message: Avoid using QWheelEvent::pixelDelta() on X11
  According to the Qt5 docs it's unreliable on this platform.
diff: #include <avogadro/rendering/glrenderer.h>
  #include <avogadro/rendering/scene.h>
  +#include <QtGui/QGuiApplication>
  #include <QtCore/QSettings>
  #include <QtGui/QKeyEvent>
  #include <QtGui/QMouseEvent>
  @@ -167,10 +168,11 @@ QUndoCommand* Navigator::wheelEvent(QWheelEvent* e)
  QPoint numPixels = e->pixelDelta();
  QPoint numDegrees = e->angleDelta() * 0.125;
  - if (!numPixels.isNull())
  - d = numPixels.y();
  + // see https://doc.qt.io/qt-5/qwheelevent.html#pixelDelta
  + if (!numPixels.isNull() && QGuiApplication::platformName().toStdString().compare("xcb"))
  + d = numPixels.y(); // use pixelDelta() when available, except on X11
  else if (!numDegrees.isNull())
  - d = numDegrees.y();
  + d = numDegrees.y(); // fall back to angleDelta()
  zoom(m_renderer->camera().focus(), m_zoomDirection * d);
  