void FaceColors::on_boxSelection_clicked()
{
    Gui::View3DInventor* view = qobject_cast<Gui::View3DInventor*>(Gui::getMainWindow()->activeWindow());
    if (view) {
        Gui::View3DInventorViewer* viewer = view->getViewer();
        if (!viewer->isSelecting()) {
            viewer->startSelection(Gui::View3DInventorViewer::Rubberband);
            viewer->addEventCallback(SoMouseButtonEvent::getClassTypeId(), Private::selectionCallback, this);
            // avoid that the selection node handles the event otherwise the callback function won't be
            // called immediately
            SoNode* root = viewer->getSceneGraph();
            static_cast<Gui::SoFCUnifiedSelection*>(root)->selectionRole.setValue(false);
            d->view = viewer;
        }
    }
}