程序代码：

        //设置控件的Region
        private void SetRegion()
        {
            if (base.Region != null)
            {
                base.Region.Dispose();
            }
            base.Region = new Region(GetPath(ClientRectangle,6));
        }
        //下面这个是圆角框，你可以把路径改为圆形
        private GraphicsPath GetPath(Rectangle rect,int radio)
        {
            GraphicsPath path = new GraphicsPath();
            path.AddArc(rect.X,rect.Y,radio,radio,180,90);
            path.AddArc(rect.Right - radio, rect.Y, radio, radio, 270, 90);
            path.AddArc(rect.Right-radio,rect.Bottom-radio,radio,radio,0,90);
            path.AddArc(rect.X, rect.Bottom - radio, radio, radio, 90, 90);
            path.CloseFigure();
            return path;
        }