QAspectEngine owns the root of the scene

The scene root is now also enforced to be a QEntity as that is what we
were checking for in the backend anyway as it is impossible to create
a plain QNode.

This is another step towards solving the shutdown crashing bug.

Change-Id: I8508afa80ec9e99954ab867be1ed28bc35405e79
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>

14 files changed, 66 insertions, 53 deletions

diff --git a/examples/bigscene-cpp/main.cpp b/examples/bigscene-cpp/main.cpp
index b7b6561bc..6d252c459 100644
--- a/examples/bigscene-cpp/main.cpp
+++ b/examples/bigscene-cpp/main.cpp
@@ -136,7 +136,7 @@ int main(int ac, char **av)
         e->setParent(root);
     }
 
-    view.setRootObject(root);
+    view.setRootEntity(root);
     view.show();
     return app.exec();
 }
diff --git a/examples/cpp_example/main.cpp b/examples/cpp_example/main.cpp
index d6d590955..22c1218b9 100644
--- a/examples/cpp_example/main.cpp
+++ b/examples/cpp_example/main.cpp
@@ -148,8 +148,7 @@ int main(int ac, char **av)
     rootEntity->addComponent(frameGraph);
 
     // Set root object of the scene
-    view.setRootObject(rootEntity);
-    // Show window
+    view.setRootEntity(rootEntity);
     view.show();
 
     return app.exec();
diff --git a/examples/cylinder-cpp/main.cpp b/examples/cylinder-cpp/main.cpp
index c11435346..20800f389 100644
--- a/examples/cylinder-cpp/main.cpp
+++ b/examples/cylinder-cpp/main.cpp
@@ -132,8 +132,7 @@ int main(int argc, char **argv)
     rootEntity->addComponent(frameGraph);
 
     // Set root object of the scene
-    view.setRootObject(rootEntity);
-    // Show window
+    view.setRootEntity(rootEntity);
     view.show();
 
     return app.exec();
diff --git a/examples/deferred-renderer-cpp/main.cpp b/examples/deferred-renderer-cpp/main.cpp
index d91029a2f..0d0c065b9 100644
--- a/examples/deferred-renderer-cpp/main.cpp
+++ b/examples/deferred-renderer-cpp/main.cpp
@@ -185,8 +185,7 @@ int main(int ac, char **av)
     screenQuad->addComponent(planeMesh);
 
     // Set root object of the scene
-    view.setRootObject(rootEntity);
-    // Show window
+    view.setRootEntity(rootEntity);
     view.show();
 
     return app.exec();
diff --git a/examples/simple-cpp/main.cpp b/examples/simple-cpp/main.cpp
index 44313ebca..3bd32f720 100644
--- a/examples/simple-cpp/main.cpp
+++ b/examples/simple-cpp/main.cpp
@@ -165,7 +165,7 @@ int main(int argc, char* argv[])
 
     rootEntity->addComponent(frameGraph);
 
-    view.setRootObject(rootEntity);
+    view.setRootEntity(rootEntity);
     view.show();
 
     return app.exec();
diff --git a/examples/torus-cpp/main.cpp b/examples/torus-cpp/main.cpp
index a26a9d581..98b457c78 100644
--- a/examples/torus-cpp/main.cpp
+++ b/examples/torus-cpp/main.cpp
@@ -132,8 +132,7 @@ int main(int argc, char **argv)
     rootEntity->addComponent(frameGraph);
 
     // Set root object of the scene
-    view.setRootObject(rootEntity);
-    // Show window
+    view.setRootEntity(rootEntity);
     view.show();
 
     return app.exec();
diff --git a/src/core/aspects/qaspectengine.cpp b/src/core/aspects/qaspectengine.cpp
index dea6987f3..ad7339b20 100644
--- a/src/core/aspects/qaspectengine.cpp
+++ b/src/core/aspects/qaspectengine.cpp
@@ -69,7 +69,7 @@ QAspectEnginePrivate::QAspectEnginePrivate(QAspectEngine *qq)
     m_postman->setScene(m_scene);
     qRegisterMetaType<Qt3D::QAbstractAspect *>();
     qRegisterMetaType<Qt3D::QObserverInterface *>();
-    qRegisterMetaType<Qt3D::QNode *>();
+    qRegisterMetaType<Qt3D::QEntity *>();
     qRegisterMetaType<Qt3D::QSceneInterface *>();
 }
 
@@ -157,18 +157,44 @@ void QAspectEngine::registerAspect(QAbstractAspect *aspect)
                               Q_ARG(Qt3D::QAbstractAspect *, aspect));
 }
 
-void QAspectEngine::setRoot(QNode *rootObject)
+void QAspectEngine::setRootEntity(QEntity *root)
 {
-    Q_D(QAspectEngine);
     qCDebug(Aspects) << "Setting scene root on aspect manager";
-    initNodeTree(rootObject);
+    Q_D(QAspectEngine);
+    if (d->m_root == root)
+        return;
+
+    // Set the new root object. This will cause the old tree to be deleted
+    // and the deletion of the old frontend tree will cause the backends to
+    // free any related resources
+    d->m_root.reset(root);
+
+    // The aspect engine takes ownership of the scene root. We also set the
+    // parent of the scene root to be the engine
+    d->m_root->setParent(this);
+
+    // Prepare the frontend tree for use by giving each node a pointer to the
+    // scene object and adding each node to the scene
+    // TODO: We probably need a call symmetric to this one above in order to
+    // deregister the nodes from the scene
+    initNodeTree(root);
+
+    // Finally, tell the aspects about the new scene object tree. This is done
+    // in a blocking manner to allow the backends to get synchronized before the
+    // main thread starts triggering potentially more notifications
     QMetaObject::invokeMethod(d->m_aspectThread->aspectManager(),
-                              "setRoot",
+                              "setRootEntity",
                               Qt::BlockingQueuedConnection,
-                              Q_ARG(Qt3D::QNode *, rootObject));
+                              Q_ARG(Qt3D::QEntity *, root));
     qCDebug(Aspects) << "Done setting scene root on aspect manager";
 }
 
+QSharedPointer<QEntity> QAspectEngine::rootEntity() const
+{
+    Q_D(const QAspectEngine);
+    return d->m_root;
+}
+
 } // namespace Qt3D
 
 QT_END_NAMESPACE
diff --git a/src/core/aspects/qaspectengine.h b/src/core/aspects/qaspectengine.h
index 96332517e..49d984ef1 100644
--- a/src/core/aspects/qaspectengine.h
+++ b/src/core/aspects/qaspectengine.h
@@ -52,10 +52,11 @@ class QSurface;
 
 namespace Qt3D {
 
-class QNode;
 class QAbstractAspect;
 class QAspectThread;
 class QAspectEnginePrivate;
+class QEntity;
+class QNode;
 
 class QT3DCORESHARED_EXPORT QAspectEngine : public QObject
 {
@@ -66,7 +67,9 @@ public:
     void initialize();
     void shutdown();
 
-    void setRoot(QNode *rootObject);
+    void setRootEntity(QEntity *root);
+    QSharedPointer<QEntity> rootEntity() const;
+
     void setSurface(QSurface *surface);
     void registerAspect(QAbstractAspect *aspect);
 
diff --git a/src/core/aspects/qaspectengine_p.h b/src/core/aspects/qaspectengine_p.h
index a4131ce56..68d0af221 100644
--- a/src/core/aspects/qaspectengine_p.h
+++ b/src/core/aspects/qaspectengine_p.h
@@ -43,14 +43,13 @@
 #define QT3D_QASPECTENGINE_P_H
 
 #include <private/qobject_p.h>
-#include <QMutex>
-#include <QWaitCondition>
-#include <QHash>
+#include <QtCore/qsharedpointer.h>
 
 QT_BEGIN_NAMESPACE
 
 namespace Qt3D {
 
+class QEntity;
 class QNode;
 class QAspectEngine;
 class QAspectThread;
@@ -67,6 +66,7 @@ public:
     QAspectThread *m_aspectThread;
     QPostman *m_postman;
     QSceneInterface *m_scene;
+    QSharedPointer<QEntity> m_root;
 };
 
 } // Qt3D
diff --git a/src/core/aspects/qaspectmanager.cpp b/src/core/aspects/qaspectmanager.cpp
index d6a6d4c21..0e7da01f6 100644
--- a/src/core/aspects/qaspectmanager.cpp
+++ b/src/core/aspects/qaspectmanager.cpp
@@ -101,15 +101,10 @@ void QAspectManager::shutdown()
     qDeleteAll(m_aspects);
 }
 
-void QAspectManager::setRoot(QNode *rootObject)
+void QAspectManager::setRootEntity(Qt3D::QEntity *root)
 {
     qCDebug(Aspects) << Q_FUNC_INFO;
 
-    QEntity *root = qobject_cast<QEntity *>(rootObject);
-
-    if (!root)
-        qWarning() << "Root object is not an Entity";
-
     if (root == m_root)
         return;
 
diff --git a/src/core/aspects/qaspectmanager_p.h b/src/core/aspects/qaspectmanager_p.h
index 9be4423b4..7fccab637 100644
--- a/src/core/aspects/qaspectmanager_p.h
+++ b/src/core/aspects/qaspectmanager_p.h
@@ -72,7 +72,7 @@ public Q_SLOTS:
     void initialize();
     void shutdown();
 
-    void setRoot(Qt3D::QNode *rootObject);
+    void setRootEntity(Qt3D::QEntity *root);
     void setSurface(QSurface *surface);
     void registerAspect(Qt3D::QAbstractAspect *aspect);
     QSurface *surface() const;
diff --git a/src/core/window.cpp b/src/core/window.cpp
index 5d6ee003a..c09a138d9 100644
--- a/src/core/window.cpp
+++ b/src/core/window.cpp
@@ -105,17 +105,9 @@ void Window::onUpdate()
     m_controller->update(1.0 / 60.0);
 }
 
-void Window::setRootObject( QObject* obj )
+void Window::setRootEntity(QEntity *root)
 {
-    if (m_root == obj)
-        return;
-
-    if (obj) {
-        obj->setParent( this );
-        m_root = QSharedPointer<QObject>(obj);
-    }
-
-    m_aspectEngine->setRoot(qobject_cast<QNode *>(obj));
+    m_aspectEngine->setRootEntity(root);
 
     // Hook up controller input to camera
     // TODO: Do this more generically as we may want keyboard ot control an Entity etc
diff --git a/src/core/window.h b/src/core/window.h
index 4fbb0ebf0..9bc12b6f3 100644
--- a/src/core/window.h
+++ b/src/core/window.h
@@ -54,6 +54,7 @@ namespace Qt3D {
 class QAbstractAspect;
 class QAspectEngine;
 class QCamera;
+class QEntity;
 
 // temporary solution to get control over camera
 class CameraController;
@@ -65,11 +66,10 @@ public:
     explicit Window(QScreen *screen = 0);
     ~Window();
 
-    void setRootObject( QObject* obj );
+    void setRootEntity(QEntity *root);
 
-    QSharedPointer<QObject> rootObject() { return m_root; }
-    void    registerAspect(QAbstractAspect *aspect);
-    virtual void    setCamera(QCamera *camera);
+    void registerAspect(QAbstractAspect *aspect);
+    virtual void setCamera(QCamera *camera);
 
 protected:
     virtual void keyPressEvent(QKeyEvent *e);
@@ -85,10 +85,6 @@ private Q_SLOTS:
     void onUpdate();
 
 protected:
-    QSharedPointer<QObject> m_root;
-
-    // The various aspects (subsystems) that will be interested in (parts)
-    // of the objects in the object tree.
     QAspectEngine *m_aspectEngine;
     QCamera* m_camera;
 
diff --git a/src/quick3d/quick3d/quickwindow.cpp b/src/quick3d/quick3d/quickwindow.cpp
index d19845440..d7c55f111 100644
--- a/src/quick3d/quick3d/quickwindow.cpp
+++ b/src/quick3d/quick3d/quickwindow.cpp
@@ -41,12 +41,14 @@
 
 #include "quickwindow.h"
 #include <Qt3DCore/qaspectengine.h>
+#include <Qt3DCore/qentity.h>
+#include <Qt3DCore/cameracontroller.h>
 
 #include <QQmlComponent>
 #include <QQmlContext>
+
 #include <QDebug>
 #include <QTimer>
-#include <Qt3DCore/cameracontroller.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -88,11 +90,9 @@ void QuickWindow::setSource(const QUrl& source)
         return;
     }
 
-    if (m_root) {
-        m_aspectEngine->shutdown();
-        m_aspectEngine->setRoot(0);
-        m_root = QSharedPointer<QObject>();
-    }
+    // If the engine already has a scene object tree, tidy up first
+    if (m_aspectEngine->rootEntity())
+        m_aspectEngine->setRootEntity(Q_NULLPTR);
 
     if (m_component)
         m_component = QSharedPointer<QQmlComponent>();
@@ -156,7 +156,12 @@ void QuickWindow::continueExecute()
         return;
     }
 
-    setRootObject(obj);
+    QEntity *rootEntity = qobject_cast<QEntity *>(obj);
+    if (rootEntity)
+        setRootEntity(rootEntity);
+    else
+        delete obj;
+
     emit statusChanged(status());
 }