网线帘幕动画

        /*
         *      黄
         *   蓝    红
         *      绿
         */
        private void btnStart_Click(object sender, EventArgs e)
        {
            //pic是 PictureBox : Size=new Size(256, 256);
            Graphics g = pic.CreateGraphics();
            g.Clear(Color.White);
            Pen blue = new Pen(Color.Blue);
            Pen red = new Pen(Color.Red);
            Pen yellow = new Pen(Color.Yellow);
            Pen green = new Pen(Color.Green);
            //绘制四角网线
            int y = 255;
            int x = 0;
            for (x = 0; x < 256; x += 5)
            {
                ///每条线的两点沿着正方形的边顺时针走
                g.DrawLine(yellow, x, 0, 255, x);///黄色第一点在正方形的顶边，第二点在正方形右边
                g.DrawLine(red, 255, x, y, 255);//红色第一点在正方形的右边，第二点在正方形底边
                g.DrawLine(green, y, 255, 0, y);//绿色第一点在正方形的底边，第二点在正方形左边
                g.DrawLine(blue, 0, y, x, 0);//蓝色第一点在正方形的左边，第二点在正方形顶边
                y -= 5;

                Thread.Sleep(50);
            }
            //四边透明度依次递减
            for (y = 0; y < 256; y++)
            {
                using (Pen pen = new Pen(Color.FromArgb(y, Color.Yellow)))
                    g.DrawLine(pen, 0, y, 255, y);//两点向下 y增大
                using (Pen pen = new Pen(Color.FromArgb(y, Color.Red)))
                    g.DrawLine(pen, x, 0, x, 255);//两点向左 x减小
                using (Pen pen = new Pen(Color.FromArgb(y, Color.Green)))
                    g.DrawLine(pen, 0, x, 255, x);
                using (Pen pen = new Pen(Color.FromArgb(y, Color.Blue)))
                    g.DrawLine(pen, y, 0, y, 255);
                x--;
                if (y > 128)
                    break;
                Thread.Sleep(10);
            }
            blue.Dispose();
            red.Dispose();
            green.Dispose();
            yellow.Dispose();
        }