#include <QApplication>
#include <QQuickView>
#include <QQuickItem>
#include <QWidget>

template <typename T>
void updateMask(T* window)
{
    int arrowHeight = 12;
    int arrowWidth = 12;
    int hw = window->width() / 2;

    QPolygon polygon;
    polygon << QPoint(0, arrowHeight) << QPoint(0, window->height())
            << QPoint(window->width(), window->height()) << QPoint(window->width(), arrowHeight)
            << QPoint(hw+arrowWidth, arrowHeight)
            << QPoint(hw, 0)
            << QPoint(hw-arrowWidth, arrowHeight);

    QRegion region(polygon);

    window->setMask(region);
}

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QQuickView window;
    window.setTitle("qquickview");
    window.resize(800, 600);
    window.show();
    updateMask(&window);

    QWidget w;
    w.setWindowTitle("mask widget");
    w.resize(800, 600);
    w.show();
    updateMask(&w);

    return app.exec();
}