usercontrol 画圆角

   protected override void OnResize(EventArgs e)
    {
        this.Region = null;
        SetWindowR();

    }

    private void SetWindowR()
    {
        System.Drawing.Drawing2D.GraphicsPath gPath = new System.Drawing.Drawing2D.GraphicsPath();
        Rectangle rect = new Rectangle(0, 5, this.Width, this.Height - 5);
        gPath = GetRoundedRP(rect, 390); //后面的30是圆的角度，数值越大圆角度越大
        this.Region = new Region(gPath);
    }

    private System.Drawing.Drawing2D.GraphicsPath GetRoundedRP(Rectangle rect, int a)
    {
        int diameter = a;
        Rectangle arcRect = new Rectangle(rect.Location, new Size(diameter, diameter));
        System.Drawing.Drawing2D.GraphicsPath gp = new System.Drawing.Drawing2D.GraphicsPath();
        // 左上角
        //gp.AddArc(arcRect, 180, 90);
        gp.AddArc(0, 0, 70, 70, 180, 90);
        // 右上角
        arcRect.X = rect.Right - diameter;
        gp.AddArc(arcRect, 270, 90);
        // 右下角
        arcRect.Y = rect.Bottom;
        gp.AddArc(this.Width - 50, this.Height - 50, 50, 50, 0, 90);
        //gp.AddArc(arcRect, 0, 90);
        // 左下角
        arcRect.X = rect.Left;
        gp.AddArc(arcRect, 90, 90);
        gp.CloseFigure();
        return gp;
    }