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, 2 insertions, 0 deletions

diff --git a/src/quick/items/qquickrendercontrol.h b/src/quick/items/qquickrendercontrol.h
index e6903653c2..99d1b8ac2d 100644
--- a/src/quick/items/qquickrendercontrol.h
+++ b/src/quick/items/qquickrendercontrol.h
@@ -42,6 +42,7 @@ QT_BEGIN_NAMESPACE
 class QQuickWindow;
 class QOpenGLContext;
 class QQuickRenderControlPrivate;
+class QThread;
 
 class Q_QUICK_EXPORT QQuickRenderControl : public QObject
 {
@@ -51,6 +52,7 @@ public:
     QQuickRenderControl(QObject *parent = 0);
     ~QQuickRenderControl();
 
+    void prepareThread(QThread *targetThread);
     void initialize(QOpenGLContext *gl);
     void invalidate();