QQuickWindow Class | Qt Quick 5.9

Qt 5.9 | Qt Quick | C++ Classes | QQuickWindow

Qt 5.9.4 Reference Documentation

# QQuickWindow Class

The QQuickWindow class provides the window for displaying a graphical QML scene More...

Header: | #include <QQuickWindow>
qmake: | QT += quick
Since: | Qt 5.0
Instantiated By: | Window
Inherits: | QWindow
Inherited By: | QQuickView

- List of all members, including inherited members
- Obsolete members

## Public Types

enum | CreateTextureOption { TextureHasAlphaChannel, TextureHasMipmaps, TextureOwnsGLTexture, TextureCanUseAtlas, TextureIsOpaque }
flags | CreateTextureOptions
enum | RenderStage { BeforeSynchronizingStage, AfterSynchronizingStage, BeforeRenderingStage, AfterRenderingStage, AfterSwapStage, NoStage }
enum | SceneGraphError { ContextNotAvailable }

## Properties

- activeFocusItem : QQuickItem * const
- color : QColor
- contentItem : QQuickItem * const

- 16 properties inherited from QWindow

## Public Functions

| QQuickWindow(QWindow *parent = Q_NULLPTR)
virtual | ~QQuickWindow()
QQuickItem * | activeFocusItem() const
bool | clearBeforeRendering() const
QColor | color() const
QQuickItem * | contentItem() const
QSGImageNode * | createImageNode() const
QSGNinePatchNode * | createNinePatchNode() const
QSGRectangleNode * | createRectangleNode() const
QSGTexture * | createTextureFromId(uint id, const QSize &size, CreateTextureOptions options = CreateTextureOption()) const
QSGTexture * | createTextureFromImage(const QImage &image, CreateTextureOptions options) const
QSGTexture * | createTextureFromImage(const QImage &image) const
qreal | effectiveDevicePixelRatio() const
QImage | grabWindow()
QQmlIncubationController * | incubationController() const
bool | isPersistentOpenGLContext() const
bool | isPersistentSceneGraph() const
bool | isSceneGraphInitialized() const
QQuickItem * | mouseGrabberItem() const
QOpenGLContext * | openglContext() const
QOpenGLFramebufferObject * | renderTarget() const
uint | renderTargetId() const
QSize | renderTargetSize() const
QSGRendererInterface * | rendererInterface() const
void | resetOpenGLState()
void | scheduleRenderJob(QRunnable *job, RenderStage stage)
void | setClearBeforeRendering(bool enabled)
void | setColor(const QColor &color)
void | setPersistentOpenGLContext(bool persistent)
void | setPersistentSceneGraph(bool persistent)
void | setRenderTarget(QOpenGLFramebufferObject *fbo)
void | setRenderTarget(uint fboId, const QSize &size)

## Reimplemented Public Functions

virtual QAccessibleInterface * | accessibleRoot() const

- 80 public functions inherited from QWindow
- 6 public functions inherited from QSurface

## Public Slots

void | releaseResources()
void | update()

- 22 public slots inherited from QWindow

## Signals

void | activeFocusItemChanged()
void | afterAnimating()
void | afterRendering()
void | afterSynchronizing()
void | beforeRendering()
void | beforeSynchronizing()
void | closing(QQuickCloseEvent *close)
void | colorChanged(const QColor &)
void | frameSwapped()
void | openglContextCreated(QOpenGLContext *context)
void | sceneGraphAboutToStop()
void | sceneGraphError(QQuickWindow::SceneGraphError error, const QString &message)
void | sceneGraphInitialized()
void | sceneGraphInvalidated()

- 18 signals inherited from QWindow

## Static Public Members

bool | hasDefaultAlphaBuffer()
QString | sceneGraphBackend()
void | setDefaultAlphaBuffer(bool useAlpha)
void | setSceneGraphBackend(QSGRendererInterface::GraphicsApi api)
void | setSceneGraphBackend(const QString &backend)

- 1 static public member inherited from QWindow

## Reimplemented Protected Functions

virtual bool | event(QEvent *e)
virtual void | exposeEvent(QExposeEvent *)
virtual void | focusInEvent(QFocusEvent *ev)
virtual void | focusOutEvent(QFocusEvent *ev)
virtual void | hideEvent(QHideEvent *)
virtual void | keyPressEvent(QKeyEvent *e)
virtual void | keyReleaseEvent(QKeyEvent *e)
virtual void | mouseDoubleClickEvent(QMouseEvent *event)
virtual void | mouseMoveEvent(QMouseEvent *event)
virtual void | mousePressEvent(QMouseEvent *event)
virtual void | mouseReleaseEvent(QMouseEvent *event)
virtual void | resizeEvent(QResizeEvent *ev)
virtual void | showEvent(QShowEvent *)
virtual void | wheelEvent(QWheelEvent *event)

- 18 protected functions inherited from QWindow

### Additional Inherited Members

- 18 protected functions inherited from QWindow
- 2 protected variables inherited from QSurface

## Detailed Description

The QQuickWindow class provides the window for displaying a graphical QML scene

QQuickWindow provides the graphical scene management needed to interact with and display a scene of QQuickItems.

A QQuickWindow always has a single invisible root item. To add items to this window, reparent the items to the root item or to an existing item in the scene.

For easily displaying a scene from a QML file, see QQuickView.

### Rendering

QQuickWindow uses a scene graph to represent what needs to be rendered. This scene graph is disconnected from the QML scene and potentially lives in another thread, depending on the platform implementation. Since the rendering scene graph lives independently from the QML scene, it can also be completely released without affecting the state of the QML scene.

The sceneGraphInitialized() signal is emitted on the rendering thread before the QML scene is rendered to the screen for the first time. If the rendering scene graph has been released, the signal will be emitted again before the next frame is rendered.

#### Integration with OpenGL

When using the default OpenGL adaptation, it is possible to integrate OpenGL calls directly into the QQuickWindow using the same OpenGL context as the Qt Quick Scene Graph. This is done by connecting to the QQuickWindow::beforeRendering() or QQuickWindow::afterRendering() signal.

Note: When using QQuickWindow::beforeRendering(), make sure to disable clearing before rendering with QQuickWindow::setClearBeforeRendering().

#### Exposure and Visibility

When a QQuickWindow instance is deliberately hidden with hide() or setVisible(false), it will stop rendering and its scene graph and graphics context might be released. The sceneGraphInvalidated() signal will be emitted when this happens.

Warning: It is crucial that graphics operations and interaction with the scene graph happens exclusively on the rendering thread, primarily during the updatePaintNode() phase.

Warning: As signals related to rendering might be emitted from the rendering thread, connections should be made using Qt::DirectConnection.

#### Resource Management

QML will try to cache images and scene graph nodes to improve performance, but in some low-memory scenarios it might be required to aggressively release these resources. The releaseResources() can be used to force the clean up of certain resources. Calling releaseResources() may result in the entire scene graph and in the case of the OpenGL adaptation the associated context will be deleted. The sceneGraphInvalidated() signal will be emitted when this happens.

Note: All classes with QSG prefix should be used solely on the scene graph's rendering thread. See Scene Graph and Rendering for more information.

#### Context and Surface Formats

While it is possible to specify a QSurfaceFormat for every QQuickWindow by calling the member function setFormat(), windows may also be created from QML by using the Window and ApplicationWindow elements. In this case there is no C++ code involved in the creation of the window instance, yet applications may still wish to set certain surface format values, for example to request a given OpenGL version or profile. Such applications can call the static function QSurfaceFormat::setDefaultFormat() at startup. The specified format will be used for all Quick windows created afterwards.

See also Scene Graph - OpenGL Under QML.

## Member Type Documentation

### enum QQuickWindow::CreateTextureOption
flags QQuickWindow::CreateTextureOptions

The CreateTextureOption enums are used to customize a texture is wrapped.

Constant | Value | Description
--- | --- | ---
`QQuickWindow::TextureHasAlphaChannel` | `0x0001` | The texture has an alpha channel and should be drawn using blending.
`QQuickWindow::TextureHasMipmaps` | `0x0002` | The texture has mipmaps and can be drawn with mipmapping enabled.
`QQuickWindow::TextureOwnsGLTexture` | `0x0004` | The texture object owns the texture id and will delete the OpenGL texture when the texture object is deleted.
`QQuickWindow::TextureCanUseAtlas` | `0x0008` | The image can be uploaded into a texture atlas.
`QQuickWindow::TextureIsOpaque` | `0x0010` | The texture will return false for QSGTexture::hasAlphaChannel() and will not be blended. This flag was added in Qt 5.6.

The CreateTextureOptions type is a typedef for QFlags<CreateTextureOption>. It stores an OR combination of CreateTextureOption values.

### enum QQuickWindow::RenderStage

Constant | Value | Description
--- | --- | ---
`QQuickWindow::BeforeSynchronizingStage` | `0` | Before synchronization.
`QQuickWindow::AfterSynchronizingStage` | `1` | After synchronization.
`QQuickWindow::BeforeRenderingStage` | `2` | Before rendering.
`QQuickWindow::AfterRenderingStage` | `3` | After rendering.
`QQuickWindow::AfterSwapStage` | `4` | After the frame is swapped.
`QQuickWindow::NoStage` | `5` | As soon as possible. This value was added in Qt 5.6.

This enum was introduced or modified in Qt 5.4.

See also Scene Graph and Rendering.

### enum QQuickWindow::SceneGraphError

This enum describes the error in a sceneGraphError() signal.

Constant | Value | Description
--- | --- | ---
`QQuickWindow::ContextNotAvailable` | `1` | graphics context creation failed. This typically means that no suitable OpenGL implementation was found, for example because no graphics drivers are installed and so no OpenGL 2 support is present. On mobile and embedded boards that use OpenGL ES such an error is likely to indicate issues in the windowing system integration and possibly an incorrect configuration of Qt.

This enum was introduced or modified in Qt 5.3.

## Property Documentation

### activeFocusItem : QQuickItem * const

This property holds the item which currently has active focus or `null` if there is no item with active focus.

Access functions:

QQuickItem * | activeFocusItem() const

Notifier signal:

void | activeFocusItemChanged()

### color : QColor

This property holds the color used to clear the OpenGL context.

Setting the clear color has no effect when clearing is disabled. By default, the clear color is white.

Access functions:

QColor | color() const
void | setColor(const QColor &color)

Notifier signal:

void | colorChanged(const QColor &)

See also setClearBeforeRendering() and setDefaultAlphaBuffer().

### contentItem : QQuickItem * const

This property holds the invisible root item of the scene.

A QQuickWindow always has a single invisible root item containing all of its content. To add items to this window, reparent the items to the contentItem or to an existing item in the scene.

Access functions:

QQuickItem * | contentItem() const

## Member Function Documentation

### QQuickWindow::QQuickWindow(QWindow *parent = Q_NULLPTR)

Constructs a window for displaying a QML scene with parent window parent.

### `[virtual]` QQuickWindow::~QQuickWindow()

Destroys the window.

### `[virtual]` QAccessibleInterface *QQuickWindow::accessibleRoot() const

Returns an accessibility interface for this window, or 0 if such an interface cannot be created.

### `[signal]` void QQuickWindow::afterAnimating()

This signal is emitted on the gui thread before requesting the render thread to perform the synchronization of the scene graph.

Unlike the other similar signals, this one is emitted on the gui thread instead of the render thread. It can be used to synchronize external animation systems with the QML content.

This function was introduced in Qt 5.3.

### `[signal]` void QQuickWindow::afterRendering()

This signal is emitted after the scene has completed rendering, before swapbuffers is called.

This signal can be used to paint using raw OpenGL on top of QML content, or to do screen scraping of the current frame buffer.

The OpenGL context used for rendering the scene graph will be bound at this point.

Warning: This signal is emitted from the scene graph rendering thread. If your slot function needs to finish before execution continues, you must make sure that the connection is direct (see Qt::ConnectionType).

Warning: Make very sure that a signal handler for afterRendering() leaves the OpenGL context in the same state as it was when the signal handler was entered. Failing to do so can result in the scene not rendering properly.

See also resetOpenGLState().

### `[signal]` void QQuickWindow::afterSynchronizing()

This signal is emitted after the scene graph is synchronized with the QML state.

This signal can be used to do preparation required after calls to QQuickItem::updatePaintNode(), while the GUI thread is still locked.

The graphics context used for rendering the scene graph will be bound at this point.

Warning: This signal is emitted from the scene graph rendering thread. If your slot function needs to finish before execution continues, you must make sure that the connection is direct (see Qt::ConnectionType).

Warning: When using the OpenGL adaptation, make sure that a signal handler for afterSynchronizing leaves the OpenGL context in the same state as it was when the signal handler was entered. Failing to do so can result in the scene not rendering properly.

This function was introduced in Qt 5.3.

See also resetOpenGLState().

### `[signal]` void QQuickWindow::beforeRendering()

This signal is emitted before the scene starts rendering.

Combined with the modes for clearing the background, this option can be used to paint using raw OpenGL under QML content.

The OpenGL context used for rendering the scene graph will be bound at this point.

Warning: This signal is emitted from the scene graph rendering thread. If your slot function needs to finish before execution continues, you must make sure that the connection is direct (see Qt::ConnectionType).

Warning: Make very sure that a signal handler for beforeRendering leaves the OpenGL context in the same state as it was when the signal handler was entered. Failing to do so can result in the scene not rendering properly.

See also resetOpenGLState().

### `[signal]` void QQuickWindow::beforeSynchronizing()

This signal is emitted before the scene graph is synchronized with the QML state.

This signal can be used to do any preparation required before calls to QQuickItem::updatePaintNode().

The OpenGL context used for rendering the scene graph will be bound at this point.

Warning: This signal is emitted from the scene graph rendering thread. If your slot function needs to finish before execution continues, you must make sure that the connection is direct (see Qt::ConnectionType).

Warning: Make very sure that a signal handler for beforeSynchronizing leaves the GL context in the same state as it was when the signal handler was entered. Failing to do so can result in the scene not rendering properly.

See also resetOpenGLState().

### bool QQuickWindow::clearBeforeRendering() const

Returns whether clearing of the color buffer is done before rendering or not.

See also setClearBeforeRendering().

### `[signal]` void QQuickWindow::closing(QQuickCloseEvent *close)

This signal is emitted when the window receives the event close from the windowing system.

This function was introduced in Qt 5.1.

### QSGImageNode *QQuickWindow::createImageNode() const

Creates a simple image node. When the scenegraph is not initialized, the return value is null.

This is cross-backend alternative to constructing a QSGSimpleTextureNode directly.

This function was introduced in Qt 5.8.

See also QSGImageNode.

### QSGNinePatchNode *QQuickWindow::createNinePatchNode() const

Creates a nine patch node. When the scenegraph is not initialized, the return value is null.

This function was introduced in Qt 5.8.

### QSGRectangleNode *QQuickWindow::createRectangleNode() const

Creates a simple rectangle node. When the scenegraph is not initialized, the return value is null.

This is cross-backend alternative to constructing a QSGSimpleRectNode directly.

This function was introduced in Qt 5.8.

See also QSGRectangleNode.

### QSGTexture *QQuickWindow::createTextureFromId(uint id, const QSize &size, CreateTextureOptions options = CreateTextureOption()) const

Creates a new QSGTexture object from an existing OpenGL texture id and size.

The caller of the function is responsible for deleting the returned texture.

The returned texture will be using `GL_TEXTURE_2D` as texture target and assumes that internal format is `GL_RGBA`. Reimplement QSGTexture to create textures with different parameters.

Use options to customize the texture attributes. The TextureUsesAtlas option is ignored.

Warning: This function will return null if the scenegraph has not yet been initialized or OpenGL is not in use.

Note: This function only has an effect when using the default OpenGL scene graph adaptation.

See also sceneGraphInitialized() and QSGTexture.

### QSGTexture *QQuickWindow::createTextureFromImage(const QImage &image, CreateTextureOptions options) const

Creates a new QSGTexture from the supplied image. If the image has an alpha channel, the corresponding texture will have an alpha channel.

The caller of the function is responsible for deleting the returned texture. For example whe using the OpenGL adaptation the actual OpenGL texture will be deleted when the texture object is deleted.

When options contains TextureCanUseAtlas, the engine may put the image into a texture atlas. Textures in an atlas need to rely on QSGTexture::normalizedTextureSubRect() for their geometry and will not support QSGTexture::Repeat. Other values from CreateTextureOption are ignored.

When options contains TextureIsOpaque, the engine will create an RGB texture which returns false for QSGTexture::hasAlphaChannel(). Opaque textures will in most cases be faster to render. When this flag is not set, the texture will have an alpha channel based on the image's format.

When options contains TextureHasMipmaps, the engine will create a texture which can use mipmap filtering. Mipmapped textures can not be in an atlas.

When using the OpenGL adaptation, the returned texture will be using `GL_TEXTURE_2D` as texture target and `GL_RGBA` as internal format. Reimplement QSGTexture to create textures with different parameters.

Warning: This function will return 0 if the scene graph has not yet been initialized.

Warning: The returned texture is not memory managed by the scene graph and must be explicitly deleted by the caller on the rendering thread. This is achieved by deleting the texture from a QSGNode destructor or by using deleteLater() in the case where the texture already has affinity to the rendering thread.

This function can be called from any thread.

See also sceneGraphInitialized() and QSGTexture.

### QSGTexture *QQuickWindow::createTextureFromImage(const QImage &image) const

This is an overloaded function.

### qreal QQuickWindow::effectiveDevicePixelRatio() const

Returns the device pixel ratio for this window.

This is different from QWindow::devicePixelRatio() in that it supports redirected rendering via QQuickRenderControl. When using a QQuickRenderControl, the QQuickWindow is often not created, meaning it is never shown and there is no underlying native window created in the windowing system. As a result, querying properties like the device pixel ratio cannot give correct results. Use this function instead.

See also QWindow::devicePixelRatio().

### `[virtual protected]` bool QQuickWindow::event(QEvent *e)

Reimplemented from QWindow::event().

### `[virtual protected]` void QQuickWindow::exposeEvent(QExposeEvent *)

Reimplemented from QWindow::exposeEvent().

### `[virtual protected]` void QQuickWindow::focusInEvent(QFocusEvent *ev)

Reimplemented from QWindow::focusInEvent().

### `[virtual protected]` void QQuickWindow::focusOutEvent(QFocusEvent *ev)

Reimplemented from QWindow::focusOutEvent().

### `[signal]` void QQuickWindow::frameSwapped()

This signal is emitted when a frame has been queued for presenting. With vertical synchronization enabled the signal is emitted at most once per vsync interval in a continuously animating scene.

This signal will be emitted from the scene graph rendering thread.

### QImage QQuickWindow::grabWindow()

Grabs the contents of the window and returns it as an image.

It is possible to call the grabWindow() function when the window is not visible. This requires that the window is created and has a valid size and that no other QQuickWindow instances are rendering in the same process.

Warning: Calling this function will cause performance problems.

Warning: This function can only be called from the GUI thread.

### `[static]` bool QQuickWindow::hasDefaultAlphaBuffer()

Returns whether to use alpha transparency on newly created windows.

This function was introduced in Qt 5.1.

See also setDefaultAlphaBuffer().

### `[virtual protected]` void QQuickWindow::hideEvent(QHideEvent *)

Reimplemented from QWindow::hideEvent().

### QQmlIncubationController *QQuickWindow::incubationController() const

Returns an incubation controller that splices incubation between frames for this window. QQuickView automatically installs this controller for you, otherwise you will need to install it yourself using QQmlEngine::setIncubationController().

The controller is owned by the window and will be destroyed when the window is deleted.

### bool QQuickWindow::isPersistentOpenGLContext() const

Returns whether the OpenGL context can be released during the lifetime of the QQuickWindow.

Note: This is a hint. When and how this happens is implementation specific. It also only has an effect when using the default OpenGL scene graph adaptation

### bool QQuickWindow::isPersistentSceneGraph() const

Returns whether the scene graph nodes and resources can be released during the lifetime of this QQuickWindow.

Note: This is a hint. When and how this happens is implementation specific.

### bool QQuickWindow::isSceneGraphInitialized() const

Returns true if the scene graph has been initialized; otherwise returns false.

### `[virtual protected]` void QQuickWindow::keyPressEvent(QKeyEvent *e)

Reimplemented from QWindow::keyPressEvent().

### `[virtual protected]` void QQuickWindow::keyReleaseEvent(QKeyEvent *e)

Reimplemented from QWindow::keyReleaseEvent().

### `[virtual protected]` void QQuickWindow::mouseDoubleClickEvent(QMouseEvent *event)

Reimplemented from QWindow::mouseDoubleClickEvent().

### QQuickItem *QQuickWindow::mouseGrabberItem() const

Returns the item which currently has the mouse grab.

### `[virtual protected]` void QQuickWindow::mouseMoveEvent(QMouseEvent *event)

Reimplemented from QWindow::mouseMoveEvent().

### `[virtual protected]` void QQuickWindow::mousePressEvent(QMouseEvent *event)

Reimplemented from QWindow::mousePressEvent().

### `[virtual protected]` void QQuickWindow::mouseReleaseEvent(QMouseEvent *event)

Reimplemented from QWindow::mouseReleaseEvent().

### QOpenGLContext *QQuickWindow::openglContext() const

Returns the OpenGL context used for rendering.

If the scene graph is not ready, or the scene graph is not using OpenGL, this function will return null.

Note: If using a scene graph adaptation other than OpenGL this function will return nullptr.

See also sceneGraphInitialized() and sceneGraphInvalidated().

### `[signal]` void QQuickWindow::openglContextCreated(QOpenGLContext *context)

This signal is emitted on the gui thread when the OpenGL context for this window is created, before it is made current.

Some implementations will share the same OpenGL context between multiple QQuickWindow instances. The openglContextCreated() signal will in this case only be emitted for the first window, when the OpenGL context is actually created.

QQuickWindow::openglContext() will still return 0 for this window until after the QQuickWindow::sceneGraphInitialize() has been emitted.

Note: This signal will only be emmited when using the default OpenGL scene graph adaptation.

This function was introduced in Qt 5.3.

### `[slot]` void QQuickWindow::releaseResources()

This function tries to release redundant resources currently held by the QML scene.

Calling this function might result in the scene graph and the OpenGL context used for rendering being released to release graphics memory. If this happens, the sceneGraphInvalidated() signal will be called, allowing users to clean up their own graphics resources. The setPersistentOpenGLContext() and setPersistentSceneGraph() functions can be used to prevent this from happening, if handling the cleanup is not feasible in the application, at the cost of higher memory usage.

See also sceneGraphInvalidated(), setPersistentOpenGLContext(), and setPersistentSceneGraph().

### QOpenGLFramebufferObject *QQuickWindow::renderTarget() const

Returns the render target for this window.

The default is to render to the surface of the window, in which case the render target is 0.

Note: This function will return nullptr when not using the OpenGL scene graph adaptation.

See also setRenderTarget().

### uint QQuickWindow::renderTargetId() const

Returns the FBO id of the render target when set; otherwise returns 0.

### QSize QQuickWindow::renderTargetSize() const

Returns the size of the currently set render target; otherwise returns an empty size.

### QSGRendererInterface *QQuickWindow::rendererInterface() const

Returns the current renderer interface. The value is always valid and is never null.

Note: This function can be called at any time after constructing the QQuickWindow, even while isSceneGraphInitialized() is still false. However, some renderer interface functions, in particular QSGRendererInterface::getResource() will not be functional until the scenegraph is up and running. Backend queries, like QSGRendererInterface::graphicsApi() or QSGRendererInterface::shaderType(), will always be functional on the other hand.

Note: The ownership of the returned pointer stays with Qt. The returned instance may or may not be shared between different QQuickWindow instances, depending on the scenegraph backend in use. Therefore applications are expected to query the interface object for each QQuickWindow instead of reusing the already queried pointer.

This function was introduced in Qt 5.8.

See also QSGRenderNode and QSGRendererInterface.

### void QQuickWindow::resetOpenGLState()

Call this function to reset the OpenGL context its default state.

The scene graph uses the OpenGL context and will both rely on and clobber its state. When mixing raw OpenGL commands with scene graph rendering, this function provides a convenient way of resetting the OpenGL context state back to its default values.

This function does not touch state in the fixed-function pipeline.

This function does not clear the color, depth and stencil buffers. Use QQuickWindow::setClearBeforeRendering to control clearing of the color buffer. The depth and stencil buffer might be clobbered by the scene graph renderer. Clear these manually on demand.

Note: This function only has an effect when using the default OpenGL scene graph adaptation.

This function was introduced in Qt 5.2.

See also QQuickWindow::beforeRendering().

### `[virtual protected]` void QQuickWindow::resizeEvent(QResizeEvent *ev)

Reimplemented from QWindow::resizeEvent().

### `[signal]` void QQuickWindow::sceneGraphAboutToStop()

This signal is emitted on the render thread when the scene graph is about to stop rendering. This happens usually because the window has been hidden.

Applications may use this signal to release resources, but should be prepared to reinstantiated them again fast. The scene graph and the graphics context are not released at this time.

Warning: This signal is emitted from the scene graph rendering thread. If your slot function needs to finish before execution continues, you must make sure that the connection is direct (see Qt::ConnectionType).

Warning: Make very sure that a signal handler for sceneGraphAboutToStop() leaves the graphics context in the same state as it was when the signal handler was entered. Failing to do so can result in the scene not rendering properly.

This function was introduced in Qt 5.3.

See also sceneGraphInvalidated() and resetOpenGLState().

### `[static]` QString QQuickWindow::sceneGraphBackend()

Returns the requested Qt Quick scenegraph backend.

Note: The return value of this function may still be outdated by subsequent calls to setSceneGraphBackend() until the first QQuickWindow in the application has been constructed.

This function was introduced in Qt 5.9.

See also setSceneGraphBackend().

### `[signal]` void QQuickWindow::sceneGraphError(QQuickWindow::SceneGraphError error, const QString &message)

This signal is emitted when an error occurred during scene graph initialization.

Applications should connect to this signal if they wish to handle errors, like graphics context creation failures, in a custom way. When no slot is connected to the signal, the behavior will be different: Quick will print the message, or show a message box, and terminate the application.

This signal will be emitted from the gui thread.

This function was introduced in Qt 5.3.

### `[signal]` void QQuickWindow::sceneGraphInitialized()

This signal is emitted when the scene graph has been initialized.

This signal will be emitted from the scene graph rendering thread.

### `[signal]` void QQuickWindow::sceneGraphInvalidated()

This signal is emitted when the scene graph has been invalidated.

This signal implies that the graphics rendering context used has been invalidated and all user resources tied to that context should be released.

In the case of the default OpenGL adaptation the context of this window will be bound when this function is called. The only exception is if the native OpenGL has been destroyed outside Qt's control, for instance through EGL_CONTEXT_LOST.

This signal will be emitted from the scene graph rendering thread.

### void QQuickWindow::scheduleRenderJob(QRunnable *job, RenderStage stage)

Schedules job to run when the rendering of this window reaches the given stage.

This is a convenience to the equivalent signals in QQuickWindow for "one shot" tasks.

The window takes ownership over job and will delete it when the job is completed.

If rendering is shut down before job has a chance to run, the job will be run and then deleted as part of the scene graph cleanup. If the window is never shown and no rendering happens before the QQuickWindow is destroyed, all pending jobs will be destroyed without their run() method being called.

If the rendering is happening on a different thread, then the job will happen on the rendering thread.

If stage is NoStage, job will be run at the earliest opportunity whenever the render thread is not busy rendering a frame. If there is no OpenGL context available or the window is not exposed at the time the job is either posted or handled, it is deleted without executing the run() method. If a non-threaded renderer is in use, the run() method of the job is executed synchronously. The OpenGL context is changed to the renderer context before executing a NoStage job.

Note: This function does not trigger rendering; the jobs targeting any other stage than NoStage will be stored run until rendering is triggered elsewhere. To force the job to run earlier, call QQuickWindow::update();

This function was introduced in Qt 5.4.

See also beforeRendering(), afterRendering(), beforeSynchronizing(), afterSynchronizing(), frameSwapped(), and sceneGraphInvalidated().

### void QQuickWindow::setClearBeforeRendering(bool enabled)

Sets whether the scene graph rendering of QML should clear the color buffer before it starts rendering to enabled.

By disabling clearing of the color buffer, it is possible to render OpengGL content under the scene graph.

The color buffer is cleared by default.

See also clearBeforeRendering() and beforeRendering().

### `[static]` void QQuickWindow::setDefaultAlphaBuffer(bool useAlpha)

useAlpha specifies whether to use alpha transparency on newly created windows.

In any application which expects to create translucent windows, it's necessary to set this to true before creating the first QQuickWindow. The default value is false.

This function was introduced in Qt 5.1.

See also hasDefaultAlphaBuffer().

### void QQuickWindow::setPersistentOpenGLContext(bool persistent)

Sets whether the OpenGL context should be preserved, and cannot be released until the last window is deleted, to persistent. The default value is true.

The OpenGL context can be released to free up graphics resources when the window is obscured, hidden or not rendering. When this happens is implementation specific.

The QOpenGLContext::aboutToBeDestroyed() signal is emitted from the QQuickWindow::openglContext() when the OpenGL context is about to be released. The QQuickWindow::sceneGraphInitialized() signal is emitted when a new OpenGL context is created for this window. Make a Qt::DirectConnection to these signals to be notified.

The OpenGL context is still released when the last QQuickWindow is deleted.

Note: This only has an effect when using the default OpenGL scene graph adaptation.

See also isPersistentOpenGLContext(), setPersistentSceneGraph(), QOpenGLContext::aboutToBeDestroyed(), and sceneGraphInitialized().

### void QQuickWindow::setPersistentSceneGraph(bool persistent)

Sets whether the scene graph nodes and resources can be released to persistent. The default value is true.

The scene graph nodes and resources can be released to free up graphics resources when the window is obscured, hidden or not rendering. When this happens is implementation specific.

The QQuickWindow::sceneGraphInvalidated() signal is emitted when cleanup occurs. The QQuickWindow::sceneGraphInitialized() signal is emitted when a new scene graph is recreated for this window. Make a Qt::DirectConnection to these signals to be notified.

The scene graph nodes and resources are still released when the last QQuickWindow is deleted.

See also isPersistentSceneGraph(), setPersistentOpenGLContext(), sceneGraphInvalidated(), and sceneGraphInitialized().

### void QQuickWindow::setRenderTarget(QOpenGLFramebufferObject *fbo)

Sets the render target for this window to be fbo.

The specified fbo must be created in the context of the window or one that shares with it.

Note: This function only has an effect when using the default OpenGL scene graph adaptation.

Warning: This function can only be called from the thread doing the rendering.

See also renderTarget().

### void QQuickWindow::setRenderTarget(uint fboId, const QSize &size)

This is an overloaded function.

Sets the render target for this window to be an FBO with fboId and size.

The specified FBO must be created in the context of the window or one that shares with it.

Note: This function only has an effect when using the default OpenGL scene graph adaptation.

Warning: This function can only be called from the thread doing the rendering.

### `[static]` void QQuickWindow::setSceneGraphBackend(QSGRendererInterface::GraphicsApi api)

Requests a Qt Quick scenegraph backend for the specified graphics api. Backends can either be built-in or be installed in form of dynamically loaded plugins.

Note: The call to the function must happen before constructing the first QQuickWindow in the application. It cannot be changed afterwards.

If the selected backend is invalid or an error occurs, the default backend (OpenGL or software, depending on the Qt configuration) is used.

This function was introduced in Qt 5.8.

See also sceneGraphBackend().

### `[static]` void QQuickWindow::setSceneGraphBackend(const QString &backend)

Requests the specified Qt Quick scenegraph backend. Backends can either be built-in or be installed in form of dynamically loaded plugins.

This is an overloaded function.

Note: The call to the function must happen before constructing the first QQuickWindow in the application. It cannot be changed afterwards.

If backend is invalid or an error occurs, the default backend (OpenGL or software, depending on the Qt configuration) is used.

Note: Calling this function is equivalent to setting the `QT_QUICK_BACKEND` or `QMLSCENE_DEVICE` environment variables. However, this API is safer to use in applications that spawn other processes as there is no need to worry about environment inheritance.

This function was introduced in Qt 5.8.

### `[virtual protected]` void QQuickWindow::showEvent(QShowEvent *)

Reimplemented from QWindow::showEvent().

### `[slot]` void QQuickWindow::update()

Schedules the window to render another frame.

Calling QQuickWindow::update() differs from QQuickItem::update() in that it always triggers a repaint, regardless of changes in the underlying scene graph or not.

### `[virtual protected]` void QQuickWindow::wheelEvent(QWheelEvent *event)

Reimplemented from QWindow::wheelEvent().