QGraphicsItem flickering

I have following problem:
I have a BallItem class derived from QGraphicsItem.
When I update position of my BallItem, Ballitem is flickering and sometimes in the screen (QGraphicsView) there are some remains left.

I attach source code of overrode methods:

Code:

---

BallItem::BallItem(qreal aPosX, qreal aPosY, qreal aRadius,QGraphicsItem *aParent) :
    QGraphicsItem(aParent),
    iVx(0),iVy(0),iRadius(aRadius)
{
    setPos(aPosX,aPosY);
}
 
 
QRectF BallItem::boundingRect() const
{
    qreal adjust = 0.5;
    QRectF rectf = QRectF(-iRadius-adjust,-iRadius-adjust,iRadius*2 + adjust
			  ,iRadius*2 + adjust);
    return rectf;
}
 
 
void BallItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
		     QWidget *widget)
{
    painter->save();
 
    painter->setBrush(Qt::red);
    painter->drawEllipse(QPointF(0,0),iRadius,iRadius);
 
    painter->restore();
}

---

Here I initialise QGraphicsView(iGameView) and QGraphicsScene(iGameScene)

Code:

---

iGameView->setRenderHint(QPainter::Antialiasing);
iGameView->setCacheMode(QGraphicsView::CacheBackground);
iGameView->setViewportUpdateMode(QGraphicsView::BoundingRectViewportUpdate);
iGameView->setBackgroundBrush(Qt::green);
iGameView->setAttribute(Qt::WA_LockPortraitOrientation, true);
 
iGameScene->setItemIndexMethod(QGraphicsScene::NoIndex);
 
iGameView->setScene(iGameScene);

---

I make position updates in advance method.

Code:

---

void BallItem::advance(int phase)
{
    if (!phase)
	return;
 
    bool flipX = false;
    bool flipY = false;
 
    qreal newX = x();
    qreal newY = y();
 
    if (newX + iRadius + iVx > scene()->width())
    {
	newX = scene()->width() - iRadius;
	flipX = true;
    }
    else if (newX - iRadius +iVx < 0)
    {
	newX = iRadius;
	flipX = true;
    }
    else
	newX+=iVx;
 
    if (newY + iRadius + iVy > scene()->height())
    {
	newY = scene()->height() - iRadius;
	flipY = true;
    }
    else if (newY - iRadius + iVy < 0)
    {
	newY = iRadius;
	flipY = true;
    }
    else
	newY+=iVy;
 
    setPos(newX,newY);
 
    if (flipX)
	iVx = -iVx;
 
    if (flipY)
	iVy = -iVy;
 
}

---

I am sorry for attaching so much source code but I know that there are some issues about mapping from item coordinate system to scene coordinate system and maybe I do something wrong in presented source code. Something what will be caught by more experienced eye.

You are drawing outside your boundingRect(). Calling setPos() in the item constructor doesn't make much sense either.

Do you mean adding adjust*2 when I specify rectf width and height?

Code:

---

QRectF BallItem::boundingRect() const
{
qreal adjust = 0.5;
QRectF rectf = QRectF(-iRadius-adjust, -iRadius-adjust, iRadius*2 + adjust*2
     , iRadius*2  + adjust*2);
 
return rectf;
}

---

Simplify the code (QRectF has a bunch of nice methods). And what's the purpose of calling setPos() in the constructor?

I am going to rewrite it so it will look better.

If it comes to constructor, hmm well it is a remaining from my try-outs, setPos() is going to be removed. Now I know it is not the best way to do so, but when I started with QGraphics... stuff I didn't know that.