[TRUCO DELPHI] Hacer un Formulario transparente.

procedure TForm1.FormCreate(Sender: TObject);
var
  FullRgn, ClientRgn, ButtonRgn: THandle;
  Margin, X, Y: Integer;
begin
  Margin := (Width - ClientWidth) div 2;
  FullRgn := CreateRectRgn(0, 0, Width, Height);
  X := Margin;
  Y := Height - ClientHeight - Margin;
  ClientRgn := CreateRectRgn
    (X, Y, X + ClientWidth, Y + ClientHeight);
  CombineRgn(FullRgn, FullRgn, ClientRgn, RGN_DIFF);
  X := X + Button1.Left;
  Y := Y + Button1.Top;
  ButtonRgn := CreateRectRgn
    (X, Y, X + Button1.Width, Y + Button1.Height);
  CombineRgn(FullRgn, FullRgn, ButtonRgn, RGN_OR);
  SetWindowRgn(Handle, FullRgn, True);
end;