[Qt-interest] update qgraphicsscene

[caius ligarius]

Thanks it works. I was trying to "setSceneRect" using QGraphicsVIew
dimension and not QImage.

Yes, you are right this was meant to be pseudo-code and I am acutally using
QGraphicsPixmapItem and not QGraphicsItem - apologies!

Do you know I can delete QGraphicsPixmap item in the destructor?

Thanks,
Caius

On Mon, May 24, 2010 at 12:58 PM, Murphy, Sean M. <sean.murphy at gd-ais.com>wrote:

> > I have the need to update a QGraphicsView widget with a new QImage
> everytime I call a certain function
> > ("populateScene"). Currently I create  a new QGraphicsScene instance
> everytime I call this function, is
> > there some better way to update the scene without creating a new instance
> of QGraphicsScene every time?
> > (I am assuming this would slow things down and also I will not be able to
> delete the QGraphicsScene
> > pointer at the end since this would clear the image from the viewport).
> My code below-
> >
> > void populateScene(QImage* image)
> > {
> >   QGraphicsScene* scene = new QGraphicsScene;
> >   QPixmap np = QPixmap::fromImage(*image);
> >
> >   qGraphicsItem->setPixmap(np);
> >   scene->addItem(qGraphicsItem);
> >
> >   qgraphicsView->setPixmap(np);
> >
> > }
>
> It looks like what you've got above is pseudo code since a few of your
> lines won't compile.  QGraphicsItem doesn't have setPixmap(), that's
> QGraphicsPixmapItem, and QGraphicsView also doesn't have a setPixmap()
> function.
>
> > qGraphicsItem: QGraphicsItem, initialized in the constructor
> > qgraphicsView: QGRaphicsView, initialized in constructor
>
> Anyways, what you want to do is move your scene initialization to the
> constructor, as well as your QGraphicsPixmapItem initialization.  From what
> you've told us, you'll only need one of each for the lifetime of the
> application.
>
> The just make populateScene be:
>
> void populateScene(QImage* image)
> {
>  qGraphicsPixmapItem->setPixmap(QPixmap::fromImage(*image));
>  scene->setSceneRect(0,0,image->width(), image->height());
> }
>
> You could add a qgraphicsView->centerOn(x,y) if you want to guarantee the
> new image is centered.
> Sean
>
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