I have a problem placing images on QGraphicsScene

franco.amato

I have a set of QImage objects (which are cuts from a larger image) and after some processing I have to place them on a QGraphicsScene at specific positions. No matter what position I specify, the image is always placed in the center.

This is the code I use to display every item (QImage)

void ImageViewer::displayImage(const QImage &image, const QPointF &position, qreal rotationAngle, qreal scaleFactor)
{
    QPixmap pixmap = QPixmap::fromImage(std::move(image));
    QPainter painter(&pixmap);
    QPen pen(Qt::blue, 1);
    painter.setPen(pen);
    painter.drawRect(pixmap.rect().adjusted(0, 0, -2, -2)); // the border

    QGraphicsPixmapItem *item = new QGraphicsPixmapItem(pixmap);
    // Adjust the position to account for the size of the cropped image
    QPointF adjustedPosition = position - QPointF(pixmap.width() / 2.0, pixmap.height() / 2.0);

    item->setPos(adjustedPosition); // <- not working
    item->setRotation(rotationAngle);
    item->setScale(scaleFactor);
    addItem(item);
}

Any idea on what I did wrong?

Pl45m4

@franco-amato said in I have a problem placing images on QGraphicsScene:

item->setPos(adjustedPosition); // <- not working

It is probably working, but you just don't see it.
AFAIK by default, the scene is centering around its first item.
The more items you add the more the scene will expand, but your view is focused on that first item, at whatever position it might be.

One solution (there might be other ways) is setting a fixed sceneRect like this:

QGraphicsView *view;
// either set view size or a size of your choice.
imageViewer->setSceneRect ( 0, 0, view->width(), view->height() );

franco.amato

Not working :( the item is still placed in the center

Pl45m4

@franco-amato said in I have a problem placing images on QGraphicsScene:

Not working :( the item is still placed in the center

Print the coordinates where you actually set your items to the scene.
What is postion and adjustedPosition ?

franco.amato

Coordinates are 10, 10

JonB

@franco-amato
I am a little lost. (10, 10) is as near to (0, 0) as damn-it, so wouldn't you expect it to be placed in the center?

franco.amato

I am also lost, I though the (0, 0) coordinates are placed at the top-left corner

Pl45m4

@franco-amato said in I have a problem placing images on QGraphicsScene:

I am also lost, I though the (0, 0) coordinates are placed at the top-left corner

The QGraphicsView yes, since it's a QWidget (all QWidgets have a top-left originated coodinate system).
However QGraphicsItems have their origin ( 0 / 0 ) at their center point.
So it could be possible that you set the scene position but expect a view port position.