Re: [Development] How fast grab a QML item's content to image when it updates?

[Denis Shienkov]

12.12.2017 16:13, Denis Shienkov пишет:

Hi all...

Is it possible to grab a QQuickItem content (e.g. with all sub-items)
when an item changes?

E.g. with widgets I use the following code:

bool MyWidget::event(QEvent *event)
{
    if (event->type() == QEvent::UpdateRequest)
        myGrab();
    return QWidget::event(event);
}

void MyWidget::myGrab()
{
    ...
    QBackingStore *store = backingStore();
    Q_ASSERT(store);

    QPaintDevice *pdev = store->paintDevice();
    const auto image = dynamic_cast<QImage *>(pdev);
    ...
}

it is very fast (as I know)...

But with the QML I got a troubles: I can 'grab' the sourceItem, using

the FBO and private functions, but the fbo::toImage() is too slow (~24 msecs),

and I don't know how to intercept the signal when a watched item updates:

Grabber::Grabber(QQuickItem *parent)
    : QQuickItem(parent)
{
    setFlag(QQuickItem::ItemHasContents);
}

// Where sourceItem - is a watched item.
void Grabber::setSourceItem(QQuickItem *sourceItem)
{
    if (sourceItem == m_sourceItem)
        return;
    m_sourceItem = sourceItem;
    emit sourceItemChanged(m_sourceItem);
    update();
}

QSGNode *Grabber::updatePaintNode(QSGNode *oldNode,

                                  UpdatePaintNodeData *updatePaintNodeData)

{
    Q_UNUSED(updatePaintNodeData);

    if (!m_sourceItem)
        return oldNode;

    QSGRootNode root;
root.appendChildNode(QQuickItemPrivate::get(m_sourceItem)->itemNode());

    const QScopedPointer<QSGRenderer> renderer(
                QQuickItemPrivate::get(this)->
                sceneGraphRenderContext()->createRenderer());

    renderer->setRootNode(&root);

    const QSize size(m_sourceItem->width(), m_sourceItem->height());
    renderer->setDeviceRect(size);
    renderer->setViewportRect(size);
    renderer->setProjectionMatrixToRect(QRectF(QPointF(), size));
    renderer->setClearColor(Qt::transparent);

    QOpenGLFramebufferObject fbo(size);
    renderer->renderScene(BindableFbo(&fbo));
    fbo.release();

    QElapsedTimer et;
    et.start();
    const QImage image = fbo.toImage(); // TOO LONG ~24 msec!
    qDebug() << "Elapsed:" << et.elapsed();

    return oldNode;
}

_______________________________________________
Development mailing list
Development@qt-project.org
http://lists.qt-project.org/mailman/listinfo/development