QGraphicsItem flickering

[michalk]

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:

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();
}

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();
}

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

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);

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);

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I make position updates in advance method.

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;
 
}

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;

}

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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.

[wysota]

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

[michalk]

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

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;
}

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;
}

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[wysota]

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

[michalk]

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.