Share the same QGraphicsEffect for many QGraphicsItems

Question

What I do:

I am creating a new QGraphicsEffect in the constructor of my View (QMainWindow):

QGraphicsBlurEffect *m_blurEffect = new QGraphicsBlurEffect(this);
QGraphicsScene *m_scene = new GameGraphicsScene();
QGraphicsView *m_graphicsView = new QGraphicsView();
m_graphicsView->setScene(m_scene);

Then I create several QGraphicsItems:

QGraphicsItem *item = new QGraphicsItem;
item->setGraphicsEffect(m_blurEffect); //<< This Line is where I need help
m_scene->addItem(item);

I want all these QGraphicsItems to share the same QGraphicsBlurEffect, so that I can easily toggle enabled/disabled by calling

m_blurEffect->setEnabled(false); //(true)

in the View (where they get the pointer to the effect from.

What it does:

It appears that only one of these items contains the pointer, after the creating-progress. I used qDebug to show me if the pointer to m_blurEffect is correct after a new QGraphicsItem is created

for(...)
{
   QGraphicsItem *item= new TileGraphicsItem();
   item->setGraphicsEffect(m_blurEffect);
   qDebug() << m_blurEffect << tileItem->graphicsEffect();
}

The output is correct, something like:

qDebug(): [...]

QGraphicsBlurEffect(0x139fe120) QGraphicsBlurEffect(0x139fe120)

[...]

For more checking I let qDebug tell me the reference to m_blurEffect again, when I'm hovering my mouse over the Items. The result shows, that all of them have empty pointers

qDebug() << graphicsEffect();

QObject(0x0)

except the last item that was created, it contains the right reference (QGraphicsBlurEffect(0x139ce140) in my case).

So what can I do?

I want to achieve, that they all share the correct reference to one QGraphicsEffect* object that I created before they existed.

If necessary I can give further detail.

Pavel Strakhov Pavel Strakhov · Accepted Answer · 2013-12-14T21:25:41

QGraphicsEffects cannot be shared between several graphics items. You need to create an object of graphics effect for each graphics item. See the documentation of QGraphicsItem::setGraphicsEffect:

If effect is the installed on a different item, setGraphicsEffect() will remove the effect from the item and install it on this item. QGraphicsItem takes ownership of effect.

Share the same QGraphicsEffect for many QGraphicsItems

What I do:

What it does:

So what can I do?

1 Answers