/*!
   Clears the current selection.
   
   For each item QGraphicsItem::setSelected(false) is called. Items can adjust
   selection state by responding to QGraphicsItem::ItemSelectedChange
   notification in custom implementations of QGraphicsItem::itemChange().
   Items that adjust selection state from unselected to selected are not
   removed from selection.

   \sa setSelectionArea(), selectedItems(), QGraphicsItem::itemChange()
*/
void QGraphicsScene::clearSelection()
{
    Q_D(QGraphicsScene);

    // Disable emitting selectionChanged
    ++d->selectionChanging;

    // Try to deselect selected items.
    // Note that deselection can be overridden in itemChange().
    foreach (QGraphicsItem *item, d->selectedItems) {
        item->setSelected(false);
    }

    // Count deselected items.
    int changedCount = 0;
    foreach (QGraphicsItem *item, d->selectedItems) {
        if (!item->isSelected()) {
            changedCount++;
        }
    }

    // Remove deselected items from selection list. Removing is decoupled from
    // deselecting to support complicated deselection schemes.
    if (changedCount == d->selectedItems.count()) {
        d->selectedItems.clear();
    } else if (changedCount > 0) {
        QMutableSetIterator<QGraphicsItem *> it(d->selectedItems);
        while (it.hasNext()) {
            QGraphicsItem *item = it.next();
            if (!item->isSelected()) {
                it.remove();
            }
        }
    }

    // Reenable emitting selectionChanged() for individual items.
    --d->selectionChanging;

    if (!d->selectionChanging && changedCount > 0)
        emit selectionChanged();
}