Qt reporting higher device pixel ratio with windows scaling and AA_EnableHighDpiScaling for a standard machine

[Chidambaram]

I am using a windows 10 machine. I am using Qt 5.12.11. This is the code I am using for a very simple app

int main(int argc, char *argv[])
{
    QApplication::setAttribute(Qt::AA_EnableHighDpiScaling, true);
    QApplication a(argc, argv);

    MainWindow w;
    w.show();
    return a.exec();
}

qreal MainWindow::detectDPR()
{
    QWidget* topWindow= this->window();
    float dpr;
    float dpi;
    float pdpi;
    topWindow->winId();
    if (topWindow->windowHandle()) {
        dpr = topWindow->windowHandle()->devicePixelRatio();
        dpi = (float)topWindow->windowHandle()->screen()->logicalDotsPerInch();
        pdpi = (float)topWindow->windowHandle()->screen()->physicalDotsPerInch();
    }

    qDebug() << dpi;
    qDebug() << dpr;
    qDebug() << pdpi;
}

These are the results I observe.

When the flag enable high dpi is set

• Scale 100%
  • DPI - 96
  • DPR - 1
  • PDPI - 96
• Scale 125%
  • DPI - 120
  • DPR - 1
  • PDPI - 96
• Scale 150%
  • DPI - 72
  • DPR - 2
  • PDPI - 48

When the flag is NOT set

• Scale 100%
  • DPI - 96
  • DPR - 1
  • PDPI - 96
• Scale 125%
  • DPI - 120
  • DPR - 1
  • PDPI - 96
• Scale 150%
  • DPI - 144
  • DPR - 1
  • PDPI - 96

I am running this program on a standard display where physical dpi is 96. It is interesting that, just because the scale is 150%, Qt is bumping the DPR to 2 where my actual machine is a standard machine and NOT a high DPI machine. In such cases, our UI widgets are getting messed up.

My questions

• Shouldn't DPR be related to physical DPI?
• Why is the physical DPI being reduced by a factor of DPR?

Thanks
Chid