How can I detect collision among QPixmaps and QGraphicsItems objects

DSlim

I pass the pmap to the MainTarget class by pointer, which was previously by reference. There isn't a specific line that the compiler is showing. It crashes on execution. I replaced main_targets[index] with targetItems since that should hold the QGraphicsPixmapItem items.

@void Dialog::setPixmaps()
{
//Targets are delivered every 1sec
Five_timer->start(1000);

QList<QGraphicsPixmapItem*> targetItems;
foreach(QPixmap pix, main_targets) {
QGraphicsPixmapItem* p_item = new QGraphicsPixmapItem(pix);
targetItems.append(p_item);
}

int StartY = 0;

//Random starting Y point between -140 and -389
StartY = (qrand() % (-400 + 150) -140);

index = (qrand() % 9);
{
    if(index % 2 == 0)
    {
        //When even is selected start at far right
        pmap = new MainTargets(targetItems[index], 0);
        pmap->setPos(345,StartY);
    }

    else
    {
        //When odd is selected start at far left
        pmap = new MainTargets(targetItems[index], 1);
        pmap->setPos(-325,StartY);

    }
}

scene->addItem(pmap);

}@

andreyc

Does it always crash on the same place?
Try to step through the function using a debugger.

What is the type of main_targets in line #9?

DSlim

QList<QPixmap> main_targets is the type.

Seems to fail at the QList::operator[].

That is why I think the main_target array seems to be the issue.

andreyc

How do you fill main_target?

DSlim

Guess that is where the problem is I thought the @ QList<QGraphicsPixmapItem*> targetItems;
foreach(QPixmap pix, main_targets) {
QGraphicsPixmapItem* p_item = new QGraphicsPixmapItem(pix);
targetItems.append(p_item);@ fills the main_target list. If not what is the purpose of this line?

andreyc

In this code you take the pixmaps from main_target and create qlist of qgraphicsitems.
So, the main_target must be populated by the qpixmaps before this code.

DSlim

@ main_targets[0] = QPixmap(":images/darkbluelogo.jpg");
main_targets[1] = QPixmap(":images/graylogo.jpg");
main_targets[2] = QPixmap(":images/lightbluelogo.jpg");
main_targets[3] = QPixmap(":images/lime.jpg");
main_targets[4] = QPixmap(":images/pink.jpg");
main_targets[5] = QPixmap(":images/purple.jpg");
main_targets[6] = QPixmap(":images/redlogo.jpg");
main_targets[7] = QPixmap(":images/yellow.jpg");
main_targets[8] = QPixmap(":images/brown.jpg");@

The main_targets are created and stored in the constructor initially before anything is done. So the qlist should have 9 qpixmaps.

andreyc

If I'm not mistaken you need to use .append() method to add elements to the QList. QList::opeartor[] does not work for adding new elements.

EDIT: Yep, you have to use append() or operator+=() to extend a list "operator[]":http://qt-project.org/doc/qt-5/qlist.html#operator-5b-5d requires an index to be valid (0 <= i < qlist.size())

DSlim

Thank you finally have it switched over to QGraphicsPixmapItems. Now the initial problem and see if I can get the collision working.

DSlim

Ok the original problem of colliding the two objects. My thinking at the beginning of this post was to have something along the lines of:

@if(pellets->collidesWithItem(targets){
remove(pellets)
remove(targets)

}@

Asperamanca

I wouldn't delete the items right away, but only hide them, and delete them later on. But otherwise, it might be something like this.

Have you taken a look at the Colliding Mice example?

DSlim

Yeah I've looked at that example a lot. Doesn't seem to be in the realm of what I'm trying to accomplish.

Asperamanca

So you have some QGraphicsItem subclass and come QGraphicsPixmap. You check whether they collide. That part you should be able to take from the example.

If they collide, you hide those items and add them to a list of items "to be deleted" (or "to be re-used", if you prefer).

You either clean up the list from time to time (using e.g. a timer), or you re-use the items in the list if you need to add a new item (which would be a performance optimization, since creating GraphicsItems isn't free).

Where specifically do you have problems?

DSlim

The collision is comparing every item on the screen. It only removes one item not both that collide. It's not item specific.

Asperamanca

If you only want to compare two items, you can use their shape() and QPainterPath::intersects

DSlim

Is there any way to remove and delete the pellet target from within the QGraphicsRectItem. I'm just hiding the two when they collide, but that doesn't remove it and since the class inherits from the QGraphicsItem base class there isn't a removeitem() function.

@class GraphicsCircle : public QGraphicsRectItem
// class for the fire bullets
{

public:
GraphicsCircle(qreal dirx, qreal diry)
: m_Speed(5)
, m_DirX(dirx)
, m_DirY(diry)
{
setRect(-3.0,-3.0,8.0,8.0);
setPos(-140, 235);
QRadialGradient rGrad( 0.0, 0.0, 20.0, 0.0, 0.0);
rGrad.setColorAt(0.0, QColor(255,255,255));
rGrad.setColorAt(0.7, QColor(255,255,225));
rGrad.setColorAt(1.0, QColor(255,0,0,0));
setBrush(QBrush(rGrad) );
setPen(QPen(Qt::NoPen));

    w = 7;
    h = 7;
}

QRectF boundingRect() const
{
    qreal shift = 1;
        return QRectF(-w/2 -shift, - h/2
                      - shift, w + shift, h + shift);
}

QPainterPath shape() const
{
    QPainterPath path;
    path.addRect(boundingRect());
    return path;
}

virtual ~GraphicsCircle() {}

void advance(int phase)
{
    if(phase == 0) return;
    setPos(x()+m_Speed*m_DirX, y()+m_Speed*m_DirY);


    foreach( QGraphicsItem * item, this->collidingItems())
    {
         item->hide();
         this->hide();

    }

}@

Asperamanca

How about this:

@
QList<QGraphicsItem*> collisionList = this->collidingItems();
qDeleteAll(collisionList);

this->hide();
// Now it gets tricky: delete this isn't a very good idea within the context of this.
// One way to solve it: Derive the class from QObject AND QGraphicsRectItem, and use the deleteLater() call
@