var 
  DC: hdc; 
  Pen: HPen; 
  penwidth: integer; 
 
procedure TForm1.FormCreate(Sender: TObject); 
begin 
  penwidth := 5; 
  DC := GetDc(Richedit1.Handle); 
  Pen := CreatePen(PS_Solid, penwidth, RGB(255, 0, 0)); 
  SelectObject(DC, Pen); 
end; 
 
procedure TForm1.FormDestroy(Sender: TObject); 
begin 
  DeleteObject(Pen); 
  DeleteDC(DC); 
end; 
 
procedure TForm1.Button1Click(Sender: TObject); 
begin 
  MoveToEx(Dc, 10, 10, nil); 
  LineTo(Dc, Richedit1.clientwidth - 10, 10); 
  LineTo(Dc, Richedit1.clientwidth - 10, Richedit1.clientheight - 10); 
  LineTo(Dc, 10, Richedit1.clientheight - 10); 
  LineTo(Dc, 10, 10 - ord(not odd(penwidth))); 
end;