视频叠加圆后的居中问题

上个问题
http://topic.csdn.net/u/20091027/00/59cf59f7-bd2d-44bd-8aee-942732f62ba6.html根据反馈问题的代码进行相应修改，代码如下
//// <summary>
        /// 绘制实心圆
        /// </summary>
        /// <param name="Border">边框大小</param>
        private void FillEllipse(int Border)
        {
            GraphicsPath GP = new GraphicsPath();
            GP.AddEllipse(new Rectangle(0, 0, Border, Border));            Bitmap Bmp = new Bitmap(Border, Border);
            Brush br = new SolidBrush(Properties.Settings.Default.CircleColor);
            using (Graphics G = Graphics.FromImage(Bmp))
                G.FillEllipse(br, new Rectangle(0, 0, Border, Border));            Panel P = new Panel();
            P.Name = "P";
            P.BorderStyle = BorderStyle.Fixed3D;
            P.Parent = this;
           
            if (frmPB == null) { frmPB = new Form(); }
             
            frmPB.Name = "frmPB";
            frmPB.Size = new Size(Border, Border);
            frmPB.FormBorderStyle = FormBorderStyle.None;
            frmPB.BackgroundImage = Bmp;
            frmPB.Opacity = 0.3;
            frmPB.ShowIcon = false;
            frmPB.ShowInTaskbar = false;
            frmPB.Region = new Region(GP);
            
            if (!ShowOnece || frmPB == null) 
            {
                frmPB.Show(P);
                ShowOnece = true;
            }
            
           
            this.LocationChanged += new EventHandler(frmMain_LocationChanged);        }        void frmMain_LocationChanged(object sender, EventArgs e)
        {
            try
            {
                
                Panel P = (Panel)this.Controls.Find("P", true)[0];                if (P == null) return;
                //Application.OpenForms["F"].Location = P.PointToScreen(new Point(0, 0));                Application.OpenForms["frmPB"].Location = P.PointToScreen(
                    new Point(panelVideo.Top + (panelVideo.Width - P.Width) / 2,
                        panelVideo.Left + (panelVideo.Height - P.Height) / 2));
            }
            catch (Exception)
            {
                
               // throw;
            }
        }
有两个问题：
1：P.PointToScreen(）是以窗体的左上角XY为基准，需要以圆为中心进行调整
2、代码运行后首先圆不是居中的，窗体缩小后再放大就居中了，不知道是什么有因造成的