protected  override CreateParams CreateParams 
      { 
       get 
         { 
         CreateParams cp =  base .CreateParams; 
         cp.ExStyle |=  0x00080000 ; // WS_EX_LAYERED 扩展样式 
         return cp; 
       } 
     } 

public  void SetBitmap(Bitmap bitmap, byte opacity) 
  { 
   if (bitmap.PixelFormat != PixelFormat.Format32bppArgb) 
     throw  new ApplicationException( "位图必须是32位包含alpha 通道" ); 
 
  IntPtr screenDc = Win32.GetDC(IntPtr.Zero); 
  IntPtr memDc = Win32.CreateCompatibleDC(screenDc); 
  IntPtr hBitmap = IntPtr.Zero; 
  IntPtr oldBitmap = IntPtr.Zero; 
 
   try 
     { 
    hBitmap = bitmap.GetHbitmap(Color.FromArgb( 0 ));  // 创建GDI位图句柄，效率较低 
    oldBitmap = Win32.SelectObject(memDc, hBitmap); 
 
    Win32.Size size =  new Win32.Size(bitmap.Width, bitmap.Height); 
    Win32.Point pointSource =  new Win32.Point( 0 , 0 ); 
    Win32.Point topPos =  new Win32.Point(Left, Top); 
    Win32.BLENDFUNCTION blend =  new Win32.BLENDFUNCTION(); 
    blend.BlendOp       = Win32.AC_SRC_OVER; 
    blend.BlendFlags      =  0 ; 
    blend.SourceConstantAlpha = opacity; 
    blend.AlphaFormat     = Win32.AC_SRC_ALPHA; 
 
    Win32.UpdateLayeredWindow(Handle, screenDc, ref topPos, ref size, memDc, ref pointSource, 0 , ref blend, Win32.ULW_ALPHA); 
  } 
   finally 
     { 
    Win32.ReleaseDC(IntPtr.Zero, screenDc); 
     if (hBitmap != IntPtr.Zero) 
       { 
      Win32.SelectObject(memDc, oldBitmap); 
       
      Win32.DeleteObject(hBitmap); 
    } 
    Win32.DeleteDC(memDc); 
  } 
} 

class Win32 
  { 
   public  enum Bool 
    { 
    False =  0 , 
    True 
  } ; 
 
 
  [StructLayout(LayoutKind.Sequential)] 
   public  struct Point 
     { 
     public Int32 x; 
     public Int32 y; 
 
     public Point(Int32 x, Int32 y) 
     { this .x = x; this .y = y; } 
  } 
 
 
  [StructLayout(LayoutKind.Sequential)] 
   public  struct Size 
     { 
     public Int32 cx; 
     public Int32 cy; 
 
     public Size(Int32 cx, Int32 cy) 
      { this .cx = cx; this .cy = cy; } 
  } 
 
 
  [StructLayout(LayoutKind.Sequential, Pack =  1 )] 
   struct ARGB 
    { 
     public  byte Blue; 
     public  byte Green; 
     public  byte Red; 
     public  byte Alpha; 
  } 
 
 
  [StructLayout(LayoutKind.Sequential, Pack =  1 )] 
   public  struct BLENDFUNCTION 
     { 
     public  byte BlendOp; 
     public  byte BlendFlags; 
     public  byte SourceConstantAlpha; 
     public  byte AlphaFormat; 
  } 
 
 
   public  const Int32 ULW_COLORKEY =  0x00000001 ; 
   public  const Int32 ULW_ALPHA =  0x00000002 ; 
   public  const Int32 ULW_OPAQUE =  0x00000004 ; 
 
   public  const  byte AC_SRC_OVER =  0x00 ; 
   public  const  byte AC_SRC_ALPHA =  0x01 ; 
 
 
  [DllImport( " user32.dll " , ExactSpelling =  true , SetLastError =  true )] 
   public  static  extern Bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref Point pptDst, ref Size psize, IntPtr hdcSrc, ref Point pprSrc, Int32 crKey, ref BLENDFUNCTION pblend, Int32 dwFlags); 
 
  [DllImport( " user32.dll " , ExactSpelling =  true , SetLastError =  true )] 
   public  static  extern IntPtr GetDC(IntPtr hWnd); 
 
  [DllImport( " user32.dll " , ExactSpelling =  true )] 
   public  static  extern  int ReleaseDC(IntPtr hWnd, IntPtr hDC); 
 
  [DllImport( " gdi32.dll " , ExactSpelling =  true , SetLastError =  true )] 
   public  static  extern IntPtr CreateCompatibleDC(IntPtr hDC); 
 
  [DllImport( " gdi32.dll " , ExactSpelling =  true , SetLastError =  true )] 
   public  static  extern Bool DeleteDC(IntPtr hdc); 
 
  [DllImport( " gdi32.dll " , ExactSpelling =  true )] 
   public  static  extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject); 
 
  [DllImport( " gdi32.dll " , ExactSpelling =  true , SetLastError =  true )] 
   public  static  extern Bool DeleteObject(IntPtr hObject); 
 
  [DllImport( " user32.dll " , EntryPoint =  " SendMessage " )] 
   public  static  extern  int SendMessage( int hWnd, int wMsg, int wParam, int lParam); 
  [DllImport( " user32.dll " , EntryPoint =  " ReleaseCapture " )] 
 
   public  static  extern  int ReleaseCapture(); 
   public  const  int WM_SysCommand =  0x0112 ; 
   public  const  int SC_MOVE =  0xF012 ; 
 
   public  const  int SC_MAXIMIZE =  61488 ; 
   public  const  int SC_MINIMIZE =  61472 ; 
}