c#拖动长图片

//////////////鼠标拖动图片/////////////
        /////////////定义图片位置，全局变量////////////
        Point M_pot_p = new Point();//原始位置
        int M_int_mx = 0, M_int_my = 0;//下次能继续
        int M_int_maxX, M_int_maxY;//加快读取用   
      private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            Bitmap tmpbmp = (Bitmap)this.pictureBox1.Image;
            M_pot_p = e.Location;
            M_int_maxX = pictureBox1.Width - tmpbmp.Width;
            M_int_maxY = pictureBox1.Height - tmpbmp.Height;
            Cursor = Cursors.SizeAll;
        }
        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)//当按左键的时候
            {
                //算差值
                Bitmap tmpbmp = (Bitmap)this.pictureBox1.Image;
                M_int_mx = M_int_mx - M_pot_p.X + e.X;
                M_int_my = M_int_my - M_pot_p.Y + e.Y;
                //锁定范围
                M_int_mx = Math.Min(0, Math.Max(M_int_maxX, M_int_mx));
                M_int_my = Math.Min(0, Math.Max(M_int_maxY, M_int_my));
                Graphics g = pictureBox1.CreateGraphics();
                g.DrawImage(tmpbmp, new Rectangle(0, 0, pictureBox1.Width, pictureBox1.Height), new Rectangle(-M_int_mx, -M_int_my, pictureBox1.Width, pictureBox1.Height), GraphicsUnit.Pixel);
                M_pot_p = e.Location;
            }
            else
            {
                Cursor = Cursors.Default;
            }
        }