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
grab
()def
initialize
(gl)def
invalidate
()def
polishItems
()def
prepareThread
(targetThread)def
render
()def
sync
()
Virtual functions¶
def
renderWindow
(offset)
Signals¶
def
renderRequested
()def
sceneChanged
()
Static functions¶
def
renderWindowFor
(win[, offset=None])
Detailed Description¶
QQuickWindow
andQQuickView
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 usinggrabWindow()
When using a
QQuickRenderControl
, theQQuickWindow
does not have to be shown or even created at all. This means there will not be an underlying native window for it. Instead, theQQuickWindow
instance is associated with the render control, using the overload of theQQuickWindow
constructor, and an OpenGL framebuffer object by callingsetRenderTarget()
.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 forQOpenGLContext
to adopt existing native contexts. Together withQQuickRenderControl
this makes it possible to create aQOpenGLContext
that shares with an external rendering engine’s existing context. This newQOpenGLContext
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 theQQuickWindow
‘s contentItem().Applications will usually have to connect to 4 important signals:
sceneGraphInitialized()
Emitted at some point after callinginitialize()
. Upon this signal, the application is expected to create its framebuffer object and associate it with theQQuickWindow
.
sceneGraphInvalidated()
When the scenegraph resources are released, the framebuffer object can be destroyed too.
renderRequested()
Indicates that the scene has to be rendered by callingrender()
. After making the context current, applications are expected to callrender()
.
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 theQQuickWindow
instance as the receiver.Note
In general
QQuickRenderControl
is supported in combination with all Qt Quick backends. However, some functionality, in particulargrab()
, may not be available in all cases.
- class PySide2.QtQuick.QQuickRenderControl([parent=None])¶
- param parent:
Constructs a
QQuickRenderControl
object, with parent objectparent
.
- PySide2.QtQuick.QQuickRenderControl.grab()¶
- Return type:
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:
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 theQQuickRenderControl
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 theQQuickRenderControl
instance.Once has been called, it is possible to reuse the
QQuickRenderControl
instance by callinginitialize()
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:
targetThread –
PySide2.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:
offset –
PySide2.QtCore.QPoint
- Return type:
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:
offset –
PySide2.QtCore.QPoint
- Return type:
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.
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