descending z order

I'd like to listing all my items in the scene whose bounding rectangle is fully contained inside the scene rect area, and i'd like to have them listed in descending z order.....
From the reference document i found:
1)

Code:

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QList<QGraphicsItem *> QGraphicsScene::items ( const QPointF & pos ) const;

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Returns all visible items at position pos in the scene. The items are listed in descending Z order

2)

Code:

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QList<QGraphicsItem *> QGraphicsScene::items ( const QRectF & rectangle, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape ) const

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Returns all visible items that, depending on mode, are either inside or intersect with the specified rectangle;

How can i obtain my behaviour???

Use the second approach by passing the scene rect and sort the returned list by QGraphicsItem::zValue.

is there any class dealing with sorting? Or i have to implement my sorting alghoritm, like quicksort or mergesort??

Use void qSort ( RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan ) . You will have to define your own lessThan function.

i have proble defining my own less than function.........

" no matching function for call to ‘qSort(QList<QGraphicsItem*>::iterator, QList<QGraphicsItem*>::iterator, <unresolved overloaded function type>)"

header:

Code:

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bool zOrderlessThan(const QGraphicsItem*,const QGraphicsItem*);

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source:

Code:

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bool myclas::zOrderlessThan(const QGraphicsItem* i1,const QGraphicsItem* i2){
	return i1->zValue() > i2->zValue();
}

---

????????

Either make it a static function or don't make it a member function at all.

making the function static, i resolve the problem of the function visibility, but i don't resolve an other problem dealing with the iterator.

I have a List: QList<QGraphicsItem*> objects and i'd like to use qsort on this list.
So i define my static function:

Code:

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static bool zOrderlessThan(QList<QGraphicsItem*>::const_iterator i1,QList<QGraphicsItem*>::const_iterator i2){
			return (*i1)->zValue() > (*i2)->zValue();}

---

and then i call it, from my source.cpp:

qsort(objects.begin(),objects.end(),zOrderlessThan );

and i obtain this error:

Quote:

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error: cannot convert ‘QList<QGraphicsItem*>::iterator’ to ‘void*’ for argument ‘1’ to ‘void qsort(void*, size_t, size_t, int (*)(const void*, const void*))’

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What's wrong???????????

Code:

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// main.cpp
#include <QtGui>
 
bool zValueGreaterThan(QGraphicsItem* item1, QGraphicsItem* item2)
{
    return item1->zValue() > item2->zValue();
}
 
int main()
{
    // some dummy items with z-values [0..3]
    QList<QGraphicsItem*> items;
    for (int i = 0; i < 3; ++i)
    {
        QGraphicsItem* item = new QGraphicsLineItem;
        item->setZValue(i);
        items += item;
    }
 
    qDebug() << "ascending order:\n" << items;
 
    qSort(items.begin(), items.end(), zValueGreaterThan);
 
    qDebug() << "descending order:\n" << items;
}

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ok..........thx very much. following your code , the problem goes away.:D

Note, sorting by Z order is not the same as sorting by stacking order. Usually stacking order is what you want :-).

http://doc.trolltech.com/4.3/qgraphi...html#setZValue

At the very least you should add that if the Z values are the same (which is very common), the pointers are compared to ensure sort stability. And Z value sorting only applies to immediate siblings, so if you want the items sorted by stacking order, your algorithm needs to compare Z values for immediate siblings of the two items' closest common ancestor :-).

Btw dreamer, the items() function that takes a QRectF also returns the items in descending Z order by default...