QMainWindow take high quality screenshot with transparency

MainWindow.cpp

// SPDX-License-Identifier: CC0-1.0
// Creative Commons Zero v1.0 Universal License: https://creativecommons.org/publicdomain/zero/1.0/deed

void MainWindow::takeScreenshot()
{
    assert(isVisible() || !"call show() before taking screenshot");
    
    QPixmap pixmap(size() * devicePixelRatioF());
    pixmap.setDevicePixelRatio(devicePixelRatioF());

    pixmap.fill(Qt::transparent);
    render(&pixmap);
    pixmap.save("screenshot.png");
}