The QQuickRenderControl class provides a mechanism for rendering the Qt Quick scenegraph onto an offscreen render target in a fully application-controlled manner. More...

#include <qquickrendercontrol.h>

Inheritance diagram for QQuickRenderControl:

Collaboration diagram for QQuickRenderControl:

Signals
void	renderRequested ()
	This signal is emitted when the scene graph needs to be rendered.

void	sceneChanged ()
	This signal is emitted when the scene graph is updated, meaning that polishItems() and sync() needs to be called.

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
	QQuickRenderControl (QObject *parent=nullptr)
	Constructs a QQuickRenderControl object, with parent object parent.

	~QQuickRenderControl () override
	Destroys the instance.

void	prepareThread (QThread *targetThread)
	Prepares rendering the Qt Quick scene outside the GUI thread.

void	setSamples (int sampleCount)
	Sets the number of samples to use for multisampling.

int	samples () const

bool	initialize ()
	Initializes the scene graph resources.

void	invalidate ()
	Stop rendering and release resources.

void	beginFrame ()
	Specifies the start of a graphics frame.

void	endFrame ()
	Specifies the end of a graphics frame.

void	polishItems ()
	This function should be called as late as possible before sync().

bool	sync ()
	This function is used to synchronize the QML scene with the rendering scene graph.

void	render ()
	Renders the scenegraph using the current context.

virtual QWindow *	renderWindow (QPoint *offset)
	Reimplemented in subclasses to return the real window this render control is rendering into.

QQuickWindow *	window () const

QRhi *	rhi () const

QRhiCommandBuffer *	commandBuffer () 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< QString >	bindableObjectName ()

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).

QThread *	thread () 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 >
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 >
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 QObjectList &	children () 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< QByteArray >	dynamicPropertyNames () const

QBindingStorage *	bindingStorage ()

const QBindingStorage *	bindingStorage () const

QObject *	parent () 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`.

Static Public Member Functions
static QWindow *	renderWindowFor (QQuickWindow win, QPoint offset=nullptr)
	Returns the real window that win is being rendered to, if any.

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 Member Functions
	QQuickRenderControl (QQuickRenderControlPrivate &dd, QObject *parent=nullptr)

Protected Member Functions inherited from QObject
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 \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)

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()
	\threadsafe

Protected Attributes inherited from QObject
QScopedPointer< QObjectData >	d_ptr

Properties inherited from QObject
QString	objectName
	the name of this object

Related Symbols inherited from QObject
template< class T > T	qobject_cast (const QObject *object)
	Returns the given object cast to type T if the object is of type T (or of a subclass); otherwise returns \nullptr.

template< typename T > T	qFindChildqFindChildren (const QObject *obj, const QString &name)()

template< typename T > QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()

	QObjectList
	\macro Q_CLASSINFO(Name, Value)

Detailed Description

The QQuickRenderControl class provides a mechanism for rendering the Qt Quick scenegraph onto an offscreen render target in a fully application-controlled manner.

Since: 5.4

QQuickWindow and QQuickView and their associated internal render loops render the Qt Quick scene onto a native window. In some cases, for example when integrating with 3rd party OpenGL, Vulkan, Metal, or Direct 3D renderers, it can be useful to get the scene into a texture that can then be used in arbitrary ways by the external rendering engine. Such a mechanism is also essential when integrating with a VR framework. QQuickRenderControl makes this possible in a hardware accelerated manner, unlike the performance-wise limited alternative of using QQuickWindow::grabWindow()

When using a QQuickRenderControl, the QQuickWindow must not be \l{QWindow::show()}{shown} (it will not be visible on-screen) and there will not be an underlying native window for it. Instead, the QQuickWindow instance is associated with the render control object, using the overload of the QQuickWindow constructor, and a texture or image object specified via QQuickWindow::setRenderTarget(). The QQuickWindow object is still essential, because it represents the Qt Quick scene and provides the bulk of the scene management and event delivery mechanisms. It does not however act as a real on-screen window from the windowing system's perspective.

Management of the graphics devices, contexts, image and texture objects is up to the application. The device or context that will be used by Qt Quick must be created before calling initialize(). The creation of the texture object can be deferred, see below. Qt 5.4 introduces the ability for QOpenGLContext to adopt existing native contexts. Together with QQuickRenderControl this makes it possible to create a QOpenGLContext that shares with an external rendering engine's existing context. This new QOpenGLContext can then be used to render the Qt Quick scene into a texture that is accessible by the other engine's context too. For Vulkan, Metal, and Direct 3D there are no Qt-provided wrappers for device objects, so existing ones can be passed as-is via QQuickWindow::setGraphicsDevice().

Loading and instantiation of the QML components happen by using a QQmlEngine. Once the root object is created, it will need to be parented to the QQuickWindow's contentItem().

Applications will usually have to connect to 4 important signals:

\list

QQuickWindow::sceneGraphInitialized() Emitted at some point after calling QQuickRenderControl::initialize(). Upon this signal, the application is expected to create its framebuffer object and associate it with the QQuickWindow.

QQuickWindow::sceneGraphInvalidated() When the scenegraph resources are released, the framebuffer object can be destroyed too.

QQuickRenderControl::renderRequested() Indicates that the scene has to be rendered by calling render(). After making the context current, applications are expected to call render().

QQuickRenderControl::sceneChanged() Indicates that the scene has changed meaning that, before rendering, polishing and synchronizing is also necessary.

\endlist

To send events, for example mouse or keyboard events, to the scene, use QCoreApplication::sendEvent() with the QQuickWindow instance as the receiver.

For key events it may be also necessary to set the focus manually on the desired item. In practice this involves calling \l{QQuickItem::forceActiveFocus()}{forceActiveFocus()} on the desired item, for example the scene's root item, once it is associated with the scene (the QQuickWindow).

Note: In general QQuickRenderControl is supported in combination with all Qt Quick backends. However, some functionality, in particular grab(), may not be available in all cases.

\inmodule QtQuick

Definition at line 20 of file qquickrendercontrol.h.

Constructor & Destructor Documentation

◆ QQuickRenderControl() [1/2]

QQuickRenderControl::QQuickRenderControl ( QObject * parent = nullptr )

explicit

Constructs a QQuickRenderControl object, with parent object parent.

Definition at line 144 of file qquickrendercontrol.cpp.

◆ ~QQuickRenderControl()

QQuickRenderControl::~QQuickRenderControl ( )

override

Destroys the instance.

Releases all scenegraph resources.

See also: invalidate()

Definition at line 162 of file qquickrendercontrol.cpp.

◆ QQuickRenderControl() [2/2]

QQuickRenderControl::QQuickRenderControl	(	QQuickRenderControlPrivate &	dd,
		QObject *	parent = nullptr )

explicitprotected

Definition at line 152 of file qquickrendercontrol.cpp.

Member Function Documentation

◆ beginFrame()

void QQuickRenderControl::beginFrame ( )

Specifies the start of a graphics frame.

Calls to sync() or render() must be enclosed by calls to beginFrame() and endFrame().

Unlike the earlier OpenGL-only world of Qt 5, rendering with other graphics APIs requires more well-defined points of starting and ending a frame. When manually driving the rendering loop via QQuickRenderControl, it now falls to the user of QQuickRenderControl to specify these points.

A typical update step, including initialization of rendering into an existing texture, could look like the following. The example snippet assumes Direct3D 11 but the same concepts apply other graphics APIs as well.

if (!m_quickInitialized) {
    m_quickWindow->setGraphicsDevice(QQuickGraphicsDevice::fromDeviceAndContext(m_engine->device(), m_engine->context()));
 
    if (!m_renderControl->initialize())
        qWarning("Failed to initialize redirected Qt Quick rendering");
 
    m_quickWindow->setRenderTarget(QQuickRenderTarget::fromNativeTexture({ quint64(m_res.texture), 0 },
                                                                         QSize(QML_WIDTH, QML_HEIGHT),
                                                                         SAMPLE_COUNT));
 
    m_quickInitialized = true;
}
 
m_renderControl->polishItems();
 
m_renderControl->beginFrame();
m_renderControl->sync();
m_renderControl->render();
m_renderControl->endFrame(); // Qt Quick's rendering commands are submitted to the device context here

Note: This function does not need to be, and must not be, called when using the software adaptation of Qt Quick.; Internally beginFrame() and endFrame() invoke \l{QRhi::}{beginOffscreenFrame()} and \l{QRhi::}{endOffscreenFrame()}, respectively. This implies that there must not be a frame (neither offscreen, nor swapchain-based) being recorded on the QRhi when this function is called.

Since: 6.0

See also: endFrame(), initialize(), sync(), render(), QQuickGraphicsDevice, QQuickRenderTarget

Definition at line 685 of file qquickrendercontrol.cpp.

◆ commandBuffer()

QRhiCommandBuffer * QQuickRenderControl::commandBuffer ( ) const

Returns: the current command buffer.

Once beginFrame() is called, a QRhiCommandBuffer is set up automatically. That is the command buffer Qt Quick scenegraph uses, but in some cases applications may also want to query it, for example to issue resource updates (for example, a texture readback).

The returned command buffer reference should only be used between beginFrame() and endFrame(). There are specific exceptions, for example calling \l{QRhiCommandBuffer::lastCompletedGpuTime()}{lastCompletedGpuTime()} on the command buffer right after endFrame(), but before the next beginFrame(), is valid.

Note: This function is not applicable and returns null when using the software adaptation of Qt Quick.

Since: 6.6

See also: rhi(), beginFrame(), endFrame()

Definition at line 630 of file qquickrendercontrol.cpp.

◆ endFrame()

void QQuickRenderControl::endFrame ( )

Specifies the end of a graphics frame.

Calls to sync() or render() must be enclosed by calls to beginFrame() and endFrame().

When this function is called, any graphics commands enqueued by the scenegraph are submitted to the context or command queue, whichever is applicable.

Note: This function does not need to be, and must not be, called when using the software adaptation of Qt Quick.

Since: 6.0

See also: beginFrame(), initialize(), sync(), render(), QQuickGraphicsDevice, QQuickRenderTarget

Definition at line 737 of file qquickrendercontrol.cpp.

◆ initialize()

bool QQuickRenderControl::initialize ( )

Initializes the scene graph resources.

When using a graphics API, such as Vulkan, Metal, OpenGL, or Direct3D, for Qt Quick rendering, QQuickRenderControl will set up an appropriate rendering engine when this function is called. This rendering infrastructure exists as long as the QQuickRenderControl exists.

To control what graphics API Qt Quick uses, call QQuickWindow::setGraphicsApi() with one of the QSGRendererInterface:GraphicsApi constants. That must be done before calling this function.

To prevent the scenegraph from creating its own device and context objects, specify an appropriate QQuickGraphicsDevice, wrapping existing graphics objects, by calling QQuickWindow::setGraphicsDevice().

To configure which device extensions to enable (for example, for Vulkan), call QQuickWindow::setGraphicsConfiguration() before this function.

Note: When using Vulkan, QQuickRenderControl does not create a QVulkanInstance automatically. Rather, it is the application's responsibility to create a suitable QVulkanInstance and \l{QWindow::setVulkanInstance()}{associate it} with the QQuickWindow. Before initializing the QVulkanInstance, it is strongly encouraged to query the list of Qt Quick's desired instance extensions by calling the static function QQuickGraphicsConfiguration::preferredInstanceExtensions() and to pass the returned list to QVulkanInstance::setExtensions().

Returns true on success, false otherwise.

Note: This function does not need to be, and must not be, called when using the software adaptation of Qt Quick.

With the default Qt Quick adaptation this function creates a new \l QRhi object, similarly to what would happen with an on-screen QQuickWindow when QQuickRenderControl was not used. To make this new QRhi object adopt some existing device or context resource (e.g. use an existing QOpenGLContext instead of creating a new one), use QQuickWindow::setGraphicsDevice() as mentioned above. When the application wants to make the Qt Quick rendering use an already existing \l QRhi object, that is possible as well via \l QQuickGraphicsDevice::fromRhi(). When such a QQuickGraphicsDevice, referencing an already existing QRhi, is set, there will be no new, dedicated \l QRhi object created in initialize().

Since: 6.0

See also: QQuickRenderTarget, QQuickGraphicsDevice, QQuickGraphicsConfiguration::preferredInstanceExtensions()

Definition at line 299 of file qquickrendercontrol.cpp.

◆ invalidate()

void QQuickRenderControl::invalidate ( )

Stop rendering and release resources.

This is the equivalent of the cleanup operations that happen with a real QQuickWindow when the window becomes hidden.

This function is called from the destructor. Therefore there will typically be no need to call it directly.

Once invalidate() has been called, it is possible to reuse the QQuickRenderControl instance by calling initialize() again.

Note: This function does not take QQuickWindow::persistentSceneGraph() or QQuickWindow::persistentGraphics() into account. This means that context-specific resources are always released.

Definition at line 401 of file qquickrendercontrol.cpp.

◆ polishItems()

void QQuickRenderControl::polishItems ( )

This function should be called as late as possible before sync().

In a threaded scenario, rendering can happen in parallel with this function.

Definition at line 334 of file qquickrendercontrol.cpp.

◆ prepareThread()

void QQuickRenderControl::prepareThread ( QThread * targetThread )

Prepares rendering the Qt Quick scene outside the GUI thread.

targetThread specifies the thread on which synchronization and rendering will happen. There is no need to call this function in a single threaded scenario.

Definition at line 215 of file qquickrendercontrol.cpp.

◆ render()

void QQuickRenderControl::render ( )

Renders the scenegraph using the current context.

Definition at line 426 of file qquickrendercontrol.cpp.

◆ renderRequested

void QQuickRenderControl::renderRequested ( )

signal

This signal is emitted when the scene graph needs to be rendered.

It is not necessary to call sync().

Note: Avoid triggering rendering directly when this signal is emitted. Instead, prefer deferring it by using a timer for example. This will lead to better performance.

◆ renderWindow()

virtual QWindow * QQuickRenderControl::renderWindow ( QPoint * offset )

inlinevirtual

Reimplemented in subclasses to return the real window this render control is rendering into.

If offset is non-null, it is set to the offset of the control inside the window.

Note: While not mandatory, reimplementing this function becomes essential for supporting multiple screens with different device pixel ratios and properly positioning popup windows opened from QML. Therefore providing it in subclasses is highly recommended.

Reimplemented in QQuickWidgetRenderControl, and QQuickWidgetRenderControl.

Definition at line 45 of file qquickrendercontrol.h.

◆ renderWindowFor()

QWindow * QQuickRenderControl::renderWindowFor	(	QQuickWindow *	win,
		QPoint *	offset = nullptr )

static

Returns the real window that win is being rendered to, if any.

If offset is non-null, it is set to the offset of the rendering inside its window.

Definition at line 546 of file qquickrendercontrol.cpp.

◆ rhi()

QRhi * QQuickRenderControl::rhi ( ) const

Returns: the QRhi this QQuickRenderControl is associated with.

Note: The QRhi exists only when initialize() has successfully completed. Before that the return value is null.; This function is not applicable and returns null when using the software adaptation of Qt Quick.

Since: 6.6

See also: commandBuffer(), beginFrame(), endFrame()

Definition at line 602 of file qquickrendercontrol.cpp.

◆ samples()

int QQuickRenderControl::samples ( ) const

Returns: the current sample count. 1 or 0 means no multisampling.

Since: 6.0

Definition at line 246 of file qquickrendercontrol.cpp.

◆ sceneChanged

void QQuickRenderControl::sceneChanged ( )

signal

This signal is emitted when the scene graph is updated, meaning that polishItems() and sync() needs to be called.

If sync() returns true, then render() needs to be called.

Note: Avoid triggering polishing, synchronization and rendering directly when this signal is emitted. Instead, prefer deferring it by using a timer for example. This will lead to better performance.

◆ setSamples()

void QQuickRenderControl::setSamples ( int sampleCount )

Sets the number of samples to use for multisampling.

When sampleCount is 0 or 1, multisampling is disabled.

Note: This function is always used in combination with a multisample render target, which means sampleCount must match the sample count passed to QQuickRenderTarget::fromNativeTexture(), which in turn must match the sample count of the native texture.

Since: 6.0

See also: initialize(), QQuickRenderTarget

Definition at line 235 of file qquickrendercontrol.cpp.

◆ sync()

bool QQuickRenderControl::sync ( )

This function is used to synchronize the QML scene with the rendering scene graph.

If a dedicated render thread is used, the GUI thread should be blocked for the duration of this call.

Returns: true if the synchronization changed the scene graph.

Definition at line 357 of file qquickrendercontrol.cpp.

◆ window()

QQuickWindow * QQuickRenderControl::window ( ) const

Returns: the QQuickWindow this QQuickRenderControl is associated with.

Note: A QQuickRenderControl gets associated with a QQuickWindow when constructing the QQuickWindow. The return value from this function is null before that point.

Since: 6.0

Definition at line 583 of file qquickrendercontrol.cpp.

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

qtdeclarative/src/quick/items/qquickrendercontrol.h (ace43e1db17d1bfbf549a5c4c6ef49c3ccaf10fc)
qtdeclarative/src/quick/items/qquickrendercontrol.cpp (b50fee10b97b2d40263bd2c6c45c87d3bc2a2084)

Signals

Public Member Functions

Static Public Member Functions

Protected Member Functions

Additional Inherited Members