#include <QApplication>
#include <QScreen>
#include <QTimer>
#include <QWidget>
#include <iostream>

int main(int argc, char **argv) {
    QApplication a(argc, argv);
    QWidget w; w.resize(640, 480); w.show();
    QTimer::singleShot(1000, [&] () {
        for( int i = 0; i < qApp->screens().size(); i++ ) {
           std::cout << "Screen factor: " << qApp->screens().at( i )->devicePixelRatio() << std::endl;
        }
        a.quit();
    });
    return a.exec();
}