performance issue(QGV + QPixmap::grabWidget)

[momesana]

Thanks for the reply wysota. According to your suggestions, I have changed the function createItems in the following way:

for (int i=0; i<tabWidget->count(); i++) {
    foreach(QGraphicsItem *item, items) {
        delete(item);
    }
    invalidate(sceneRect());
    items.clear();
 
    int batchSz = 4;
    for (int i=0; i<tabWidget->count(); i++) {
        QWidget *w = tabWidget->widget(i);
        QPixmap pm = QPixmap::grabWidget(w);
        pm = pm.scaled(300,200, Qt::IgnoreAspectRatio);
        ThumbnailItem * item = new ThumbnailItem(pm, i); // TODO Take size from config
        items << item;
        connect(item, SIGNAL(tabSelected(int)), tabWidget, SLOT(onTabSelected(int)));
        connect(item, SIGNAL(tabSelected(int)), this, SIGNAL(toggleThumbnailMode()));
        if (items.count() % batchSz == 0) {
            foreach(QGraphicsItem *i, items.mid(items.count()-4))
                addItem(i);
            QCoreApplication::processEvents();
        }
    }
    foreach(QGraphicsItem *i, items.mid(items.count() - items.count()%batchSz))
        addItem(i);
}

for (int i=0; i<tabWidget->count(); i++) {
    foreach(QGraphicsItem *item, items) {
        delete(item);
    }
    invalidate(sceneRect());
    items.clear();
    
    int batchSz = 4;
    for (int i=0; i<tabWidget->count(); i++) {
        QWidget *w = tabWidget->widget(i);
        QPixmap pm = QPixmap::grabWidget(w);
        pm = pm.scaled(300,200, Qt::IgnoreAspectRatio);
        ThumbnailItem * item = new ThumbnailItem(pm, i); // TODO Take size from config
        items << item;
        connect(item, SIGNAL(tabSelected(int)), tabWidget, SLOT(onTabSelected(int)));
        connect(item, SIGNAL(tabSelected(int)), this, SIGNAL(toggleThumbnailMode()));
        if (items.count() % batchSz == 0) {
            foreach(QGraphicsItem *i, items.mid(items.count()-4))
                addItem(i);
            QCoreApplication::processEvents();
        }
    }
    foreach(QGraphicsItem *i, items.mid(items.count() - items.count()%batchSz))
        addItem(i);
}

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Now the switch to thumbnail-mode is immediate which is a good thing. But, now the users see the items being created which is not optimal. Is it expensive to add some QGV Animation to hide this from the user? Maybe to display an opaque QGraphicsRectItem that covers the whole scene and then fading it out using QTimeLine in conjunction with QGraphicsItemAnimation?

Thanx