using (Graphics g = this.CreateGraphics())
      {
            g.DrawLine(Pens.Blue, new Point(10, 10), new Point(100, 100));
      }

     using (Graphics g = this.panel1.CreateGraphics())
     {
            g.DrawLine(Pens.Blue, new Point(10, 10), new Point(100, 100));
     }

      using (Graphics g = this.CreateGraphics())
      {
             g.Clear(this.BackColor);
      }