Designing node editor widgets

overdrivr

Hi all,

I'm trying to code what I call a node editor with Qt (look blender node editor to get an idea). I've looked the example (draggable icons), and I've got some questions.

I'm wondering what is the "application/x-dnditemdata" format for the Mime-data. I looked in the doc, found nothing but I may have missed it.
What does QDragEnterEvent::setDropAction(Qt::MoveAction) ?
In the implementation of dropEvent(QDropEvent *event) in the example, why do we need to make a copy of the draggable QLabel pixmap, move the copy and then show() it, instead of just moving the original QLabel ? That seems a bit wasting ressources.

@void NodesWidget::dropEvent(QDropEvent *event)
{
if (event->mimeData()->hasFormat("application/x-dnditemdata"))
{
QByteArray itemData = event->mimeData()->data("application/x-dnditemdata");
QDataStream dataStream(&itemData, QIODevice::ReadOnly);

    QPixmap pixmap;
    QPoint offset;
    dataStream >> pixmap >> offset;

    QLabel *newIcon = new QLabel(this);
    newIcon->setPixmap(pixmap);
    newIcon->move(event->pos() - offset);
    newIcon->show();
    newIcon->setAttribute(Qt::WA_DeleteOnClose);

    if (event->source() == this)
    {
        event->setDropAction(Qt::MoveAction);
        event->accept();
    }
    else
    {
        event->acceptProposedAction();
    }
}
else
{
    event->ignore();
}

}@

I don't want to display a greyish version of the original QLabel at the original position, how should I modify this code to remove that ? Some parts of this code is little bit obscure to me

@void NodesWidget::mousePressEvent(QMouseEvent *event)
{
//On recupere le widget concerné par l'event (qui est un enfant de la fenetre actuelle)
QLabel child = static_cast<QLabel>(childAt(event->pos()));
if (!child)
return;

//On copie son image
QPixmap pixmap = *child->pixmap();

//??
QByteArray itemData;
QDataStream dataStream(&itemData, QIODevice::WriteOnly);
dataStream << pixmap << QPoint(event->pos() - child->pos());

//??
QMimeData *mimeData = new QMimeData;
mimeData->setData("application/x-dnditemdata", itemData);

QDrag *drag = new QDrag(this);
drag->setMimeData(mimeData);
drag->setPixmap(pixmap);
drag->setHotSpot(event->pos() - child->pos());

QPixmap tempPixmap = pixmap;
QPainter painter;
painter.begin(&tempPixmap);
painter.fillRect(pixmap.rect(), QColor(127, 127, 127, 127));
painter.end();

child->setPixmap(tempPixmap);

if (drag->exec&#40;Qt::CopyAction | Qt::MoveAction, Qt::CopyAction&#41; == Qt::MoveAction&#41;
    child->close();
else
{
    child->show();
    child->setPixmap(pixmap);
}

}@

Thanks for any help !

overdrivr

Anyone ?

sadaszewski

It's not a reply to your questions but maybe you will find it useful : http://algoholic.eu/qnodeseditor-qt-nodesports-based-data-processing-flow-editor/