Getting image from FBO

#include <QtCore>
#include <QtGui>
#include <QtWidgets>
 
QImage createImageWithFBO()
{
    QSurfaceFormat format;
    format.setMajorVersion(3);
    format.setMinorVersion(3);
 
    QWindow window;
    window.setSurfaceType(QWindow::OpenGLSurface);
    window.setFormat(format);
    window.create();
 
    QOpenGLContext context;
    context.setFormat(format);
    if (!context.create())
        qFatal("Cannot create the requested OpenGL context!");
    context.makeCurrent(&window);
 
    const QRect drawRect(0, 0, 400, 400);
    const QSize drawRectSize = drawRect.size();
 
    QOpenGLFramebufferObjectFormat fboFormat;
    fboFormat.setSamples(16);
    fboFormat.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
 
    QOpenGLFramebufferObject fbo(drawRectSize, fboFormat);
    fbo.bind();
 
    QOpenGLPaintDevice device(drawRectSize);
    QPainter painter;
    painter.begin(&device);
    painter.setRenderHints(QPainter::Antialiasing | QPainter::HighQualityAntialiasing);
 
    painter.fillRect(drawRect, Qt::blue);
 
    painter.drawTiledPixmap(drawRect, QPixmap(":/qt-project.org/qmessagebox/images/qtlogo-64.png"));
 
    painter.setPen(QPen(Qt::green, 5));
    painter.setBrush(Qt::red);
    painter.drawEllipse(0, 100, 400, 200);
    painter.drawEllipse(100, 0, 200, 400);
 
    painter.setPen(QPen(Qt::white, 0));
    QFont font;
    font.setPointSize(24);
    painter.setFont(font);
    painter.drawText(drawRect, "Hello FBO", QTextOption(Qt::AlignCenter));
 
    painter.end();
 
    fbo.release();
    return fbo.toImage();
}
 
int main(int argc, char **argv)
{
    QApplication app(argc, argv);
 
    QImage targetImage = createImageWithFBO();
 
    QLabel label;
    label.setPixmap(QPixmap::fromImage(targetImage));
    label.show();
    return app.exec();
}