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, 4 deletions

diff --git a/examples/quick/rendercontrol/main.cpp b/examples/quick/rendercontrol/main.cpp
index d362278ddf..e61eb110aa 100644
--- a/examples/quick/rendercontrol/main.cpp
+++ b/examples/quick/rendercontrol/main.cpp
@@ -39,13 +39,24 @@
 ****************************************************************************/
 
 #include <QGuiApplication>
-#include "window.h"
+#include "window_singlethreaded.h"
+#include "window_multithreaded.h"
 
 int main(int argc, char **argv)
 {
     QGuiApplication app(argc, argv);
-    Window window;
-    window.resize(1024, 768);
-    window.show();
+
+    QScopedPointer<QWindow> window;
+    if (QCoreApplication::arguments().contains(QLatin1String("--threaded"))) {
+        qWarning("Using separate Qt Quick render thread");
+        window.reset(new WindowMultiThreaded);
+    } else {
+        qWarning("Using single-threaded rendering");
+        window.reset(new WindowSingleThreaded);
+    }
+
+    window->resize(1024, 768);
+    window->show();
+
     return app.exec();
 }