public void drawTriangle(PointF a, PointF b, PointF c, int iter)
        {
            if (iter == 0)
                return;
            PointF m = new PointF();
            PointF ab = new PointF();
            PointF ac = new PointF();
            ab.X = b.X - a.X;
            ab.Y = b.Y - a.Y;
            ac.X = c.X - a.X;
            ac.Y = c.Y - a.Y;
            m.X = a.X + (ab.X + ac.X) / 3;
            m.Y = a.Y + (ab.Y + ac.Y) / 3;
            graph.DrawLine(pen, a.X, a.Y, m.X, m.Y);
            graph.DrawLine(pen, b.X, b.Y, m.X, m.Y);
            graph.DrawLine(pen, c.X, c.Y, m.X, m.Y);
            drawTriangle(a, b, m, iter - 1);
            drawTriangle(b, c, m, iter - 1);
            drawTriangle(a, c, m, iter - 1);
        }