Question

I was looking a proper way to implment a “ScaleAnimation”. My purpose is to animate a QImage:

    timeline = new QTimeLine(time);
    timeline->setFrameRange(0, 100);
    animation = new QGraphicsItemAnimation;

    QRectF rect = item->boundingRect();
    int h = rect.bottom() - rect.top();
    int w = rect.right() - rect.left();


    animation->setItem(item);
    animation->setTimeLine(timeline);


    for (int i = 0; i < 100; i++) {
            int x = w + (int)((float)w*(float)(i/100.0));
            qreal xx = (qreal)(x)/(qreal)w;
            int y = (h) + (int)((float)h*(float)(i/100.0));
            qreal yy = (qreal)(y)/(qreal)h;          
            animation->setScaleAt(i/100, xx, yy);
    }

it seems to work but the origin of the animation seems to be (0, 0). Is there any way to apply the animation in (w/2, h/2)? Is there a better and more efficent (or correct) way to rewrite the animation? I am quit newbee in the Qt world.

thank you for your patience.

Answer 1

If you’re using a QGraphicsPixmapItem, simply set its offset to the midpoint, and move it by the same amount to counter the effects of setting the offset.

const QSizeF size = item->boundingRect().size()*0.5;
item->setOffset(size.width(), size.height());
item->moveBy(size.width(), size.height());