QQuickRenderControl

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

Inheritance diagram of PySide2.QtQuick.QQuickRenderControl

Synopsis

Functions

Virtual functions

Signals

Static functions

Detailed Description

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 renderers, it might be beneficial to get the scene into a texture that can then be used in arbitrary ways by the external rendering engine. QQuickRenderControl makes this possible in a hardware accelerated manner, unlike the performance-wise limited alternative of using grabWindow()

When using a QQuickRenderControl , the QQuickWindow does not have to be shown or even created at all. This means there will not be an underlying native window for it. Instead, the QQuickWindow instance is associated with the render control, using the overload of the QQuickWindow constructor, and an OpenGL framebuffer object by calling setRenderTarget() .

Management of the context and framebuffer object is up to the application. The context that will be used by Qt Quick must be created before calling initialize() . The creation of the framebuffer 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.

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:

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

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

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

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

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

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.

class PySide2.QtQuick.QQuickRenderControl([parent=None])
param parent

PySide2.QtCore.QObject

Constructs a QQuickRenderControl object, with parent object parent .

PySide2.QtQuick.QQuickRenderControl.grab()
Return type

PySide2.QtGui.QImage

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

Note

Requires the context to be current.

PySide2.QtQuick.QQuickRenderControl.initialize(gl)
Parameters

glPySide2.QtGui.QOpenGLContext

Initializes the scene graph resources. The context gl has to be the current OpenGL context or null if it is not relevant because a Qt Quick backend other than OpenGL is in use.

Note

Qt Quick does not take ownership of the context. It is up to the application to destroy it after a call to invalidate() or after the QQuickRenderControl instance is destroyed.

PySide2.QtQuick.QQuickRenderControl.invalidate()

Stop rendering and release resources. Requires a current context.

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. Pay attention however to the fact that this requires the context, that was passed to initialize() , to be the current one at the time of destroying the QQuickRenderControl instance.

Once 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::persistentOpenGLContext() into account. This means that context-specific resources are always released.

PySide2.QtQuick.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.

PySide2.QtQuick.QQuickRenderControl.prepareThread(targetThread)
Parameters

targetThreadPySide2.QtCore.QThread

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.

PySide2.QtQuick.QQuickRenderControl.render()

Renders the scenegraph using the current context.

PySide2.QtQuick.QQuickRenderControl.renderRequested()
PySide2.QtQuick.QQuickRenderControl.renderWindow(offset)
Parameters

offsetPySide2.QtCore.QPoint

Return type

PySide2.QtGui.QWindow

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

If offset in 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.

static PySide2.QtQuick.QQuickRenderControl.renderWindowFor(win[, offset=None])
Parameters
Return type

PySide2.QtGui.QWindow

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

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

PySide2.QtQuick.QQuickRenderControl.sceneChanged()
PySide2.QtQuick.QQuickRenderControl.sync()
Return type

bool

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.