Не, решил так-то так (на Windows):
C++ (Qt)
#include <QApplication>
#include <QDesktopWidget>
#include <QQuickView>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQuickView view;
view.setSource(QUrl(QStringLiteral("qrc:/main.qml")));
view.showFullScreen();
const QDesktopWidget *desktop = QApplication::desktop();
if (desktop->isVirtualDesktop())
view.resize(desktop->width(), desktop->height());
return app.exec();
}