Add accessor to retrieve frontend node from an id

Useful later to sync backend changes back to the frontend.

Change-Id: I874d140fc97462b8e186b66c882647db26d5678e
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>

src/core/aspects/qaspectmanager.cpp

@@ -62,6 +62,7 @@
 #include <Qt3DCore/private/qtickclockservice_p.h>
 #include <Qt3DCore/private/qnodevisitor_p.h>
 #include <Qt3DCore/private/qnode_p.h>
+#include <Qt3DCore/private/qscene_p.h>
 
 #include <QtCore/QCoreApplication>
 
@@ -379,6 +380,24 @@ void QAspectManager::setPostConstructorInit(NodePostConstructorInit *postConstru
     m_postConstructorInit = postConstructorInit;
 }
 
+QNode *QAspectManager::lookupNode(QNodeId id) const
+{
+    if (!m_root)
+        return nullptr;
+
+    QNodePrivate *d = QNodePrivate::get(m_root);
+    return d->m_scene ? d->m_scene->lookupNode(id) : nullptr;
+}
+
+QVector<QNode *> QAspectManager::lookupNodes(const QVector<QNodeId> &ids) const
+{
+    if (!m_root)
+        return {};
+
+    QNodePrivate *d = QNodePrivate::get(m_root);
+    return d->m_scene ? d->m_scene->lookupNodes(ids) : QVector<QNode *>{};
+}
+
 /*!
     \internal
     \brief Drives the Qt3D simulation loop in the main thread

src/core/aspects/qaspectmanager_p.h

@@ -108,6 +108,9 @@ public:
     QServiceLocator *serviceLocator() const;
     void setPostConstructorInit(NodePostConstructorInit *postConstructorInit);
 
+    QNode *lookupNode(QNodeId id) const;
+    QVector<QNode *> lookupNodes(const QVector<QNodeId> &ids) const;
+
 private:
     bool event(QEvent *event) override;
     void requestNextFrame();