نکته شماره 18 :

 

private void Form1_Load(object sender, EventArgs e)
{
this.Height = 350;
this.Width = 350;
System.Drawing.Drawing2D.GraphicsPath path = new System.Drawing.Drawing2D.GraphicsPath();
path.AddEllipse(0, 0, 300, 300);
this.Region = new Region(path);
this.Show();
}