Qt
Internal/Contributor docs for the Qt SDK. <b>Note:</b> These are NOT official API docs; those are found <a href='https://doc.qt.io/'>here</a>.
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QGraphicsEffect Class Referenceabstract

The QGraphicsEffect class is the base class for all graphics effects. More...

#include <qgraphicseffect.h>

+ Inheritance diagram for QGraphicsEffect:
+ Collaboration diagram for QGraphicsEffect:

Public Types

enum  ChangeFlag { SourceAttached = 0x1 , SourceDetached = 0x2 , SourceBoundingRectChanged = 0x4 , SourceInvalidated = 0x8 }
 This enum describes what has changed in QGraphicsEffectSource. More...
 
enum  PixmapPadMode { NoPad , PadToTransparentBorder , PadToEffectiveBoundingRect }
 This enum describes how the pixmap returned from sourcePixmap should be padded. More...
 

Public Slots

void setEnabled (bool enable)
 
void update ()
 Schedules a redraw of the effect.
 
- Public Slots inherited from QObject
void deleteLater ()
 \threadsafe
 

Signals

void enabledChanged (bool enabled)
 This signal is emitted whenever the effect is enabled or disabled.
 
- Signals inherited from QObject
void destroyed (QObject *=nullptr)
 This signal is emitted immediately before the object obj is destroyed, after any instances of QPointer have been notified, and cannot be blocked.
 
void objectNameChanged (const QString &objectName, QPrivateSignal)
 This signal is emitted after the object's name has been changed.
 

Public Member Functions

 QGraphicsEffect (QObject *parent=nullptr)
 Constructs a new QGraphicsEffect instance having the specified parent.
 
virtual ~QGraphicsEffect ()
 Removes the effect from the source, and destroys the graphics effect.
 
virtual QRectF boundingRectFor (const QRectF &sourceRect) const
 Returns the effective bounding rectangle for this effect, given the provided rect in the device coordinates.
 
QRectF boundingRect () const
 Returns the effective bounding rectangle for this effect, i.e., the bounding rectangle of the source in device coordinates, adjusted by any margins applied by the effect itself.
 
bool isEnabled () const
 
QGraphicsEffectSourcesource () const
 
- Public Member Functions inherited from QObject
Q_INVOKABLE QObject (QObject *parent=nullptr)
 Constructs an object with parent object parent.
 
virtual ~QObject ()
 Destroys the object, deleting all its child objects.
 
virtual bool event (QEvent *event)
 This virtual function receives events to an object and should return true if the event e was recognized and processed.
 
virtual bool eventFilter (QObject *watched, QEvent *event)
 Filters events if this object has been installed as an event filter for the watched object.
 
QString objectName () const
 
Q_WEAK_OVERLOAD void setObjectName (const QString &name)
 Sets the object's name to name.
 
void setObjectName (QAnyStringView name)
 This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
 
QBindable< QStringbindableObjectName ()
 
bool isWidgetType () const
 Returns true if the object is a widget; otherwise returns false.
 
bool isWindowType () const
 Returns true if the object is a window; otherwise returns false.
 
bool isQuickItemType () const
 Returns true if the object is a QQuickItem; otherwise returns false.
 
bool signalsBlocked () const noexcept
 Returns true if signals are blocked; otherwise returns false.
 
bool blockSignals (bool b) noexcept
 If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it).
 
QThreadthread () const
 Returns the thread in which the object lives.
 
bool moveToThread (QThread *thread QT6_DECL_NEW_OVERLOAD_TAIL)
 Changes the thread affinity for this object and its children and returns true on success.
 
int startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)
 This is an overloaded function that will start a timer of type timerType and a timeout of interval milliseconds.
 
int startTimer (std::chrono::nanoseconds time, Qt::TimerType timerType=Qt::CoarseTimer)
 
void killTimer (int id)
 Kills the timer with timer identifier, id.
 
void killTimer (Qt::TimerId id)
 
template<typename T >
findChild (QAnyStringView aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
 Returns the child of this object that can be cast into type T and that is called name, or \nullptr if there is no such object.
 
template<typename T >
QList< T > findChildren (QAnyStringView aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) 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.
 
template<typename T >
findChild (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
 This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
 
template<typename T >
QList< T > findChildren (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
 This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
 
const QObjectListchildren () const
 Returns a list of child objects.
 
void setParent (QObject *parent)
 Makes the object a child of parent.
 
void installEventFilter (QObject *filterObj)
 Installs an event filter filterObj on this object.
 
void removeEventFilter (QObject *obj)
 Removes an event filter object obj from this object.
 
QMetaObject::Connection connect (const QObject *sender, const char *signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const
 
bool disconnect (const char *signal=nullptr, const QObject *receiver=nullptr, const char *member=nullptr) const
 
bool disconnect (const QObject *receiver, const char *member=nullptr) const
 
void dumpObjectTree () const
 Dumps a tree of children to the debug output.
 
void dumpObjectInfo () const
 Dumps information about signal connections, etc.
 
bool setProperty (const char *name, const QVariant &value)
 Sets the value of the object's name property to value.
 
bool setProperty (const char *name, QVariant &&value)
 
QVariant property (const char *name) const
 Returns the value of the object's name property.
 
QList< QByteArraydynamicPropertyNames () const
 
QBindingStoragebindingStorage ()
 
const QBindingStoragebindingStorage () const
 
QObjectparent () const
 Returns a pointer to the parent object.
 
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.
 

Protected Member Functions

 QGraphicsEffect (QGraphicsEffectPrivate &d, QObject *parent=nullptr)
 
virtual void draw (QPainter *painter)=0
 This pure virtual function draws the effect and is called whenever the source needs to be drawn.
 
virtual void sourceChanged (ChangeFlags flags)
 This virtual function is called by QGraphicsEffect to notify the effect that the source has changed.
 
void updateBoundingRect ()
 This function notifies the effect framework when the effect's bounding rectangle has changed.
 
bool sourceIsPixmap () const
 Returns true if the source effectively is a pixmap, e.g., a QGraphicsPixmapItem.
 
QRectF sourceBoundingRect (Qt::CoordinateSystem system=Qt::LogicalCoordinates) const
 Returns the bounding rectangle of the source mapped to the given system.
 
void drawSource (QPainter *painter)
 Draws the source directly using the given painter.
 
QPixmap sourcePixmap (Qt::CoordinateSystem system=Qt::LogicalCoordinates, QPoint *offset=nullptr, PixmapPadMode mode=PadToEffectiveBoundingRect) const
 Returns a pixmap with the source painted into it.
 
- Protected Member Functions inherited from QObject
QObjectsender () const
 Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns \nullptr.
 
int senderSignalIndex () const
 
int receivers (const char *signal) const
 Returns the number of receivers connected to the signal.
 
bool isSignalConnected (const QMetaMethod &signal) const
 
virtual void timerEvent (QTimerEvent *event)
 This event handler can be reimplemented in a subclass to receive timer events for the object.
 
virtual void childEvent (QChildEvent *event)
 This event handler can be reimplemented in a subclass to receive child events.
 
virtual void customEvent (QEvent *event)
 This event handler can be reimplemented in a subclass to receive custom events.
 
virtual void connectNotify (const QMetaMethod &signal)
 
virtual void disconnectNotify (const QMetaMethod &signal)
 
 QObject (QObjectPrivate &dd, QObject *parent=nullptr)
 

Properties

bool enabled
 whether the effect is enabled or not.
 
- Properties inherited from QObject
QString objectName
 the name of this object
 

Friends

class QGraphicsItem
 
class QGraphicsItemPrivate
 
class QGraphicsScenePrivate
 
class QWidget
 
class QWidgetPrivate
 

Additional Inherited Members

- Static Public Member Functions inherited from QObject
static QMetaObject::Connection connect (const QObject *sender, const char *signal, const QObject *receiver, const char *member, Qt::ConnectionType=Qt::AutoConnection)
 \threadsafe
 
static QMetaObject::Connection connect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)
 
template<typename Func1 , typename Func2 >
static QMetaObject::Connection connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, const typename QtPrivate::ContextTypeForFunctor< Func2 >::ContextType *context, Func2 &&slot, Qt::ConnectionType type=Qt::AutoConnection)
 
template<typename Func1 , typename Func2 >
static QMetaObject::Connection connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, Func2 &&slot)
 
static bool disconnect (const QObject *sender, const char *signal, const QObject *receiver, const char *member)
 \threadsafe
 
static bool disconnect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &member)
 
static bool disconnect (const QMetaObject::Connection &)
 Disconnect a connection.
 
template<typename Func1 , typename Func2 >
static bool disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, const typename QtPrivate::FunctionPointer< Func2 >::Object *receiver, Func2 slot)
 
template<typename Func1 >
static bool disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, const QObject *receiver, void **zero)
 
- Protected Attributes inherited from QObject
QScopedPointer< QObjectDatad_ptr
 

Detailed Description

The QGraphicsEffect class is the base class for all graphics effects.

Since
4.6

\inmodule QtWidgets

Effects alter the appearance of elements by hooking into the rendering pipeline and operating between the source (e.g., a QGraphicsPixmapItem) and the destination device (e.g., QGraphicsView's viewport). Effects can be disabled by calling setEnabled(false). If effects are disabled, the source is rendered directly.

To add a visual effect to a QGraphicsItem, for example, you can use one of the standard effects, or alternately, create your own effect by creating a subclass of QGraphicsEffect. The effect can then be installed on the item using QGraphicsItem::setGraphicsEffect().

Qt provides the following standard effects:

\list

\table \row

  • {2,1} \row
  • \row
  • \endtable

For more information on how to use each effect, refer to the specific effect's documentation.

To create your own custom effect, create a subclass of QGraphicsEffect (or any other existing effects) and reimplement the virtual function draw(). This function is called whenever the effect needs to redraw. The draw() function takes the painter with which to draw as an argument. For more information, refer to the documentation for draw(). In the draw() function you can call sourcePixmap() to get a pixmap of the graphics effect source which you can then process.

If your effect changes, use update() to request for a redraw. If your custom effect changes the bounding rectangle of the source, e.g., a radial glow effect may need to apply an extra margin, you can reimplement the virtual boundingRectFor() function, and call updateBoundingRect() to notify the framework whenever this rectangle changes. The virtual sourceChanged() function is called to notify the effects that the source has changed in some way - e.g., if the source is a QGraphicsRectItem and its rectangle parameters have changed.

See also
QGraphicsItem::setGraphicsEffect(), QWidget::setGraphicsEffect()

Definition at line 26 of file qgraphicseffect.h.

Member Enumeration Documentation

◆ ChangeFlag

This enum describes what has changed in QGraphicsEffectSource.

\value SourceAttached The effect is installed on a source. \value SourceDetached The effect is uninstalled on a source. \value SourceBoundingRectChanged The bounding rect of the source has changed. \value SourceInvalidated The visual appearance of the source has changed.

Enumerator
SourceAttached 
SourceDetached 
SourceBoundingRectChanged 
SourceInvalidated 

Definition at line 31 of file qgraphicseffect.h.

◆ PixmapPadMode

This enum describes how the pixmap returned from sourcePixmap should be padded.

\value NoPad The pixmap should not receive any additional padding. \value PadToTransparentBorder The pixmap should be padded to ensure it has a completely transparent border. \value PadToEffectiveBoundingRect The pixmap should be padded to match the effective bounding rectangle of the effect.

Enumerator
NoPad 
PadToTransparentBorder 
PadToEffectiveBoundingRect 

Definition at line 40 of file qgraphicseffect.h.

Constructor & Destructor Documentation

◆ QGraphicsEffect() [1/2]

QGraphicsEffect::QGraphicsEffect ( QObject * parent = nullptr)

Constructs a new QGraphicsEffect instance having the specified parent.

Definition at line 363 of file qgraphicseffect.cpp.

◆ ~QGraphicsEffect()

QGraphicsEffect::~QGraphicsEffect ( )
virtual

Removes the effect from the source, and destroys the graphics effect.

Definition at line 379 of file qgraphicseffect.cpp.

References d.

◆ QGraphicsEffect() [2/2]

QGraphicsEffect::QGraphicsEffect ( QGraphicsEffectPrivate & dd,
QObject * parent = nullptr )
protected

Definition at line 371 of file qgraphicseffect.cpp.

Member Function Documentation

◆ boundingRect()

QRectF QGraphicsEffect::boundingRect ( ) const

Returns the effective bounding rectangle for this effect, i.e., the bounding rectangle of the source in device coordinates, adjusted by any margins applied by the effect itself.

See also
boundingRectFor(), updateBoundingRect()

Definition at line 392 of file qgraphicseffect.cpp.

References boundingRectFor(), and d.

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◆ boundingRectFor()

QRectF QGraphicsEffect::boundingRectFor ( const QRectF & rect) const
virtual

Returns the effective bounding rectangle for this effect, given the provided rect in the device coordinates.

When writing you own custom effect, you must call updateBoundingRect() whenever any parameters are changed that may cause this this function to return a different value.

See also
sourceBoundingRect()

Reimplemented in QGraphicsBlurEffect, and QGraphicsDropShadowEffect.

Definition at line 409 of file qgraphicseffect.cpp.

References rect.

Referenced by boundingRect(), and QGraphicsItemPrivate::effectiveBoundingRect().

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◆ draw()

void QGraphicsEffect::draw ( QPainter * painter)
protectedpure virtual

This pure virtual function draws the effect and is called whenever the source needs to be drawn.

Reimplement this function in a QGraphicsEffect subclass to provide the effect's drawing implementation, using painter.

For example:

MyGraphicsEffect::draw(QPainter *painter)
{
...
if (sourceIsPixmap()) {
// No point in drawing in device coordinates (pixmap will be scaled anyways).
const QPixmap pixmap = sourcePixmap(Qt::LogicalCoordinates, &offset);
...
} else {
// Draw pixmap in device coordinates to avoid pixmap scaling;
const QPixmap pixmap = sourcePixmap(Qt::DeviceCoordinates, &offset);
...
}
...
}

This function should not be called explicitly by the user, since it is meant for reimplementation purposes only.

Implemented in QGraphicsColorizeEffect, QGraphicsBlurEffect, QGraphicsDropShadowEffect, and QGraphicsOpacityEffect.

Referenced by QGraphicsScenePrivate::drawSubtreeRecursive(), and QWidgetPrivate::drawWidget().

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◆ drawSource()

void QGraphicsEffect::drawSource ( QPainter * painter)
protected

Draws the source directly using the given painter.

This function should only be called from QGraphicsEffect::draw().

For example:

MyGraphicsOpacityEffect::draw(QPainter *painter)
{
// Fully opaque; draw directly without going through a pixmap.
if (qFuzzyCompare(m_opacity, 1)) {
drawSource(painter);
return;
}
...
}
See also
QGraphicsEffect::draw()

Definition at line 215 of file qgraphicseffect.cpp.

References d, and painter.

Referenced by QGraphicsColorizeEffect::draw(), QGraphicsBlurEffect::draw(), QGraphicsDropShadowEffect::draw(), and QGraphicsOpacityEffect::draw().

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◆ enabledChanged

void QGraphicsEffect::enabledChanged ( bool enabled)
signal

This signal is emitted whenever the effect is enabled or disabled.

The enabled parameter holds the effects's new enabled state.

See also
isEnabled()

Referenced by setEnabled().

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◆ isEnabled()

bool QGraphicsEffect::isEnabled ( ) const

Definition at line 427 of file qgraphicseffect.cpp.

References d.

Referenced by QGraphicsScenePrivate::drawSubtreeRecursive(), QWidgetPrivate::drawWidget(), QGraphicsItemPrivate::effectiveBoundingRect(), and QGraphicsItemPrivate::effectiveBoundingRect().

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◆ setEnabled

void QGraphicsEffect::setEnabled ( bool enable)
slot

Definition at line 433 of file qgraphicseffect.cpp.

References d, emit, and enabledChanged().

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◆ source()

QGraphicsEffectSource * QGraphicsEffect::source ( ) const

Returns a pointer to the source, which provides extra context information that can be useful for the effect.

See also
draw()

Definition at line 477 of file qgraphicseffect.cpp.

References d.

Referenced by QGraphicsScenePrivate::drawSubtreeRecursive(), QWidgetPrivate::drawWidget(), and sourceIsPixmap().

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◆ sourceBoundingRect()

QRectF QGraphicsEffect::sourceBoundingRect ( Qt::CoordinateSystem system = Qt::LogicalCoordinates) const
protected

Returns the bounding rectangle of the source mapped to the given system.

Calling this function with Qt::DeviceCoordinates outside of QGraphicsEffect::draw() will give undefined results, as there is no device context available.

See also
draw()

Definition at line 135 of file qgraphicseffect.cpp.

References d.

Referenced by QGraphicsOpacityEffect::draw().

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◆ sourceChanged()

void QGraphicsEffect::sourceChanged ( ChangeFlags flags)
protectedvirtual

This virtual function is called by QGraphicsEffect to notify the effect that the source has changed.

If the effect applies any cache, then this cache must be purged in order to reflect the new appearance of the source.

The flags describes what has changed.

Definition at line 552 of file qgraphicseffect.cpp.

References Q_UNUSED.

Referenced by QGraphicsScenePrivate::resetDirtyItem().

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◆ sourceIsPixmap()

bool QGraphicsEffect::sourceIsPixmap ( ) const
protected

Returns true if the source effectively is a pixmap, e.g., a QGraphicsPixmapItem.

This function is useful for optimization purposes. For instance, there's no point in drawing the source in device coordinates to avoid pixmap scaling if this function returns true - the source pixmap will be scaled anyways.

Definition at line 255 of file qgraphicseffect.cpp.

References QGraphicsEffectSource::isPixmap(), and source().

Referenced by QGraphicsColorizeEffect::draw(), and QGraphicsOpacityEffect::draw().

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◆ sourcePixmap()

QPixmap QGraphicsEffect::sourcePixmap ( Qt::CoordinateSystem system = Qt::LogicalCoordinates,
QPoint * offset = nullptr,
QGraphicsEffect::PixmapPadMode mode = PadToEffectiveBoundingRect ) const
protected

Returns a pixmap with the source painted into it.

The system specifies which coordinate system to be used for the source. The optional offset parameter returns the offset where the pixmap should be painted at using the current painter. For control on how the pixmap is padded use the mode parameter.

The returned pixmap is clipped to the current painter's device rectangle when system is Qt::DeviceCoordinates.

Calling this function with Qt::DeviceCoordinates outside of QGraphicsEffect::draw() will give undefined results, as there is no device context available.

See also
draw(), boundingRect()

Definition at line 330 of file qgraphicseffect.cpp.

References d.

Referenced by QGraphicsColorizeEffect::draw(), QGraphicsBlurEffect::draw(), QGraphicsDropShadowEffect::draw(), and QGraphicsOpacityEffect::draw().

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◆ update

void QGraphicsEffect::update ( )
slot

Schedules a redraw of the effect.

Call this function whenever the effect needs to be redrawn. This function does not trigger a redraw of the source.

See also
updateBoundingRect()

Definition at line 462 of file qgraphicseffect.cpp.

References d.

Referenced by QGraphicsColorizeEffect::setColor(), QGraphicsDropShadowEffect::setColor(), QGraphicsOpacityEffect::setOpacity(), QGraphicsOpacityEffect::setOpacityMask(), and QGraphicsColorizeEffect::setStrength().

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◆ updateBoundingRect()

void QGraphicsEffect::updateBoundingRect ( )
protected

This function notifies the effect framework when the effect's bounding rectangle has changed.

As a custom effect author, you must call this function whenever you change any parameters that will cause the virtual boundingRectFor() function to return a different value.

This function will call update() if this is necessary.

See also
boundingRectFor(), boundingRect(), sourceBoundingRect()

Definition at line 493 of file qgraphicseffect.cpp.

References d, and QGraphicsEffectSourcePrivate::EffectRectChanged.

Referenced by QGraphicsBlurEffect::setBlurRadius(), QGraphicsDropShadowEffect::setBlurRadius(), and QGraphicsDropShadowEffect::setOffset().

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Friends And Related Symbol Documentation

◆ QGraphicsItem

friend class QGraphicsItem
friend

Definition at line 77 of file qgraphicseffect.h.

◆ QGraphicsItemPrivate

friend class QGraphicsItemPrivate
friend

Definition at line 78 of file qgraphicseffect.h.

◆ QGraphicsScenePrivate

friend class QGraphicsScenePrivate
friend

Definition at line 79 of file qgraphicseffect.h.

◆ QWidget

friend class QWidget
friend

Definition at line 80 of file qgraphicseffect.h.

◆ QWidgetPrivate

friend class QWidgetPrivate
friend

Definition at line 81 of file qgraphicseffect.h.

Property Documentation

◆ enabled

QGraphicsEffect::enabled
readwrite

whether the effect is enabled or not.

If an effect is disabled, the source will be rendered with as normal, with no interference from the effect. If the effect is enabled, the source will be rendered with the effect applied.

This property is enabled by default.

Using this property, you can disable certain effects on slow platforms, in order to ensure that the user interface is responsive.

Definition at line 29 of file qgraphicseffect.h.


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