Author: Tomas Rutkauskas 

How to use the alpha transparency features included in Windows 2000 and XP

Answer:

1   { ... }
2   const
3     WS_EX_LAYERED = $80000;
4     LWA_COLORKEY = 1;
5     LWA_ALPHA = 2;
6   
7   type
8     TSetLayeredWindowAttributes = function(
9       hwnd: HWND; {handle to the layered window}
10      crKey: TColor; {specifies the color key}
11      bAlpha: byte; {value for the blend function}
12      dwFlags: DWORD {action}
13      ): BOOL; stdcall;
14  
15  procedure TfBaseSplash.FormCreate(Sender: TObject);
16  var
17    Info: TOSVersionInfo;
18    F: TSetLayeredWindowAttributes;
19  begin
20    inherited;
21    Info.dwOSVersionInfoSize := SizeOf(Info);
22    GetVersionEx(Info);
23    if (Info.dwPlatformId = VER_PLATFORM_WIN32_NT) and (Info.dwMajorVersion >= 5) then
24    begin
25      F := GetProcAddress(GetModulehandle(user32), 'SetLayeredWindowAttributes');
26      if Assigned(F) then
27      begin
28        SetWindowLong(Handle, GWL_EXSTYLE, GetWindowLong(Handle, GWL_EXSTYLE)
29          or WS_EX_LAYERED);
30        F(Handle, 0, Round(255 * 80 / 100), LWA_ALPHA);
31      end;
32    end;
33  end;