Tetszőleges Form átkapcsolása teljes képernyősre és vissza

procedure TFullScreen.SetFullScreen(const Value: boolean);
var
  f: TForm;
begin
  FFullScreen := Value;
  if Value<>FMode then begin
  FMode:=value;
  f:=Owner as TForm;
    if FMode then begin

      FOldWindowsLong:=GetWindowLong(f.Handle, GWL_STYLE);
      SetWindowLong(f.Handle, GWL_STYLE, GetWindowLong(f.Handle, GWL_STYLE) AND NOT WS_CAPTION);

      FOldHeight:=f.Height;
      FOldWidth:=f.Width;
      FOldLeft:=f.Left;
      FOldTop:=f.Top;

      FOldWindowsState:=f.WindowState;
      f.WindowState:=wsMaximized;
      f.ClientHeight:=Screen.Height;
      f.Clientwidth:=Screen.Width;
      f.Left:=0;
      f.Top:=0;
      f.Refresh;
    end else begin

      SetWindowLong(f.Handle, GWL_STYLE, FOldWindowsLong);
      f.height:=FOldHeight;
      f.width:=FOldWidth;
      f.Left:=FOldLeft;
      f.Top:=FOldTop;
      f.WindowState:=FOldWindowsState;
      f.Refresh;
    end;
  end;
end;