Po = [1 2 2 1;1 1 2 2;1 1 1 1];
hold on;

%plot(Po(1,1), Po(2,1));
%plot(Po(1,2), Po(2,2));
%plot(Po(1,3), Po(2,3));
%plot(Po(1,4), Po(2,4));

line([Po(1,1), Po(2,1)],[Po(1,2), Po(2,2)]);
line([Po(1,2), Po(2,2)],[Po(1,3), Po(2,3)]);
line([Po(1,3), Po(2,3)],[Po(1,4), Po(2,4)]);
line([Po(1,4), Po(2,4)],[Po(1,1), Po(2,1)]);

Xcentro = (max(Po(1,:)) + min(Po(1,:)))/2;
Ycentro = (max(Po(2,:)) + min(Po(2,:)))/2;
ang = 5;
figure;
while (ang<5000)
  T1 = [1 0 -Xcentro;0 1 -Ycentro;0 0 1];
  T2 = [cos(ang) -sin(ang) 0;sin(ang) cos(ang) 0;0 0 1];
  T3 = [1 0 Xcentro;0 1 Ycentro;0 0 1];
  Pt = (T3 * T2 * T1) * Po;
  H(1) = line([Pt(1,1), Pt(2,1)],[Pt(1,2), Pt(2,2)]);
  H(2) = line([Pt(1,2), Pt(2,2)],[Pt(1,3), Pt(2,3)]);
  H(3) = line([Pt(1,3), Pt(2,3)],[Pt(1,4), Pt(2,4)]);
  H(4) = line([Pt(1,4), Pt(2,4)],[Pt(1,1), Pt(2,1)]);
  drawnow;
  pause(0.01);
  ang = ang + 5;
  delete(H(:));
endwhile

hold off;