QQuickWindow Class

Member Function Documentation

QQuickWindow::QQuickWindow(QWindow *parent = nullptr)

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

[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. At the same time this means that this signal is not suitable for triggering graphics operations.

This function was introduced in Qt 5.3.

[signal] void QQuickWindow::afterRenderPassRecording()

This signal is emitted after the scenegraph has recorded the commands for its main render pass, but the pass is not yet finalized on the command buffer.

This signal is applicable when using the RHI graphics abstraction with the scenegraph. It is emitted earlier than afterRendering() and it guarantees that not just the frame, but also the recording of the scenegraph's main render pass is still active. This allows inserting commands without having to generate an entire, separate render pass (which would typically clear the attached images). The native graphics objects can be queried via QSGRendererInterface.

When not running with the RHI (and using OpenGL directly), the signal is emitted after the renderer has finished its rendering, but before afterRendering(). This makes it possible to create applications that function identically both with and without the RHI.

This function was introduced in Qt 5.14.

[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.

When using the RHI, the signal is emitted after scene graph has added its commands to the command buffer, which is not yet submitted to the graphics queue. If desired, the slot function connected to this signal can query native resources, like the command buffer, before via QSGRendererInterface. Note however that the render pass (or passes) are already recorded at this point and it is not possible to add more commands within the scenegraph's pass. Instead, use afterRenderPassRecording() for that. This signal has therefore limited use and is rarely needed in an RHI-based setup. Rather, it is the combination of beforeRendering() + beforeRenderPassRecording() or beforeRendering() + afterRenderPassRecording() that is typically used to achieve under- or overlaying of the custom rendering.

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.

This function was introduced in Qt 5.3.

See also resetOpenGLState().

[signal] void QQuickWindow::beforeRenderPassRecording()

This signal is emitted before the scenegraph starts recording commands for the main render pass. (Layers have their own passes and are fully recorded by the time this signal is emitted.) The render pass is already active on the command buffer when the signal is emitted.

This signal is applicable when using the RHI graphics abstraction with the scenegraph. It is emitted later than beforeRendering() and it guarantees that not just the frame, but also the recording of the scenegraph's main render pass is active. This allows inserting commands without having to generate an entire, separate render pass (which would typically clear the attached images). The native graphics objects can be queried via QSGRendererInterface.

When not running with the RHI (and using OpenGL directly), the signal is emitted after the renderer has cleared the render target. This makes it possible to create applications that function identically both with and without the RHI.

This function was introduced in Qt 5.14.

[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.

When using the RHI, the signal is emitted after the preparations for the frame have been done, meaning there is a command buffer in recording mode, where applicable. If desired, the slot function connected to this signal can query native resources like the command before via QSGRendererInterface. Note however that the recording of the main render pass is not yet started at this point and it is not possible to add commands within that pass. Starting a pass means clearing the color, depth, and stencil buffers so it is not possible to achieve an underlay type of rendering by just connecting to this signal. Rather, connect to beforeRenderPassRecording(). However, connecting to this signal is still important if the recording of copy type of commands is desired since those cannot be enqueued within a render pass.

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.

See also resetOpenGLState().

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

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

On macOs, Qt will create a menu item Quit if there is no menu item whose text is "quit" or "exit". This menu item calls the QCoreApplication::quit signal, not the QQuickWindow::closing() signal.

This function was introduced in Qt 5.1.

See also QMenuBar as a Global Menu Bar.

[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.

[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::sceneGraphInitialized() has been emitted.

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().

[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.

This function was introduced in Qt 5.3.

See also sceneGraphInvalidated() and resetOpenGLState().

[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.

[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.

[override virtual] QQuickWindow::~QQuickWindow()

Destroys the window.

[override virtual] QAccessibleInterface *QQuickWindow::accessibleRoot() const

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

void QQuickWindow::beginExternalCommands()

When mixing raw graphics (OpenGL, Vulkan, Metal, etc.) commands with scene graph rendering, it is necessary to call this function before recording commands to the command buffer used by the scene graph to render its main render pass. This is to avoid clobbering state.

In practice this function is often called from a slot connected to the beforeRenderPassRecording() or afterRenderPassRecording() signals.

The function does not need to be called when recording commands to the application's own command buffer (such as, a VkCommandBuffer or MTLCommandBuffer + MTLRenderCommandEncoder created and managed by the application, not retrieved from the scene graph). With graphics APIs where no native command buffer concept is exposed (OpenGL, Direct 3D 11), beginExternalCommands() and endExternalCommands() together provide a replacement for resetOpenGLState().

Calling this function and endExternalCommands() is not necessary within the render() implementation of a QSGRenderNode because the scene graph performs the necessary steps implicitly for render nodes.

Native graphics objects (such as, graphics device, command buffer or encoder) are accessible via QSGRendererInterface::getResource().

This function was introduced in Qt 5.14.

See also endExternalCommands() and resetOpenGLState().

bool QQuickWindow::clearBeforeRendering() const

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

See also setClearBeforeRendering().

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::createTextureFromImage(const QImage &image, QQuickWindow::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.

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.

QSGTexture *QQuickWindow::createTextureFromNativeObject(QQuickWindow::NativeObjectType type, const void *nativeObjectPtr, int nativeLayout, const QSize &size, QQuickWindow::CreateTextureOptions options = CreateTextureOption()) const

Creates a new QSGTexture object from an existing native object.

The native object is wrapped, but not owned, by the resulting QSGTexture. The caller of the function is responsible for deleting the returned QSGTexture, but that will not destroy the underlying native object.

type specifies the type of the object. In practice the type is NativeObjectTexture, indicating that the native object is a texture or image of the underlying graphics API. Other types may be introduced in the future.

This function is currently suitable for 2D RGBA textures only.

Unlike createTextureFromId(), this function supports both direct OpenGL usage and the RHI abstracted rendering path.

Use options to customize the texture attributes. Only the TextureHasAlphaChannel and TextureHasMipmaps are taken into account here.

size specifies the size in pixels.

nativeObjectPtr is a pointer to the native object handle. With OpenGL, the native handle is a GLuint value, so nativeObjectPtr is then a pointer to a GLuint. With Vulkan, the native handle is a VkImage, so nativeObjectPtr is a pointer to a VkImage. With Direct3D 11 and Metal nativeObjectPtr is a pointer to a ID3D11Texture2D or MTLTexture pointer.

nativeLayout is only used for APIs like Vulkan. When applicable, it must specify the current image layout, such as, a VkImageLayout value.

This function was introduced in Qt 5.14.

See also sceneGraphInitialized(), QSGTexture, and QSGTexture::nativeTexture().

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().

void QQuickWindow::endExternalCommands()

When mixing raw graphics (OpenGL, Vulkan, Metal, etc.) commands with scene graph rendering, it is necessary to call this function after recording commands to the command buffer used by the scene graph to render its main render pass. This is to avoid clobbering state.

In practice this function is often called from a slot connected to the beforeRenderPassRecording() or afterRenderPassRecording() signals.

The function does not need to be called when recording commands to the application's own command buffer (such as, a VkCommandBuffer or MTLCommandBuffer + MTLRenderCommandEncoder created and managed by the application, not retrieved from the scene graph). With graphics APIs where no native command buffer concept is exposed (OpenGL, Direct 3D 11), beginExternalCommands() and endExternalCommands() together provide a replacement for resetOpenGLState().

Calling this function and beginExternalCommands() is not necessary within the render() implementation of a QSGRenderNode because the scene graph performs the necessary steps implicitly for render nodes.

This function was introduced in Qt 5.14.

See also beginExternalCommands().

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

Reimplements: QWindow::event(QEvent *ev).

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

Reimplements: QWindow::exposeEvent(QExposeEvent *ev).

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

Reimplements: QWindow::focusInEvent(QFocusEvent *ev).

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

Reimplements: QWindow::focusOutEvent(QFocusEvent *ev).

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.

const QQuickWindow::GraphicsStateInfo &QQuickWindow::graphicsStateInfo()

Returns a reference to a GraphicsStateInfo struct describing some of the RHI's internal state, in particular, the double or tripple buffering status of the backend (such as, the Vulkan or Metal integrations). This is relevant when the underlying graphics APIs is Vulkan or Metal, and the external rendering code wishes to perform double or tripple buffering of its own often-changing resources, such as, uniform buffers, in order to avoid stalling the pipeline.

[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().

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

Reimplements: QWindow::hideEvent(QHideEvent *ev).

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.

bool QQuickWindow::isPersistentSceneGraph() const

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

bool QQuickWindow::isSceneGraphInitialized() const

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

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

Reimplements: QWindow::keyPressEvent(QKeyEvent *ev).

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

Reimplements: QWindow::keyReleaseEvent(QKeyEvent *ev).

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

Reimplements: QWindow::mouseDoubleClickEvent(QMouseEvent *ev).

QQuickItem *QQuickWindow::mouseGrabberItem() const

Returns the item which currently has the mouse grab.

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

Reimplements: QWindow::mouseMoveEvent(QMouseEvent *ev).

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

Reimplements: QWindow::mousePressEvent(QMouseEvent *ev).

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

Reimplements: QWindow::mouseReleaseEvent(QMouseEvent *ev).

QOpenGLContext *QQuickWindow::openglContext() const

Returns the OpenGL context used for rendering.

See also sceneGraphInitialized() and sceneGraphInvalidated().

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.

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.

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.

This function was introduced in Qt 5.2.

See also QQuickWindow::beforeRendering(), beginExternalCommands(), and endExternalCommands().

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

Reimplements: QWindow::resizeEvent(QResizeEvent *ev).

[static] QString QQuickWindow::sceneGraphBackend()

Returns the requested Qt Quick scenegraph backend.

This function was introduced in Qt 5.9.

See also setSceneGraphBackend().

void QQuickWindow::scheduleRenderJob(QRunnable *job, QQuickWindow::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.

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(), beforeRendering(), and beforeRenderPassRecording().

[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.

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

void QQuickWindow::setPersistentSceneGraph(bool persistent)

Sets whether the scene graph nodes and resources are persistent. Persistent means the nodes and resources cannot be released. 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.

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.

[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.

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.

If 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.

[static] void QQuickWindow::setTextRenderType(QQuickWindow::TextRenderType renderType)

Sets the default render type of text-like elements in Qt Quick to renderType.

This function was introduced in Qt 5.10.

See also textRenderType().

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

Reimplements: QWindow::showEvent(QShowEvent *ev).

[override virtual protected] void QQuickWindow::tabletEvent(QTabletEvent *event)

Reimplements: QWindow::tabletEvent(QTabletEvent *ev).

[static] QQuickWindow::TextRenderType QQuickWindow::textRenderType()

Returns the render type of text-like elements in Qt Quick. The default is QQuickWindow::QtTextRendering.

This function was introduced in Qt 5.10.

See also setTextRenderType().

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

Reimplements: QWindow::wheelEvent(QWheelEvent *ev).