QGraphicsSceneBspTreeIndex Class Reference

The QGraphicsSceneBspTreeIndex class provides an implementation of a BSP indexing algorithm for discovering items in QGraphicsScene. More...

#include <qgraphicsscenebsptreeindex_p.h>

Inheritance diagram for QGraphicsSceneBspTreeIndex:

Public Functions
int	bspTreeDepth ()
QList< QGraphicsItem * >	estimateItems (const QRectF &rect, Qt::SortOrder order) const
	Returns an estimation visible items that are either inside or intersect with the specified rect and return a list sorted using order. More...
QList< QGraphicsItem * >	estimateTopLevelItems (const QRectF &rect, Qt::SortOrder order) const
QList< QGraphicsItem * >	items (Qt::SortOrder order=Qt::DescendingOrder) const
	Return all items in the BSP index and sort them using order. More...
	QGraphicsSceneBspTreeIndex (QGraphicsScene *scene=0)
	Constructs a BSP scene index for the given scene. More...
void	setBspTreeDepth (int depth)
	~QGraphicsSceneBspTreeIndex ()
Public Functions inherited from QGraphicsSceneIndex
virtual QList< QGraphicsItem * >	estimateItems (const QPointF &point, Qt::SortOrder order) const
	This virtual function return an estimation of items at position point. More...
virtual QList< QGraphicsItem * >	items (const QPointF &pos, Qt::ItemSelectionMode mode, Qt::SortOrder order, const QTransform &deviceTransform=QTransform()) const
	Returns all visible items that, depending on mode, are at the specified pos and return a list sorted using order. More...
virtual QList< QGraphicsItem * >	items (const QRectF &rect, Qt::ItemSelectionMode mode, Qt::SortOrder order, const QTransform &deviceTransform=QTransform()) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.Returns all visible items that, depending on mode, are either inside or intersect with the specified rect and return a list sorted using order. More...
virtual QList< QGraphicsItem * >	items (const QPolygonF &polygon, Qt::ItemSelectionMode mode, Qt::SortOrder order, const QTransform &deviceTransform=QTransform()) const
virtual QList< QGraphicsItem * >	items (const QPainterPath &path, Qt::ItemSelectionMode mode, Qt::SortOrder order, const QTransform &deviceTransform=QTransform()) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.Returns all visible items that, depending on mode, are either inside or intersect with the specified path and return a list sorted using order. More...
	QGraphicsSceneIndex (QGraphicsScene *scene=0)
	Constructs an abstract scene index for a given scene. More...
QGraphicsScene *	scene () const
	Returns the scene of this index. More...
virtual	~QGraphicsSceneIndex ()
	Destroys the scene index. More...
Public Functions inherited from QObject
bool	blockSignals (bool b)
	If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it). More...
const QObjectList &	children () const
	Returns a list of child objects. More...
bool	connect (const QObject *sender, const char *signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const
bool	disconnect (const char *signal=0, const QObject *receiver=0, const char *member=0)
bool	disconnect (const QObject *receiver, const char *member=0)
void	dumpObjectInfo ()
	Dumps information about signal connections, etc. More...
void	dumpObjectTree ()
	Dumps a tree of children to the debug output. More...
QList< QByteArray >	dynamicPropertyNames () const
	Returns the names of all properties that were dynamically added to the object using setProperty(). More...
virtual bool	eventFilter (QObject *, QEvent *)
	Filters events if this object has been installed as an event filter for the watched object. More...
template<typename T >
T	findChild (const QString &aName=QString()) const
	Returns the child of this object that can be cast into type T and that is called name, or 0 if there is no such object. More...
template<typename T >
QList< T >	findChildren (const QString &aName=QString()) const
	Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects. More...
template<typename T >
QList< T >	findChildren (const QRegExp &re) const
bool	inherits (const char *classname) const
	Returns true if this object is an instance of a class that inherits className or a QObject subclass that inherits className; otherwise returns false. More...
void	installEventFilter (QObject *)
	Installs an event filter filterObj on this object. More...
bool	isWidgetType () const
	Returns true if the object is a widget; otherwise returns false. More...
void	killTimer (int id)
	Kills the timer with timer identifier, id. More...
virtual const QMetaObject *	metaObject () const
	Returns a pointer to the meta-object of this object. More...
void	moveToThread (QThread *thread)
	Changes the thread affinity for this object and its children. More...
QString	objectName () const
QObject *	parent () const
	Returns a pointer to the parent object. More...
QVariant	property (const char *name) const
	Returns the value of the object's name property. More...
Q_INVOKABLE	QObject (QObject *parent=0)
	Constructs an object with parent object parent. More...
void	removeEventFilter (QObject *)
	Removes an event filter object obj from this object. More...
void	setObjectName (const QString &name)
void	setParent (QObject *)
	Makes the object a child of parent. More...
bool	setProperty (const char *name, const QVariant &value)
	Sets the value of the object's name property to value. More...
void	setUserData (uint id, QObjectUserData *data)
bool	signalsBlocked () const
	Returns true if signals are blocked; otherwise returns false. More...
int	startTimer (int interval)
	Starts a timer and returns a timer identifier, or returns zero if it could not start a timer. More...
QThread *	thread () const
	Returns the thread in which the object lives. More...
QObjectUserData *	userData (uint id) const
virtual	~QObject ()
	Destroys the object, deleting all its child objects. More...

Protected Slots
void	updateSceneRect (const QRectF &rect)
	This method react to the rect change of the scene and reset the BSP tree index. More...
Protected Slots inherited from QGraphicsSceneIndex
virtual void	updateSceneRect (const QRectF &rect)
	Notifies the index that the scene's scene rect has changed. More...

Protected Functions
void	addItem (QGraphicsItem *item)
	Add the item into the BSP index. More...
void	clear ()
	Clear the all the BSP index. More...
bool	event (QEvent *event)
	Used to catch the timer event. More...
void	itemChange (const QGraphicsItem *item, QGraphicsItem::GraphicsItemChange change, const void *const value)
	This method react to the change of the item and use the value to update the BSP tree if necessary. More...
void	prepareBoundingRectChange (const QGraphicsItem *item)
	Update the BSP when the item 's bounding rect has changed. More...
void	removeItem (QGraphicsItem *item)
	Remove the item from the BSP index. More...
Protected Functions inherited from QGraphicsSceneIndex
virtual void	deleteItem (QGraphicsItem *item)
	This method is called when an item has been deleted. More...
	QGraphicsSceneIndex (QGraphicsSceneIndexPrivate &dd, QGraphicsScene *scene)
Protected Functions inherited from QObject
virtual void	childEvent (QChildEvent *)
	This event handler can be reimplemented in a subclass to receive child events. More...
virtual void	connectNotify (const char *signal)
	This virtual function is called when something has been connected to signal in this object. More...
virtual void	customEvent (QEvent *)
	This event handler can be reimplemented in a subclass to receive custom events. More...
virtual void	disconnectNotify (const char *signal)
	This virtual function is called when something has been disconnected from signal in this object. More...
	QObject (QObjectPrivate &dd, QObject *parent=0)
int	receivers (const char *signal) const
	Returns the number of receivers connected to the signal. More...
QObject *	sender () const
	Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns 0. More...
int	senderSignalIndex () const
virtual void	timerEvent (QTimerEvent *)
	This event handler can be reimplemented in a subclass to receive timer events for the object. More...

Properties
int	bspTreeDepth
	the depth of the BSP index tree More...

Friends
class	QGraphicsScene
class	QGraphicsScenePrivate

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()
	Schedules this object for deletion. More...
Signals inherited from QObject
void	destroyed (QObject *=0)
	This signal is emitted immediately before the object obj is destroyed, and can not be blocked. More...
Static Public Functions inherited from QObject
static bool	connect (const QObject *sender, const char *signal, const QObject *receiver, const char *member, Qt::ConnectionType=Qt::AutoConnection)
	Creates a connection of the given type from the signal in the sender object to the method in the receiver object. More...
static bool	connect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)
static bool	disconnect (const QObject *sender, const char *signal, const QObject *receiver, const char *member)
	Disconnects signal in object sender from method in object receiver. More...
static bool	disconnect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &member)
static uint	registerUserData ()
static QString	tr (const char *sourceText, const char *comment=0, int n=-1)
static QString	trUtf8 (const char *sourceText, const char *comment=0, int n=-1)
Static Public Variables inherited from QObject
static const QMetaObject	staticMetaObject
	This variable stores the meta-object for the class. More...
Protected Variables inherited from QObject
QScopedPointer< QObjectData >	d_ptr
Static Protected Variables inherited from QObject
static const QMetaObject	staticQtMetaObject
Related Functions inherited from QObject
T	qFindChildqFindChildren (const QObject *obj, const QString &name)()
QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()
QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QRegExp &regExp)()
T *	qobject_cast (QObject *object)
	QObjectList
void *	qt_find_obj_child (QObject *parent, const char *type, const QString &name)
	Returns a pointer to the object named name that inherits type and with a given parent. More...

Detailed Description

The QGraphicsSceneBspTreeIndex class provides an implementation of a BSP indexing algorithm for discovering items in QGraphicsScene.

Since

4.6

Warning

This function is not part of the public interface.

QGraphicsSceneBspTreeIndex index use a BSP(Binary Space Partitioning) implementation to discover items quickly. This implementation is very efficient for static scenes. 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 depth 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.

See also

QGraphicsScene, QGraphicsView, QGraphicsSceneIndex

Definition at line 74 of file qgraphicsscenebsptreeindex_p.h.

Constructors and Destructors

QGraphicsSceneBspTreeIndex()

QGraphicsSceneBspTreeIndex::QGraphicsSceneBspTreeIndex

(

QGraphicsScene *

scene = 0

)

Constructs a BSP scene index for the given scene.

Definition at line 453 of file qgraphicsscenebsptreeindex.cpp.

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

}

~QGraphicsSceneBspTreeIndex()

QGraphicsSceneBspTreeIndex::~QGraphicsSceneBspTreeIndex

(

)

Definition at line 459 of file qgraphicsscenebsptreeindex.cpp.

{
    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;
        }
    }
}

Functions

addItem()

void QGraphicsSceneBspTreeIndex::addItem ( QGraphicsItem *  item )

protectedvirtual

Add the item into the BSP index.

Implements QGraphicsSceneIndex.

Definition at line 500 of file qgraphicsscenebsptreeindex.cpp.

{
    Q_D(QGraphicsSceneBspTreeIndex);
    d->addItem(item);
}

bspTreeDepth()

int QGraphicsSceneBspTreeIndex::bspTreeDepth

(

)

Referenced by items().

clear()

void QGraphicsSceneBspTreeIndex::clear ( )

protectedvirtual

Clear the all the BSP index.

Warning

This function is not part of the public interface.

Reimplemented from QGraphicsSceneIndex.

Definition at line 478 of file qgraphicsscenebsptreeindex.cpp.

{
    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;
}

estimateItems()

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

virtual

Returns an estimation visible items that are either inside or intersect with the specified rect and return a list sorted using order.

deviceTransform is the transformation apply to the view.

Implements QGraphicsSceneIndex.

Definition at line 546 of file qgraphicsscenebsptreeindex.cpp.

Referenced by estimateTopLevelItems().

{
    Q_D(const QGraphicsSceneBspTreeIndex);
    return const_cast<QGraphicsSceneBspTreeIndexPrivate*>(d)->estimateItems(rect, order);
}

estimateTopLevelItems()

QList< QGraphicsItem * > QGraphicsSceneBspTreeIndex::estimateTopLevelItems ( const QRectF &  rect, Qt::SortOrder  order  ) const

virtual

Reimplemented from QGraphicsSceneIndex.

Definition at line 552 of file qgraphicsscenebsptreeindex.cpp.

{
    Q_D(const QGraphicsSceneBspTreeIndex);
    return const_cast<QGraphicsSceneBspTreeIndexPrivate*>(d)->estimateItems(rect, order, /*onlyTopLevels=*/true);
}

event()

bool QGraphicsSceneBspTreeIndex::event ( QEvent *  event )

protectedvirtual

Used to catch the timer event.

Reimplemented Function

Warning

This function is not part of the public interface.

Reimplemented from QObject.

Definition at line 721 of file qgraphicsscenebsptreeindex.cpp.

{
    Q_D(QGraphicsSceneBspTreeIndex);
    switch (event->type()) {
    case QEvent::Timer:
            if (d->indexTimerId && static_cast<QTimerEvent *>(event)->timerId() == d->indexTimerId) {
                if (d->restartIndexTimer) {
                    d->restartIndexTimer = false;
                } else {
                    // this call will kill the timer
                    d->_q_updateIndex();
                }
            }
     // Fallthrough intended - support timers in subclasses.
    default:
        return QObject::event(event);
    }
    return true;
}

itemChange()

void QGraphicsSceneBspTreeIndex::itemChange ( const QGraphicsItem *  item, QGraphicsItem::GraphicsItemChange  change, const void *const  value  )

protectedvirtual

This method react to the change of the item and use the value to update the BSP tree if necessary.

Warning

This function is not part of the public interface.

Reimplemented from QGraphicsSceneIndex.

Definition at line 662 of file qgraphicsscenebsptreeindex.cpp.

{
    Q_D(QGraphicsSceneBspTreeIndex);
    switch (change) {
    case QGraphicsItem::ItemFlagsChange: {
        // Handle ItemIgnoresTransformations
        QGraphicsItem::GraphicsItemFlags newFlags = *static_cast<const QGraphicsItem::GraphicsItemFlags *>(value);
        bool ignoredTransform = item->d_ptr->flags & QGraphicsItem::ItemIgnoresTransformations;
        bool willIgnoreTransform = newFlags & QGraphicsItem::ItemIgnoresTransformations;
        bool clipsChildren = item->d_ptr->flags & QGraphicsItem::ItemClipsChildrenToShape;
        bool willClipChildren = newFlags & QGraphicsItem::ItemClipsChildrenToShape;
        if ((ignoredTransform != willIgnoreTransform) || (clipsChildren != willClipChildren)) {
            QGraphicsItem *thatItem = const_cast<QGraphicsItem *>(item);
            // Remove item and its descendants from the index and append
            // them to the list of unindexed items. Then, when the index
            // is updated, they will be put into the bsp-tree or the list
            // of untransformable items.
            d->removeItem(thatItem, /*recursive=*/true, /*moveToUnidexedItems=*/true);
        }
        break;
    }
    case QGraphicsItem::ItemZValueChange:
        d->invalidateSortCache();
        break;
    case QGraphicsItem::ItemParentChange: {
        d->invalidateSortCache();
        // Handle ItemIgnoresTransformations
        const QGraphicsItem *newParent = static_cast<const QGraphicsItem *>(value);
        bool ignoredTransform = item->d_ptr->itemIsUntransformable();
        bool willIgnoreTransform = (item->d_ptr->flags & QGraphicsItem::ItemIgnoresTransformations)
                                   || (newParent && newParent->d_ptr->itemIsUntransformable());
        bool ancestorClippedChildren = item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren;
        bool ancestorWillClipChildren = newParent
                            && ((newParent->d_ptr->flags & QGraphicsItem::ItemClipsChildrenToShape)
                                || (newParent->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren));
        if ((ignoredTransform != willIgnoreTransform) || (ancestorClippedChildren != ancestorWillClipChildren)) {
            QGraphicsItem *thatItem = const_cast<QGraphicsItem *>(item);
            // Remove item and its descendants from the index and append
            // them to the list of unindexed items. Then, when the index
            // is updated, they will be put into the bsp-tree or the list
            // of untransformable items.
            d->removeItem(thatItem, /*recursive=*/true, /*moveToUnidexedItems=*/true);
        }
        break;
    }
    default:
        break;
    }
}

items()

QList< QGraphicsItem * > QGraphicsSceneBspTreeIndex::items ( Qt::SortOrder  order = Qt::DescendingOrder ) const

virtual

Return all items in the BSP index and sort them using order.

Implements QGraphicsSceneIndex.

Definition at line 563 of file qgraphicsscenebsptreeindex.cpp.

{
    Q_D(const QGraphicsSceneBspTreeIndex);
    const_cast<QGraphicsSceneBspTreeIndexPrivate*>(d)->purgeRemovedItems();
    QList<QGraphicsItem *> itemList;

    // If freeItemIndexes is empty, we know there are no holes in indexedItems and
    // unindexedItems.
    if (d->freeItemIndexes.isEmpty()) {
        if (d->unindexedItems.isEmpty()) {
            itemList = d->indexedItems;
        } else {
            itemList = d->indexedItems + d->unindexedItems;
        }
    } else {
        // Rebuild the list of items to avoid holes. ### We could also just
        // compress the item lists at this point.
        foreach (QGraphicsItem *item, d->indexedItems + d->unindexedItems) {
            if (item)
                itemList << item;
        }
    }
    if (order != -1) {
        //We sort descending order
        d->sortItems(&itemList, order, d->sortCacheEnabled);
    }
    return itemList;
}

prepareBoundingRectChange()

void QGraphicsSceneBspTreeIndex::prepareBoundingRectChange ( const QGraphicsItem *  item )

protectedvirtual

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

Warning

This function is not part of the public interface.

Reimplemented from QGraphicsSceneIndex.

Definition at line 522 of file qgraphicsscenebsptreeindex.cpp.

{
    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));
}

removeItem()

void QGraphicsSceneBspTreeIndex::removeItem ( QGraphicsItem *  item )

protectedvirtual

Remove the item from the BSP index.

Implements QGraphicsSceneIndex.

Definition at line 509 of file qgraphicsscenebsptreeindex.cpp.

{
    Q_D(QGraphicsSceneBspTreeIndex);
    d->removeItem(item);
}

setBspTreeDepth()

void QGraphicsSceneBspTreeIndex::setBspTreeDepth

(

int

depth

)

Definition at line 628 of file qgraphicsscenebsptreeindex.cpp.

Referenced by QGraphicsScene::setBspTreeDepth().

{
    Q_D(QGraphicsSceneBspTreeIndex);
    if (d->bspTreeDepth == depth)
        return;
    d->bspTreeDepth = depth;
    d->resetIndex();
}

updateSceneRect

void QGraphicsSceneBspTreeIndex::updateSceneRect ( const QRectF &  rect )

protectedslot

This method react to the rect change of the scene and reset the BSP tree index.

Warning

This function is not part of the public interface.

Definition at line 646 of file qgraphicsscenebsptreeindex.cpp.

{
    Q_D(QGraphicsSceneBspTreeIndex);
    d->sceneRect = rect;
    d->resetIndex();
}

Friends and Related Functions

QGraphicsScene

friend class QGraphicsScene

friend

Definition at line 108 of file qgraphicsscenebsptreeindex_p.h.

QGraphicsScenePrivate

friend class QGraphicsScenePrivate

friend

Definition at line 109 of file qgraphicsscenebsptreeindex_p.h.

Properties

bspTreeDepth

int QGraphicsSceneBspTreeIndex::bspTreeDepth

private

the depth of the BSP index tree

Since

4.6

This value determines the depth of BSP tree. 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.

Definition at line 77 of file qgraphicsscenebsptreeindex_p.h.

Referenced by QGraphicsScene::setItemIndexMethod().

---

The documentation for this class was generated from the following files:

• /src/gui/graphicsview/qgraphicsscenebsptreeindex_p.h
• /src/gui/graphicsview/qgraphicsscenebsptreeindex.cpp