Winform 圆角

//Paint circle.
        public void SetWindowRegion()
        {
            System.Drawing.Drawing2D.GraphicsPath FormPath;
            FormPath = new System.Drawing.Drawing2D.GraphicsPath();
            Rectangle rect = new Rectangle(0, 22, this.Width, this.Height - 22);//this.Left-10,this.Top-10,this.Width-10,this.Height-10);                
            FormPath = GetRoundedRectPath(rect, 30);
            this.Region = new Region(FormPath);
        }

        private GraphicsPath GetRoundedRectPath(Rectangle rect, int radius)
        {
            int diameter = radius;
            Rectangle arcRect = new Rectangle(rect.Location, new Size(diameter, diameter));
            GraphicsPath path = new GraphicsPath();
            //   左上角  
            path.AddArc(arcRect, 180, 90);
            //   右上角  
            arcRect.X = rect.Right - diameter;
            path.AddArc(arcRect, 270, 90);
            //   右下角  
            arcRect.Y = rect.Bottom - diameter;
            path.AddArc(arcRect, 0, 90);
            //   左下角  
            arcRect.X = rect.Left;
            path.AddArc(arcRect, 90, 90);
            path.CloseFigure();
            return path;
        }

        protected override void OnResize(System.EventArgs e)
        {
            this.Region = null;
            SetWindowRegion();
        }