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

Problem/Question/Abstract:

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

Answer:

{ ... }
const
  WS_EX_LAYERED = $80000;
  LWA_COLORKEY = 1;
  LWA_ALPHA = 2;

type
  TSetLayeredWindowAttributes = function(
    hwnd: HWND; {handle to the layered window}
    crKey: TColor; {specifies the color key}
    bAlpha: byte; {value for the blend function}
    dwFlags: DWORD {action}
    ): BOOL; stdcall;

procedure TfBaseSplash.FormCreate(Sender: TObject);
var
  Info: TOSVersionInfo;
  F: TSetLayeredWindowAttributes;
begin
  inherited;
  Info.dwOSVersionInfoSize := SizeOf(Info);
  GetVersionEx(Info);
  if (Info.dwPlatformId = VER_PLATFORM_WIN32_NT) and (Info.dwMajorVersion >= 5) then
  begin
    F := GetProcAddress(GetModulehandle(user32), 'SetLayeredWindowAttributes');
    if Assigned(F) then
    begin
      SetWindowLong(Handle, GWL_EXSTYLE, GetWindowLong(Handle, GWL_EXSTYLE)
        or WS_EX_LAYERED);
      F(Handle, 0, Round(255 * 80 / 100), LWA_ALPHA);
    end;
  end;
end;