//helper class for generate arc
        //
        public static void GenerateArcNew(List <Vector> output, double cx,
                                          double cy,
                                          Vector2 startDelta,
                                          double sweepAngleRad)
        {
            //TODO: review here ***
            int    nsteps   = 4;
            double eachStep = AggMath.rad2deg(sweepAngleRad) / nsteps;
            double angle    = 0;

            for (int i = 0; i < nsteps; ++i)
            {
                Vector2 newPerpend = startDelta.RotateInDegree(angle);
                Vector2 newpos     = new Vector2(cx + newPerpend.x, cy + newPerpend.y);
                output.Add(new Vector(newpos.x, newpos.y));
                angle += eachStep;
            }
        }