刚接触c#，这个画线是怎么回事？？？

private void richTextBox1_TextChanged(object sender, EventArgs e)
        {
            int i;
            int bx,by,ex,ey;            this.richTextBox1.ScrollToCaret();
            Graphics g = this.richTextBox1.CreateGraphics();
            Brush b = new SolidBrush(Color.Red);
            Pen p = new Pen(b);            bx=40;
            by=40;
            ex=bx+80;
            ey=by;            for (i = 1; i < 10; i++)
            {
                if(i%2==0)
                {
                    g.DrawLine(p, bx, by, ex, ey);
                    bx = ex;
                    by = ey - 40;
                    ex = bx + 80;
                    ey = by;
                }
                else
                {
                    g.DrawLine(p, bx, by, ex, ey);
                    bx = ex;
                    by = ey + 40;
                    ex = bx + 80;
                    ey = by;
                }
            }
        }
我想画10组横线段 应该是出来了  但是显示不完我想像windows任务管理器性能那块那样“滚动”画出线段 怎么做？？？
我这个是直接在文本框里画的  不知道行不行？？？