title: Custom QGraphicsView is painting on other widgets
body: <p>In Qt/c++, I have an overloaded/custom QGraphicsView class.
  In this classes' drawBackground event function (same issue happens with paintEvent), I am drawing some lines using the provided Qpainter:</p>
  
  <pre><code>void myGraphicsView::drawBackground(QPainter *painter, const QRectF &amp;rect)
  {
      QGraphicsView::drawBackground(painter, rect);
      QPen pen;    
      pen.setWidth(2);
      painter-&gt;setPen(pen);
  
      painter-&gt;drawLine(rect.x(),rect.y(),rect.x()+rect.width(),rect.y()+rect.height());
  }
  </code></pre>
  
  <p>Initialization of the GraphicsView custom class:</p>
  
  <pre><code>myGraphicsView::myGraphicsView(GLWidget *myOpenGLWindow,QWidget * parent) : QGraphicsView(parent)
  {
      setDragMode(QGraphicsView::ScrollHandDrag);
      myScene=new actionEditorButtons(this);
      myScene-&gt;setMainView(this);
      setScene(myScene);
      setStyleSheet("background: transparent");
      setAlignment(Qt::AlignBottom);
  }
  </code></pre>
  
  <p>Initialization of the custom QGraphicsScene, with a button that gets "corrupted" with the line drawn in the custom graphicsview:</p>
  
  <pre><code>actionEditorButtons::actionEditorButtons(BrainClass *theBrain,int receivedActionNb,QObject *parent) : QGraphicsScene(parent)
  {
      beginButton = new QPushButton();
      beginButton-&gt;setIcon(QIcon(":/icons/actionBegin.png"));
      beginButton-&gt;setIconSize(QSize(40,40));
      beginButton-&gt;setFixedSize(QSize(40,40));
      beginButton-&gt;setStyleSheet("border: none");
      beginProxy=addWidget(beginButton);
      beginProxy-&gt;setPos(0,80);
      connect(beginButton, SIGNAL (released()),this, SLOT (handleBeginButton()));
  }
  </code></pre>
  
  <p>My issue is that this line is not only drawn on this custom QGraphicsView, but it is drawn too on all widgets added this scene. How can I only draw in the main graphicsView and not in the added widgets ?</p>