Graphics绘图，画矩形，长方形（入门级）

绘图，画矩形，长方形// 创建GDI
            Graphics g = this.panel1.CreateGraphics();
            //创建两个点
            Point n1 = new Point(20, 20);
            Point n2 = new Point(100, 100);

            //创建画笔
            Pen p = new Pen(Brushes.Black, 2);
            p.EndCap = LineCap.ArrowAnchor;//定义线尾的样式为箭头
            g.DrawLine(p, n1, n2);