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…

Synopsis#

Functions#

def beginFrame ()
def endFrame ()
def initialize ()
def invalidate ()
def polishItems ()
def prepareThread (targetThread)
def render ()
def samples ()
def setSamples (sampleCount)
def sync ()
def window ()

Virtual functions#

def renderWindow (offset)

Signals#

def renderRequested ()
def sceneChanged ()

Static functions#

def renderWindowFor (win[, offset=None])

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

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, 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 grabWindow()

When using a QQuickRenderControl , the QQuickWindow must not be 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 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 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 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:

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.

For key events it may be also necessary to set the focus manually on the desired item. In practice this involves calling 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.

class PySide6.QtQuick.QQuickRenderControl([parent=None])#

Parameters:: parent – PySide6.QtCore.QObject

Constructs a QQuickRenderControl object, with parent object parent.

PySide6.QtQuick.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 like 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