setRect vs boundingRect

[zgulser]

Hi,

I got confused with the boundingRect. Since setRect sets the coodinate system of the corresponding item, what is boundingRect used for. I mean only setRect seems enough. What is the difference?

Regards

[jpn]

But setRect() is not part of any QGraphicsItem but just QGraphicsRectItem (and QGraphicsEllipseItem) where it makes perfect sense.

[zgulser]

Hi again,

Yeah I mean QGraphicsRectItem or QGraphicsEllipseItem in which setRect method exists. But if we once make item.setRect(...), don't we already have a bounding rect?

Regards

[jpn]

Yeah I mean QGraphicsRectItem or QGraphicsEllipseItem in which setRect method exists. But if we once make item.setRect(...), don't we already have a bounding rect?

What do you mean? QGraphicsRectItem uses that rect (adjusted with pen width) as bounding rect. But other items in general don't have any setRect() method. The bounding rect is used by the graphics scene.

[zgulser]

More clearly;

For example, QGraphicsEllipseItem.setRect() = QGraphicsEllipseItem.boundingRect() ?

Regards

[wysota]

Looking at the source code is a good way to answer your question (although J-P has already answered it a couple of times):

QRectF QGraphicsRectItem::boundingRect() const
{
    Q_D(const QGraphicsRectItem);
    if (d->boundingRect.isNull()) {
        qreal halfpw = pen().widthF() / 2;
        d->boundingRect = d->rect;
        if (halfpw > 0.0)
            d->boundingRect.adjust(-halfpw, -halfpw, halfpw, halfpw);
    }
    return d->boundingRect;
}

QRectF QGraphicsRectItem::boundingRect() const
{
    Q_D(const QGraphicsRectItem);
    if (d->boundingRect.isNull()) {
        qreal halfpw = pen().widthF() / 2;
        d->boundingRect = d->rect;
        if (halfpw > 0.0)
            d->boundingRect.adjust(-halfpw, -halfpw, halfpw, halfpw);
    }
    return d->boundingRect;
}

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Especially take a look at line #6.

d->rect is set by QGraphicsRectItem::setRect().