source: trunk/src/gui/graphicsview/qgraphicsscenebsptreeindex.cpp@ 573

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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))