message: Implement both pixel-based and angle-based scroll
  This method is recommended in Qt documentation.
diff: @@ -139,8 +139,18 @@ QUndoCommand* Navigator::mouseDoubleClickEvent(QMouseEvent* e)
  QUndoCommand* Navigator::wheelEvent(QWheelEvent* e)
  {
  /// @todo Use scale for orthographic projections
  - // Zoom
  - zoom(m_renderer->scene().center(), -e->angleDelta() * 0.125);
  + // Amount to zoom
  + float d = 0.0f;
  +
  + QPoint numPixels = e->pixelDelta();
  + QPoint numDegrees = e->angleDelta() * 0.125;
  +
  + if (!numPixels.isNull())
  + d = numPixels.y();
  + else if (!numDegrees.isNull())
  + d = numDegrees.y();
  +
  + zoom(m_renderer->scene().center(), -d);
  e->accept();
  emit updateRequested();
  