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/*!

    \class QGraphicsSceneBspTreeIndex

    \brief The QGraphicsSceneBspTreeIndex class provides an implementation of

    a BSP indexing algorithm for discovering items in QGraphicsScene.

    \since 4.6

    \ingroup graphicsview-api

    \internal

    QGraphicsSceneBspTreeIndex index use a BSP(Binary Space Partitioning)

    implementation to discover items quickly. This implementation is

    very efficient for static scene. It has a depth that you can set.

    The depth directly affects performance and memory usage; the latter

    growing exponentially with the depth of the tree. With an optimal tree

    depth, the index can instantly determine the locality of items, even

    for scenes with thousands or millions of items. This also greatly improves

    rendering performance.

    By default, the value is 0, in which case Qt will guess a reasonable

    default depth based on the size, location and number of items in the

    scene. If these parameters change frequently, however, you may experience

    slowdowns as the index retunes the depth internally. You can avoid

    potential slowdowns by fixating the tree depth through setting this

    property.

    The depth of the tree and the size of the scene rectangle decide the

    granularity of the scene's partitioning. The size of each scene segment is

    determined by the following algorithm:

    The BSP tree has an optimal size when each segment contains between 0 and

    10 items.

    \sa QGraphicsScene, QGraphicsView, QGraphicsSceneIndex

*/

#include <QtCore/qglobal.h>

#ifndef QT_NO_GRAPHICSVIEW

#include <private/qgraphicsscene_p.h>

#include <private/qgraphicsscenebsptreeindex_p.h>

#include <private/qgraphicssceneindex_p.h>

#include <QtCore/qmath.h>

#include <QtCore/qdebug.h>

QT_BEGIN_NAMESPACE

static inline int intmaxlog(int n)

{

    return  (n > 0 ? qMax(qCeil(qLn(qreal(n)) / qLn(qreal(2))), 5) : 0);

}

/*!

    Constructs a private scene bsp index.

*/

QGraphicsSceneBspTreeIndexPrivate::QGraphicsSceneBspTreeIndexPrivate(QGraphicsScene *scene)

    : QGraphicsSceneIndexPrivate(scene),

    bspTreeDepth(0),

    indexTimerId(0),

    restartIndexTimer(false),

    regenerateIndex(true),

    lastItemCount(0),

    purgePending(false),

    sortCacheEnabled(false),

    updatingSortCache(false)

{

}

/*!

    This method will update the BSP index by removing the items from the temporary

    unindexed list and add them in the indexedItems list. This will also

    update the growingItemsBoundingRect if needed. This will update the BSP

    implementation as well.

    \internal

*/

void QGraphicsSceneBspTreeIndexPrivate::_q_updateIndex()

{

    Q_Q(QGraphicsSceneBspTreeIndex);

    if (!indexTimerId)

        return;

    q->killTimer(indexTimerId);

    indexTimerId = 0;

    purgeRemovedItems();

     // Add unindexedItems to indexedItems

    for (int i = 0; i < unindexedItems.size(); ++i) {

        if (QGraphicsItem *item = unindexedItems.at(i)) {

            Q_ASSERT(!item->d_ptr->itemDiscovered);

            if (!freeItemIndexes.isEmpty()) {

                int freeIndex = freeItemIndexes.takeFirst();

                item->d_func()->index = freeIndex;

                indexedItems[freeIndex] = item;

            } else {

                item->d_func()->index = indexedItems.size();

                indexedItems << item;

            }

        }

    }

    // Determine whether we should regenerate the BSP tree.

    if (bspTreeDepth == 0) {

        int oldDepth = intmaxlog(lastItemCount);

        bspTreeDepth = intmaxlog(indexedItems.size());

        static const int slack = 100;

        if (bsp.leafCount() == 0 || (oldDepth != bspTreeDepth && qAbs(lastItemCount - indexedItems.size()) > slack)) {

            // ### Crude algorithm.

            regenerateIndex = true;

        }

    }

    // Regenerate the tree.

    if (regenerateIndex) {

        regenerateIndex = false;

        bsp.initialize(sceneRect, bspTreeDepth);

        unindexedItems = indexedItems;

        lastItemCount = indexedItems.size();

    }

    // Insert all unindexed items into the tree.

    for (int i = 0; i < unindexedItems.size(); ++i) {

        if (QGraphicsItem *item = unindexedItems.at(i)) {

            if (item->d_ptr->itemIsUntransformable()) {

                untransformableItems << item;

                continue;

            }

            if (item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren)

                continue;

            bsp.insertItem(item, item->d_ptr->sceneEffectiveBoundingRect());

        }

    }

    unindexedItems.clear();

}

/*!

    \internal

    Removes stale pointers from all data structures.

*/

void QGraphicsSceneBspTreeIndexPrivate::purgeRemovedItems()

{

    if (!purgePending && removedItems.isEmpty())

        return;

    // Remove stale items from the BSP tree.

    bsp.removeItems(removedItems);

    // Purge this list.

    removedItems.clear();

    freeItemIndexes.clear();

    for (int i = 0; i < indexedItems.size(); ++i) {

        if (!indexedItems.at(i))

            freeItemIndexes << i;

    }

    purgePending = false;

}

/*!

    \internal

    Starts or restarts the timer used for reindexing unindexed items.

*/

void QGraphicsSceneBspTreeIndexPrivate::startIndexTimer(int interval)

{

    Q_Q(QGraphicsSceneBspTreeIndex);

    if (indexTimerId) {

        restartIndexTimer = true;

    } else {

        indexTimerId = q->startTimer(interval);

    }

}

/*!

    \internal

*/

void QGraphicsSceneBspTreeIndexPrivate::resetIndex()

{

    purgeRemovedItems();

    for (int i = 0; i < indexedItems.size(); ++i) {

        if (QGraphicsItem *item = indexedItems.at(i)) {

            item->d_ptr->index = -1;

            Q_ASSERT(!item->d_ptr->itemDiscovered);

            unindexedItems << item;

        }

    }

    indexedItems.clear();

    freeItemIndexes.clear();

    untransformableItems.clear();

    regenerateIndex = true;

    startIndexTimer();

}

/*!

    \internal

*/

void QGraphicsSceneBspTreeIndexPrivate::climbTree(QGraphicsItem *item, int *stackingOrder)

{

    if (!item->d_ptr->children.isEmpty()) {

        QList<QGraphicsItem *> childList = item->d_ptr->children;

        qSort(childList.begin(), childList.end(), qt_closestLeaf);

        for (int i = 0; i < childList.size(); ++i) {

            QGraphicsItem *item = childList.at(i);

            if (!(item->flags() & QGraphicsItem::ItemStacksBehindParent))

                climbTree(childList.at(i), stackingOrder);

        }

        item->d_ptr->globalStackingOrder = (*stackingOrder)++;

        for (int i = 0; i < childList.size(); ++i) {

            QGraphicsItem *item = childList.at(i);

            if (item->flags() & QGraphicsItem::ItemStacksBehindParent)

                climbTree(childList.at(i), stackingOrder);

        }

    } else {

        item->d_ptr->globalStackingOrder = (*stackingOrder)++;

    }

}

/*!

    \internal

*/

void QGraphicsSceneBspTreeIndexPrivate::_q_updateSortCache()

{

    Q_Q(QGraphicsSceneBspTreeIndex);

    _q_updateIndex();

    if (!sortCacheEnabled || !updatingSortCache)

        return;

    updatingSortCache = false;

    int stackingOrder = 0;

    QList<QGraphicsItem *> topLevels;

    const QList<QGraphicsItem *> items = q->items();

    for (int i = 0; i < items.size(); ++i) {

        QGraphicsItem *item = items.at(i);

        if (item && !item->d_ptr->parent)

            topLevels << item;

    }

    qSort(topLevels.begin(), topLevels.end(), qt_closestLeaf);

    for (int i = 0; i < topLevels.size(); ++i)

        climbTree(topLevels.at(i), &stackingOrder);

}

/*!

    \internal

*/

void QGraphicsSceneBspTreeIndexPrivate::invalidateSortCache()

{

    Q_Q(QGraphicsSceneBspTreeIndex);

    if (!sortCacheEnabled || updatingSortCache)

        return;

    updatingSortCache = true;

    QMetaObject::invokeMethod(q, "_q_updateSortCache", Qt::QueuedConnection);

}

void QGraphicsSceneBspTreeIndexPrivate::addItem(QGraphicsItem *item, bool recursive)

{

    if (!item)

        return;

    // Prevent reusing a recently deleted pointer: purge all removed item from our lists.

    purgeRemovedItems();

    // Invalidate any sort caching; arrival of a new item means we need to resort.

    // Update the scene's sort cache settings.

    item->d_ptr->globalStackingOrder = -1;

    invalidateSortCache();

    // Indexing requires sceneBoundingRect(), but because \a item might

    // not be completely constructed at this point, we need to store it in

    // a temporary list and schedule an indexing for later.

    if (item->d_ptr->index == -1) {

        Q_ASSERT(!unindexedItems.contains(item));

        unindexedItems << item;

        startIndexTimer(0);

    } else {

        Q_ASSERT(indexedItems.contains(item));

        qWarning("QGraphicsSceneBspTreeIndex::addItem: item has already been added to this BSP");

    }

    if (recursive) {

        for (int i = 0; i < item->d_ptr->children.size(); ++i)

            addItem(item->d_ptr->children.at(i), recursive);

    }

}

void QGraphicsSceneBspTreeIndexPrivate::removeItem(QGraphicsItem *item, bool recursive,

                                                   bool moveToUnindexedItems)

{

    if (!item)

        return;

    if (item->d_ptr->index != -1) {

        Q_ASSERT(item->d_ptr->index < indexedItems.size());

        Q_ASSERT(indexedItems.at(item->d_ptr->index) == item);

        Q_ASSERT(!item->d_ptr->itemDiscovered);

        freeItemIndexes << item->d_ptr->index;

        indexedItems[item->d_ptr->index] = 0;

        item->d_ptr->index = -1;

        if (item->d_ptr->itemIsUntransformable()) {

            untransformableItems.removeOne(item);

        } else if (item->d_ptr->inDestructor) {

            // Avoid virtual function calls from the destructor.

            purgePending = true;

            removedItems << item;

        } else if (!(item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren)) {

            bsp.removeItem(item, item->d_ptr->sceneEffectiveBoundingRect());

        }

    } else {

        unindexedItems.removeOne(item);

    }

    invalidateSortCache(); // ### Only do this when removing from BSP?

    Q_ASSERT(item->d_ptr->index == -1);

    Q_ASSERT(!indexedItems.contains(item));

    Q_ASSERT(!unindexedItems.contains(item));

    Q_ASSERT(!untransformableItems.contains(item));

    if (moveToUnindexedItems)

        addItem(item);

    if (recursive) {

        for (int i = 0; i < item->d_ptr->children.size(); ++i)

            removeItem(item->d_ptr->children.at(i), recursive, moveToUnindexedItems);

    }

}

QList<QGraphicsItem *> QGraphicsSceneBspTreeIndexPrivate::estimateItems(const QRectF &rect, Qt::SortOrder order,

                                                                        bool onlyTopLevelItems)

{

    Q_Q(QGraphicsSceneBspTreeIndex);

    if (onlyTopLevelItems && rect.isNull())

        return q->QGraphicsSceneIndex::estimateTopLevelItems(rect, order);

    purgeRemovedItems();

    _q_updateSortCache();

    Q_ASSERT(unindexedItems.isEmpty());

    QList<QGraphicsItem *> rectItems = bsp.items(rect, onlyTopLevelItems);

    if (onlyTopLevelItems) {

        for (int i = 0; i < untransformableItems.size(); ++i) {

            QGraphicsItem *item = untransformableItems.at(i);

            if (!item->d_ptr->parent) {

                rectItems << item;

            } else {

                item = item->topLevelItem();

                if (!rectItems.contains(item))

                    rectItems << item;

            }

        }

    } else {

        rectItems += untransformableItems;

    }

    sortItems(&rectItems, order, sortCacheEnabled, onlyTopLevelItems);

    return rectItems;

}

/*!

    Sort a list of \a itemList in a specific \a order and use the cache if requested.

    \internal

*/

void QGraphicsSceneBspTreeIndexPrivate::sortItems(QList<QGraphicsItem *> *itemList, Qt::SortOrder order,

                                                  bool sortCacheEnabled, bool onlyTopLevelItems)

{

    if (order == Qt::SortOrder(-1))

        return;

    if (onlyTopLevelItems) {

        if (order == Qt::DescendingOrder)

            qSort(itemList->begin(), itemList->end(), qt_closestLeaf);

        else if (order == Qt::AscendingOrder)

            qSort(itemList->begin(), itemList->end(), qt_notclosestLeaf);

        return;

    }

    if (sortCacheEnabled) {

        if (order == Qt::DescendingOrder) {

            qSort(itemList->begin(), itemList->end(), closestItemFirst_withCache);

        } else if (order == Qt::AscendingOrder) {

            qSort(itemList->begin(), itemList->end(), closestItemLast_withCache);

        }

    } else {

        if (order == Qt::DescendingOrder) {

            qSort(itemList->begin(), itemList->end(), qt_closestItemFirst);

        } else if (order == Qt::AscendingOrder) {

            qSort(itemList->begin(), itemList->end(), qt_closestItemLast);

        }

    }

}

/*!

    Constructs a BSP scene index for the given \a scene.

*/

QGraphicsSceneBspTreeIndex::QGraphicsSceneBspTreeIndex(QGraphicsScene *scene)

    : QGraphicsSceneIndex(*new QGraphicsSceneBspTreeIndexPrivate(scene), scene)

{

}

QGraphicsSceneBspTreeIndex::~QGraphicsSceneBspTreeIndex()

{

    Q_D(QGraphicsSceneBspTreeIndex);

    for (int i = 0; i < d->indexedItems.size(); ++i) {

        // Ensure item bits are reset properly.

        if (QGraphicsItem *item = d->indexedItems.at(i)) {

            Q_ASSERT(!item->d_ptr->itemDiscovered);

            item->d_ptr->index = -1;

        }

    }

}

/*!

    \internal

    Clear the all the BSP index.

*/

void QGraphicsSceneBspTreeIndex::clear()

{

    Q_D(QGraphicsSceneBspTreeIndex);

    d->bsp.clear();

    d->lastItemCount = 0;

    d->freeItemIndexes.clear();

    for (int i = 0; i < d->indexedItems.size(); ++i) {

        // Ensure item bits are reset properly.

        if (QGraphicsItem *item = d->indexedItems.at(i)) {

            Q_ASSERT(!item->d_ptr->itemDiscovered);

            item->d_ptr->index = -1;

        }

    }

    d->indexedItems.clear();

    d->unindexedItems.clear();

    d->untransformableItems.clear();

    d->regenerateIndex = true;

}

/*!

    Add the \a item into the BSP index.

*/

void QGraphicsSceneBspTreeIndex::addItem(QGraphicsItem *item)

{

    Q_D(QGraphicsSceneBspTreeIndex);

    d->addItem(item);

}

/*!

    Remove the \a item from the BSP index.

*/

void QGraphicsSceneBspTreeIndex::removeItem(QGraphicsItem *item)

{

    Q_D(QGraphicsSceneBspTreeIndex);

    d->removeItem(item);

}

/*!

    \internal

    Update the BSP when the \a item 's bounding rect has changed.

*/

void QGraphicsSceneBspTreeIndex::prepareBoundingRectChange(const QGraphicsItem *item)

{

    if (!item)

        return;

    if (item->d_ptr->index == -1 || item->d_ptr->itemIsUntransformable()

        || (item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren)) {

        return; // Item is not in BSP tree; nothing to do.

    }

    Q_D(QGraphicsSceneBspTreeIndex);

    QGraphicsItem *thatItem = const_cast<QGraphicsItem *>(item);

    d->removeItem(thatItem, /*recursive=*/false, /*moveToUnindexedItems=*/true);

    for (int i = 0; i < item->d_ptr->children.size(); ++i)  // ### Do we really need this?

        prepareBoundingRectChange(item->d_ptr->children.at(i));

}

/*!

    Returns an estimation visible items that are either inside or

    intersect with the specified \a rect and return a list sorted using \a order.

    \a deviceTransform is the transformation apply to the view.