Add hook to set QNode parent when creating a QNode in QML

Just need to be a little careful in QNode::setParent() and the
helper in case the qml engine sets a QObject parent but QNode
doesn't know about it yet.

Task-number: QTBUG-47055
Change-Id: I30269bd230ee6eacd2816282fd48f879cfb7c83a
Reviewed-by: Kevin Ottens <kevin.ottens@kdab.com>

2 files changed, 43 insertions, 2 deletions

diff --git a/src/core/nodes/qnode.cpp b/src/core/nodes/qnode.cpp
index 4cdd9ca7b..871eaed39 100644
--- a/src/core/nodes/qnode.cpp
+++ b/src/core/nodes/qnode.cpp
@@ -115,6 +115,10 @@ void QNodePrivate::init(QNode *parent)
 void QNodePrivate::notifyCreationChange()
 {
     Q_Q(QNode);
+    // Do nothing if we already have already sent a node creation change
+    // and not a subsequent node destroyed change.
+    if (m_hasBackendNode)
+        return;
     QNodeCreatedChangeGenerator generator(q);
     const auto creationChanges = generator.creationChanges();
     for (const auto &change : creationChanges)
@@ -265,6 +269,13 @@ void QNodePrivate::_q_setParentHelper(QNode *parent)
     Q_Q(QNode);
     QNode *oldParentNode = q->parentNode();
 
+    // We may get the situation where the QML engine has set the QObject
+    // parent but we have not yet set up the QNode parent requirements.
+    // This check handles this and means we propagate the scene and arbiter
+    // from the parent in the code below.
+    const bool needsSceneInit = !oldParentNode
+            || (oldParentNode && m_parentId != oldParentNode->id());
+
     // If we had a parent, we let him know that we are about to change
     // parent
     if (oldParentNode) {
@@ -283,7 +294,7 @@ void QNodePrivate::_q_setParentHelper(QNode *parent)
     if (newParentNode) {
         // If we had no parent but are about to set one,
         // we need to send a QNodeCreatedChange
-        if (!oldParentNode) {
+        if (needsSceneInit) {
             QNodePrivate *newParentPrivate = QNodePrivate::get(newParentNode);
 
             // Set the scene helper / arbiter
@@ -696,7 +707,10 @@ bool QNode::blockNotifications(bool block)
 void QNode::setParent(QNode *parent)
 {
     Q_D(QNode);
-    if (parentNode() == parent)
+
+    // If we already have a parent don't do anything. Be careful to ensure
+    // that QNode knows about the parent, not just QObject (by checking the ids)
+    if (parentNode() == parent && d->m_parentId == parentNode()->id())
         return;
     d->_q_setParentHelper(parent);
 
diff --git a/src/quick3d/quick3d/qt3dquick_global.cpp b/src/quick3d/quick3d/qt3dquick_global.cpp
index 78523aa4a..f25aae268 100644
--- a/src/quick3d/quick3d/qt3dquick_global.cpp
+++ b/src/quick3d/quick3d/qt3dquick_global.cpp
@@ -669,12 +669,39 @@ static Quick3DColorProvider *getColorProvider()
     return &colorProvider;
 }
 
+static QQmlPrivate::AutoParentResult qquick3ditem_autoParent(QObject *obj, QObject *parent)
+{
+    // When setting a parent (especially during dynamic object creation) in QML,
+    // also try to set up the analogous item/window relationship.
+    auto parentNode = qmlobject_cast<Qt3DCore::QNode *>(parent);
+    if (parentNode) {
+        auto node = qmlobject_cast<Qt3DCore::QNode *>(obj);
+        if (node) {
+            // A QNode has another QNode child
+            node->setParent(parentNode);
+            return QQmlPrivate::Parented;
+        }
+    } else {
+        return QQmlPrivate::IncompatibleParent;
+    }
+    return QQmlPrivate::IncompatibleObject;
+}
+
 void Quick3D_initialize()
 {
     Qt3DCore::Quick::Quick3DValueTypes::registerValueTypes();
     QQml_addValueTypeProvider(getValueTypeProvider());
     QQml_setColorProvider(getColorProvider());
     QAbstractNodeFactory::registerNodeFactory(QuickNodeFactory::instance());
+
+    // Register a hook called when we do component.create() that sets the
+    // parent. We need this as QObject::setParent() is insufficient to propagate
+    // the arbiter and scene to the children (see QNode::setParent(QNode *).
+    // TODO: Replace this with virtual void QObjectPrivate::setParent(QObject *)
+    // that can be called from QObject ctor and QObject::setParent(). That would
+    // allow removal of this hook here and in QtQuick.
+    QQmlPrivate::RegisterAutoParent autoparent = { 0, &qquick3ditem_autoParent };
+    QQmlPrivate::qmlregister(QQmlPrivate::AutoParentRegistration, &autoparent);
 }
 
 void Quick3D_registerType(const char *className, const char *quickName, int major, int minor)