pinvoke.net: Edit: user32.SetLayeredWindowAttributes

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Summary: The SetLayeredWindowAttributes API

!!!!C# Signature:
 [DllImport("user32.dll")]
 static extern bool SetLayeredWindowAttributes(IntPtr hwnd, uint crKey, byte bAlpha, uint dwFlags);
!!!!VB Signature:
 Public Declare Auto Function SetLayeredWindowAttributes Lib "User32.Dll" _
        (ByVal hWnd As IntPtr, ByVal crKey As Integer, ByVal Alpha As Byte, ByVal dwFlags As Integer) As Boolean
!!!!PB Signature:
 Function Long SetLayeredWindowAttributes(long hWnd, Long crKey , char /*Byte*/ bAlpha , Long dwFlags) &
 	Library "user32" alias for "SetLayeredWindowAttributes;Ansi" 
!!!!User-Defined Types:
None.

!!!!Notes:
This method may only be called on Windows 2000 and above.

!!!!Tips & Tricks:

!!!!Sample Code:
        public const int GWL_EXSTYLE = -20;
        public const int WS_EX_LAYERED = 0x80000;
        public const int LWA_ALPHA = 0x2;
        public const int LWA_COLORKEY = 0x1;

//set the window style to alpha appearance
        private void button4_Click(object sender, EventArgs e)
        {
            SetWindowLong(Handle, GWL_EXSTYLE, GetWindowLong(Handle, GWL_EXSTYLE) ^ WS_EX_LAYERED);
            SetLayeredWindowAttributes(Handle, 0, 128, LWA_ALPHA);
        }

!!!!Sample PB Code:
  // Tip submitted by Olivier Citeau (ociteau@yahoo.fr)
  // Combined it with the numeric module from Simon Harris (simon@addease.com.au)
  // As found on the PBDR.com website
  
  //Open event of your window
  Constant long LWA_COLORKEY = 1, LWA_ALPHA = 2
  Constant long GWL_EXSTYLE = - 20
  Constant long WS_EX_LAYERED = 524288 //2^19
  Long ll_Ret, ll_handle
  
  n_cst_numerical lnc_N
  
  // Set the window style to 'Layered'
  ll_handle = Handle (this)
  ll_Ret = GetWindowLong(ll_handle, GWL_EXSTYLE)
  
  //ll_Ret = ll_Ret Or WS_EX_LAYERED
  ll_Ret = lnc_N.of_bitwiseor( ll_Ret, WS_EX_LAYERED)
  
  SetWindowLong (ll_handle, GWL_EXSTYLE, ll_Ret)
  
  // Set the opacity of the layered window to 128
  SetLayeredWindowAttributes (ll_handle, 0, char(128),LWA_ALPHA)
  
  //Note that if you set opacity to 0, your window will be
  //invisible. With 255, it will be a "normal" window.

!!!!Alternative Managed API:
When setting Layered Window Attributes for window transparency, you can set the .Opacity property of your form instead.

Documentation: SetLayeredWindowAttributes@msdn on MSDN