c# UpdateLayeredWindow异形窗口

　　　　 #region UpdateLayeredWindow

        #region 重写窗体的 CreateParams 属性
        protected override CreateParams CreateParams
        {
            get
            {
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= 0x00080000;  //  WS_EX_LAYERED 扩展样式
                //无边框任务栏窗口最小化
                const int WS_MINIMIZEBOX = 0x00020000;  // Winuser.h中定义
                //CreateParams cp = base.CreateParams;
                cp.Style = cp.Style | WS_MINIMIZEBOX;   // 允许最小化操作
                return cp;
            }
        }
        #endregion

        #region API调用
        public void SetBits(Bitmap bitmap)//调用UpdateLayeredWindow（）方法。this.BackgroundImage为你事先准备的带透明图片。
        {
            //if (!haveHandle) return;

            if (!Bitmap.IsCanonicalPixelFormat(bitmap.PixelFormat) || !Bitmap.IsAlphaPixelFormat(bitmap.PixelFormat))
                throw new ApplicationException("图片必须是32位带Alhpa通道的图片。");

            IntPtr oldBits = IntPtr.Zero;
            IntPtr screenDC = Win32.GetDC(IntPtr.Zero);
            IntPtr hBitmap = IntPtr.Zero;
            IntPtr memDc = Win32.CreateCompatibleDC(screenDC);

            try
            {
                Win32.Point topLoc = new Win32.Point(Left, Top);
                Win32.Size bitMapSize = new Win32.Size(bitmap.Width, bitmap.Height);
                Win32.BLENDFUNCTION blendFunc = new Win32.BLENDFUNCTION();
                Win32.Point srcLoc = new Win32.Point(0, 0);

                hBitmap = bitmap.GetHbitmap(Color.FromArgb(0));
                oldBits = Win32.SelectObject(memDc, hBitmap);

                blendFunc.BlendOp = Win32.AC_SRC_OVER;
                blendFunc.SourceConstantAlpha = 255;
                blendFunc.AlphaFormat = Win32.AC_SRC_ALPHA;
                blendFunc.BlendFlags = 0;

                Win32.UpdateLayeredWindow(Handle, screenDC, ref topLoc, ref bitMapSize, memDc, ref srcLoc, 0, ref blendFunc, Win32.ULW_ALPHA);
            }
            finally
            {
                if (hBitmap != IntPtr.Zero)
                {
                    Win32.SelectObject(memDc, oldBits);
                    Win32.DeleteObject(hBitmap);
                }
                Win32.ReleaseDC(IntPtr.Zero, screenDC);
                Win32.DeleteDC(memDc);
            }
        }
        #endregion

        #endregion

        public MainForm()
        {
            InitializeComponent();
            Bitmap bg = new Bitmap(this.Width, this.Height);
            Graphics g = Graphics.FromImage(bg);
            g.DrawImage(img, x, y, img.Width, img.Height);
            g.Dispose();
            SetBits(bg);
        }