auto scene = new QGraphicsScene;
auto graphicsView = new QGraphicsView { scene };
setCentralWidget(graphicsView);

auto sky = scene->addPixmap(QStringLiteral(":/icons/sky.png"));
std::array<QGraphicsItem *, 6> items = {
   scene->addPixmap(QStringLiteral(":/icons/clouds_1.png")),
   scene->addPixmap(QStringLiteral(":/icons/clouds_2.png")),
   scene->addPixmap(QStringLiteral(":/icons/clouds_3.png")),
   scene->addPixmap(QStringLiteral(":/icons/rocks_1.png")),
   scene->addPixmap(QStringLiteral(":/icons/clouds_4.png")),
   scene->addPixmap(QStringLiteral(":/icons/rocks_2.png"))
};
scene->setSceneRect(sky->boundingRect());
graphicsView->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
graphicsView->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
setFixedSize(sky->boundingRect().size().toSize());

connect(&_timer, &QTimer::timeout, this, [items, sky](){
   for (int i = 0; i < 6; ++i)
      items[i]->setX(items[i]->x() > -sky->boundingRect().width() ? items[i]->x()-(i+1):0);
});
_timer.start(1000 / 33);