添加Paint事件，接著加入下列代碼

        //將頭像設置成圓角
        private void avatar_Paint(object sender, PaintEventArgs e)
        {
            
            GraphicsPath gp = new GraphicsPath();
            gp.AddEllipse(avatar.ClientRectangle);
            Region region = new Region(gp);
            avatar.Region 
 
= region;
            gp.Dispose();
            region.Dispose();
        }

將投向設置成圓形