#include <QApplication>
#include <QGLWidget>
#include <QTimer>
#include <QDebug>
#include <QResizeEvent>

class MyGLWidget : public QGLWidget
{
    Q_OBJECT
public:
    MyGLWidget(QWidget *parent = 0) : QGLWidget(parent) {}
public slots:
    void resizeTheWidget()
    {
        qDebug("Before resizing");
        resize(300, 600);
        qDebug() << "Done the resize";
    }
protected:
    void resizeEvent(QResizeEvent *e)
    {
        qDebug() << "Resizing the glwidget" << e->size();
    }
};

#include "main.moc"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QWidget w;
    w.setFixedSize(300, 600);
    MyGLWidget *gl = new MyGLWidget(&w);
    gl->setGeometry(0, 0, 150, 300);
    QTimer::singleShot(1000, gl, SLOT(resizeTheWidget()));
    w.show();
    return a.exec();
}