winform 不规则显示

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using System.Drawing.Drawing2D;

using System.Threading;



namespace WindowsApplication194

{

    public partial class Form1 : Form, IMessageFilter

    {

        Button B = new Button();

        PictureBox PB = new PictureBox();

        Form F = new Form();

        GraphicsPath GP = new GraphicsPath();



        public Form1()

        {

            InitializeComponent();



            Application.AddMessageFilter(this);



            B.Parent = this;



            GP.AddEllipse(0, 0, 80, 40);

            GP.AddEllipse(20, 45, 40, 15);

            GP.AddEllipse(25, 70, 20, 10);



            F.Opacity = 0;

            F.FormBorderStyle = FormBorderStyle.None;

            F.Size = new Size(100, 100);

            F.Region = new Region(GP);

            F.TopMost = true;

            DoDraw(String.Empty);  

            F.Show();



            PB.Parent = F;

            PB.Dock = DockStyle.Fill;

        }



        public bool PreFilterMessage(ref Message m)

        {

            int WM_MOUSEMOVE = 0x200;



            if (m.Msg == WM_MOUSEMOVE)

            {

                if (B.Bounds.Contains(this.PointToClient(Control.MousePosition)))

                {

                    F.Location = Point.Add(Control.MousePosition, new Size(-25, -F.Height));

                    F.Show();

                    new Thread(new ParameterizedThreadStart(ShowFormThread)).Start("ABC");

                    this.Focus();

                }

                else

                {

                    F.Opacity = 0;

                    F.Hide();

                }

            }

            return false;

        }



        void ShowFormThread(Object Obj)

        {

            try

            {

                String Text = Obj.ToString();

                int StartTick = Environment.TickCount;



                this.Invoke(new Draw(DoDraw), new Object[] { Text });

                

                while ((double)this.Invoke(new GetOpacity(DoGetOpacity)) < 0.8)

                    if (Environment.TickCount - StartTick > 200)

                    {

                        this.Invoke(new IncOpacity(DoIncOpacity));



                        StartTick = Environment.TickCount;

                    }

            }

            catch

            {

                // 忽略程序退出的异常

            }

        }



        delegate double GetOpacity();

        delegate void IncOpacity();

        delegate void Draw(String Text);



        double DoGetOpacity()

        {

            return F.Opacity;

        }



        void DoIncOpacity()

        {

            F.Opacity += 0.1;

        }



        void DoDraw(String Text)

        {

            Bitmap Bmp = new Bitmap(PB.ClientRectangle.Width, PB.ClientRectangle.Height);



            using (Graphics G = Graphics.FromImage(Bmp))

            {

                SizeF SF = G.MeasureString(Text, F.Font);



                G.Clear(Color.Yellow);

                G.DrawPath(Pens.Black, GP);

                G.DrawString(Text, F.Font, Brushes.Black, (80 - SF.Width) / 2, 10);

            }

            PB.Image = Bmp;

        }

    }

}