title: Scaling a QPolygon or QPolygonF
body: <p>I need to scale a polygon.</p>
  
  <p>write the following</p>
  
  <p>Qt Code:</p>
  
  <pre><code>QPolygonF qpf=QPolygonF(QPolygon(4,points));
  QTransform trans;
  trans=trans.scale(1.5,1.5);
  QPolygonF qpf2=trans.map(qpf);
  path.addPolygon(qpf2);
  </code></pre>
  
  <p>for the points:</p>
  
  <p>Qt Code:</p>
  
  <pre><code>  static const int points[8] = {
      10, 80,
      20, 10,
      80, 30,
      90, 70
      };
  </code></pre>
  
  <p>it generates
  ---15,120--
  ---30,15--
  ---120,45--
  ---135,105--</p>
  
  <p>thus it moves slightly too.</p>
  
  <p>is there a way to scale from center? 
  for example origin of the shape should be the same point after scaling.
  is there a built in way or must i calculate all the points again to scale?
  thanks</p>