void panelLine_Paint(object sender, PaintEventArgs e)
{
Panel p = sender as Panel;
e.Graphics.DrawLine(Pens.Black, new Point(0, 0), new Point(0, p.Height / 2));
e.Graphics.DrawLine(Pens.Black, new Point(p.Width-1, 0), new Point(p.Width-1, p.Height / 2));
e.Graphics.DrawLine(Pens.Black, new Point(0, p.Height/2), new Point(p.Width, p.Height / 2));
e.Graphics.DrawLine(Pens.Black, new Point(p.Width / 2, p.Height / 2), new Point(p.Width / 2, p.Height));
}