position empty: BOOLEAN -- Is the polyline empty (no points)? reset -- Reset the point list representing the polyline. ensure done: empty add_point (pt: POINT) -- Add a new point at the end of the polyline. require valid_point: pt /= Void ensure ok: not empty invariant valid_position: line /= Void; end of DRAWABLE_POLYLINE