title: what is the qtransform in QGraphicsScene::itemAt()
body: <p>I create a custom <code>QGraphicsItem</code>. And overwrite the <code>boundingRect()</code> and <code>paint()</code>.</p>
  
  <pre><code>QRectF myTile::boundingRect() const
  {
    return QRectF(xPos*10, yPos*10, 10, 10);
  }
  
  void myTile::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
  {
    QRectF rec = boundingRect();
    int gvi = value * 255;
    QColor gv(gvi, gvi, gvi, 255);
    QBrush brush(gv);
    painter-&gt;fillRect(rec, brush);
    painter-&gt;drawRect(rec);
  }
  </code></pre>
  
  <p>Then I use <code>addItem()</code> to add a item to a scene. Now I want to get it from the scene by its position. I find the <code>itemAt</code> function. But the problem is I don't know what is the <code>const QTransform</code> &amp; <code>deviceTransform</code>. What should I use for the <code>QTransform</code>?. </p>
  
  <p>Because I didn't implement any transform in the <code>QGraphicsItem</code>. This confuses me. </p>