private void panel1_MouseDown1(object sender, MouseEventArgs e)
        {
            this.tmpX = e.X;
            this.tmpY = e.Y;
            this.panel1.MouseDown += new System.Windows.Forms.MouseEventHandler(this.panel1_MouseDown2);
 
        }
private void panel1_MouseDown2(object sender, MouseEventArgs e)
        {
            System.Drawing.Graphics g = this.panel1.CreateGraphics();
            System.Drawing.Pen newPen = new System.Drawing.Pen(Color.Red, 10);
            g.DrawLine(newPen,new Point(this.tmpX, this.tmpY), new Point( e.X, e.Y));
            this.panel1.MouseDown += new System.Windows.Forms.MouseEventHandler(this.panel1_MouseDown1);
        }

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