Как узнать количество видимых строчек в TMemo

function LinesVisible(Memo: TMemo): integer;
var
  OldFont : HFont;
  Hand : THandle;
  TM : TTextMetric;
  Rect : TRect;
  tempint : integer;
begin
  Hand := GetDC(Memo.Handle);
  try
    OldFont := SelectObject(Hand, Memo.Font.Handle);
    try
      GetTextMetrics(Hand, TM);
      Memo.Perform(EM_GETRECT, 0, longint(@Rect));
      tempint := (Rect.Bottom - Rect.Top) div
      (TM.tmHeight + TM.tmExternalLeading);
    finally
      SelectObject(Hand, OldFont);
    end;
  finally
    ReleaseDC(Memo.Handle, Hand);
  end;
  Result := tempint;
end;