title: Scale x-axis of QChartView using mouse wheel
body: <p>In my application I use <code>QChart</code> to show line graph. Unfortunately Qt Charts doesn't support such basic functions as zooming using mouse wheel and scrolling by mouse. Yes, there is RubberBand functionality but that still doesn't support scrolling etc end that isn't so intuitive to users. Also I need to scale only x-axis, some kind of <code>setRubberBand(QChartView::HorizontalRubberBand)</code> but using mouse wheel.
  So far, after diving into <code>QChartView</code> I've use the following workaround:</p>
  
  <pre><code>class ChartView : public QChartView {
  protected:
      void wheelEvent(QWheelEvent *event) Q_DECL_OVERRIDE
      {
          QRectF rect = chart()-&gt;plotArea();            
          if(event-&gt;angleDelta().y() &gt; 0)
          {
              rect.setX(rect.x() + rect.width() / 4);
              rect.setWidth(rect.width() / 2);                                   
          }
          else
          {
              qreal adjustment = rect.width() / 2;
              rect.adjust(-adjustment, 0, adjustment, 0);                    
          }            
          chart()-&gt;zoomIn(rect);
          event-&gt;accept();            
          QChartView::wheelEvent(event);
      }
  }
  </code></pre>
  
  <p>That works but zooming in and then zooming out doesn't lead to the same result. There is a small deviation. After debuging I've found that <code>chart()-&gt;plotArea()</code> always returns the same rect, so this workaround was useless. </p>
  
  <p>It there some way to get rect of a visible area only?
  Or may be someone could point me to the right solution how to do zooming/scrolling by mouse for QChartView?</p>