Qt Graphics，向前或向后移动对象

Question

I have two object: CQWater and CQTank. My CQTank will disappear if he has the same position. What should I do to move a tank forward.

CQWater::CQWater( QGraphicsScene *scena )
{
    // drew the rect
       setPixmap(QPixmap(":/new/prefix1/images/woda.png"));
       setTransformOriginPoint(50,50);
       setRotation(180);

 woda = new CWater();
 setPos(woda->x, woda->y);
 scena->addItem(this);

}

TANK:

CQTank::CQTank( QGraphicsScene *scena )
{
     czolg = new CTank();
     setPos(czolg->x, czolg->y);
     scena->addItem(this);
}


QRectF CQTank::boundingRect() const
{
    qreal adjust = 0.5;
    return QRectF(-18 - adjust, -22 - adjust,
                  36 + adjust, 60 + adjust);
}


QPainterPath CQTank::shape() const
{
   QPainterPath path;
   path.addRect(-10, -20, 20, 40);
   return path;
}


void CQTank::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    painter->setBrush(Qt::yellow);
    painter->drawEllipse(-10, -10, 20, 20);
}

I don't know how move an object forward or backward.

Answer 1

You have to use the Z-value property, as the docs say:

void QGraphicsItem::setZValue(qreal z)

Sets the Z-value of the item to z. The Z value decides the stacking order of sibling (neighboring) items. A sibling item of high Z value will always be drawn on top of another sibling item with a lower Z value.

If you restore the Z value, the item's insertion order will decide its stacking order.

The Z-value does not affect the item's size in any way.

The default Z-value is 0.

The larger it is with respect to another one, it will be shown above, otherwise it will be below.