procedure TForm1.ShowSystemMenu(const LPt: TPoint);
var
  LMenu: HMENU;
  LFlags: Cardinal;
  LCommand: LongWord;
begin
  LMenu := GetSystemMenu(FParentForm.Handle, False);
  LFlags := TPM_RETURNCMD or GetSystemMetrics(SM_MENUDROPALIGNMENT);
  LCommand := LongWord(TrackPopupMenu(LMenu, LFlags, LPt.X, LPt.Y, 0, FParentForm.Handle, nil));
  PostMessage(FParentForm.Handle, WM_SYSCOMMAND, LCommand, 0);
end;