Support threading with QQuickRenderControl

Reorganize the rendercontrol example to demonstrate both the single
and multi threaded approaches.

A small helper function is introduced to the QQuickRenderControl API:
The QSGRenderContext has to live on the render thread. Previously there
was no way for applications to move it to the desired thread. This is
now possible.

Pass --threaded to the rendercontrol example to use a separate render thread.

[ChangeLog][QtQuick] QQuickRenderControl can now be used to render the Qt Quick
scene on a dedicated render thread, similarly to how the built-in threaded render
loop operates.

Task-number: QTBUG-42813
Change-Id: I01c3b2ffca8a174d9d2c267a51f2e484ed7b34b3
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

1 files changed, 15 insertions, 1 deletions

diff --git a/src/quick/items/qquickrendercontrol.cpp b/src/quick/items/qquickrendercontrol.cpp
index a666bb59c9..656678a035 100644
--- a/src/quick/items/qquickrendercontrol.cpp
+++ b/src/quick/items/qquickrendercontrol.cpp
@@ -36,7 +36,7 @@
 
 #include <QtCore/QCoreApplication>
 #include <QtCore/QTime>
-#include <QtCore/private/qabstractanimation_p.h>
+#include <QtQuick/private/qquickanimatorcontroller_p.h>
 
 #include <QtGui/QOpenGLContext>
 #include <QtGui/private/qguiapplication_p.h>
@@ -170,6 +170,20 @@ void QQuickRenderControlPrivate::windowDestroyed()
 }
 
 /*!
+  Prepares rendering the Qt Quick scene outside the gui thread.
+
+  \a targetThread specifies the thread on which synchronization and
+  rendering will happen. There is no need to call this function in a
+  single threaded scenario.
+ */
+void QQuickRenderControl::prepareThread(QThread *targetThread)
+{
+    Q_D(QQuickRenderControl);
+    d->rc->moveToThread(targetThread);
+    QQuickWindowPrivate::get(d->window)->animationController->moveToThread(targetThread);
+}
+
+/*!
   Initializes the scene graph resources. The context \a gl has to
   be the current context.