Render hidden widget to QPixmap

#include <QtGui>int main(int argc, char *argv[]){    QApplication app(argc, argv);    QWidget *window = new QWidget;    QVBoxLayout *layout = new QVBoxLayout(window);    for (int i = 0; i < 10; i++) {        layout->addWidget(new QPushButton(QString("button %1").arg(i)));    }    window->adjustSize();    QPixmap pixmap(window->size());    window->render(&pixmap);    pixmap.save("screenshot.png");    return 1;}