title: QRect on a QGraphicsScene
body: <p>This seems trivial, but I didn't found a solution. All I want to do is to set up a coordinate system a QGraphicsScene [-10, -10] to [10, 10] (f.e. with setSceneRect(-10, -10, 20, 20)) and to plot a QRect within the scene, using the coordinate system of the scene.</p>
  
  <pre><code>scene = new QGraphicsScene(-10.0, -10.0, 20.0, 20.0, ui-&gt;graphicsView);
  // scene is already a QGraphicsScene pointer defined in the .h
  ui-&gt;graphicsView-&gt;setScene(scene);
  scene-&gt;addRect(-8, -8, 4, 4);
  </code></pre>
  
  <p>What I am expecting in the example is a rectangle bounding at the left-bottom border. I also tried mapToScene() and fitInView(), but that also didn't brought me the expected result.</p>
  
  <p>Thanks for helping.</p>