Fix Entity parenting hierarchy

When the initial Entity backend node hierarchy is created it skips over
any non-entity nodes to ensure that Entities are only parented to
other Entities. Calling QNode::setParent breaks this when reparenting
Entities to non-entity nodes.

Fix by sending a new "parentEntityUpdated" property update that backend
Entity nodes listen for. They keep the id of their new parent and flag
the need to rebuild the entity hierarchy.  This triggers a new job to
clear the children and parents of every backend Entity, then rebuilds
the hierarchy using the stored parent ID in each Entity. This is much
more forgiving of creation/parenting ordering issues and shouldn't be
less performant because any Entity reparent was previously marking
everything dirty anyway.

Add a new test from QTBUG-73905 that creates 4 cylinders and manipulates
the parents in different ways.

Add a new test to tst_nodes to reparent a QEntity to a QNode and ensure
the entity finds it's correct QEntity parent.

Add a new test to tst_entity to ensure backend nodes correctly handle
the new parenting events.

Task-number: QTBUG-73905
Change-Id: Iab0203947d89bbed2868b3629fbde879675fe568
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>

13 files changed, 503 insertions, 1 deletions

diff --git a/tests/auto/core/nodes/tst_nodes.cpp b/tests/auto/core/nodes/tst_nodes.cpp
index 3f7fb4a75..193d88c83 100644
--- a/tests/auto/core/nodes/tst_nodes.cpp
+++ b/tests/auto/core/nodes/tst_nodes.cpp
@@ -81,6 +81,7 @@ private slots:
     void removingChildEntitiesFromNode();
 
     void checkConstructionSetParentMix(); // QTBUG-60612
+    void checkParentingQEntityToQNode(); // QTBUG-73905
     void checkConstructionWithParent();
     void checkConstructionWithNonRootParent(); // QTBUG-73986
     void checkConstructionAsListElement();
@@ -1079,6 +1080,72 @@ void tst_Nodes::checkConstructionSetParentMix()
     QCOMPARE(lastEvent->addedNodeId(), subTreeRoot->id());
 }
 
+void tst_Nodes::checkParentingQEntityToQNode()
+{
+    // GIVEN
+    ObserverSpy spy;
+    Qt3DCore::QScene scene;
+    QScopedPointer<MyQNode> root(new MyQNode());
+
+    // WHEN
+    root->setArbiterAndScene(&spy, &scene);
+    root->setSimulateBackendCreated(true);
+
+    // THEN
+    QVERIFY(Qt3DCore::QNodePrivate::get(root.data())->scene() != nullptr);
+
+    // WHEN
+    auto subTreeRoot = new Qt3DCore::QEntity(root.data());
+    auto childEntity = new Qt3DCore::QEntity(subTreeRoot);
+    auto childNode = new Qt3DCore::QNode(subTreeRoot);
+
+    // THEN
+    QCoreApplication::processEvents();
+
+    // Ensure first event is subTreeRoot creation
+    const Qt3DCore::QNodeCreatedChangeBasePtr firstEvent = spy.events.takeFirst().change().dynamicCast<Qt3DCore::QNodeCreatedChangeBase>();
+    QVERIFY(!firstEvent.isNull());
+    QCOMPARE(firstEvent->subjectId(), subTreeRoot->id());
+    QCOMPARE(firstEvent->parentId(), root->id());
+
+    // Ensure 2nd event is childEntity creation
+    const Qt3DCore::QNodeCreatedChangeBasePtr secondEvent = spy.events.takeFirst().change().dynamicCast<Qt3DCore::QNodeCreatedChangeBase>();
+    QVERIFY(!secondEvent.isNull());
+    QCOMPARE(secondEvent->subjectId(), childEntity->id());
+    QCOMPARE(secondEvent->parentId(), subTreeRoot->id());
+
+    // Ensure 3rd event is childNode creation
+    const Qt3DCore::QNodeCreatedChangeBasePtr thirdEvent = spy.events.takeFirst().change().dynamicCast<Qt3DCore::QNodeCreatedChangeBase>();
+    QVERIFY(!thirdEvent.isNull());
+    QCOMPARE(thirdEvent->subjectId(), childNode->id());
+    QCOMPARE(thirdEvent->parentId(), subTreeRoot->id());
+
+
+    // WHEN we reparent the childEntity to the childNode (QNode)
+
+    spy.events.clear();
+    childEntity->setParent(childNode);
+    // THEN we should get
+    // - one child removed change for childEntity->subTreeRoot,
+    // - one child added change for childEntity->childNode,
+    // - and one property updated event specifying the correct QEntity parent (subTreeRoot)
+    QCOMPARE(spy.events.size(), 3);
+
+    const auto removedEvent = spy.events.takeFirst().change().dynamicCast<Qt3DCore::QPropertyNodeRemovedChange>();
+    QVERIFY(!removedEvent.isNull());
+    QCOMPARE(removedEvent->subjectId(), subTreeRoot->id());
+
+    const auto addedEvent = spy.events.takeFirst().change().dynamicCast<Qt3DCore::QPropertyNodeAddedChange>();
+    QVERIFY(!addedEvent.isNull());
+    QCOMPARE(addedEvent->subjectId(), childNode->id());
+
+    const auto parentChangeEvent = spy.events.takeFirst().change().dynamicCast<Qt3DCore::QPropertyUpdatedChange>();
+    QVERIFY(!parentChangeEvent.isNull());
+    QCOMPARE(parentChangeEvent->subjectId(), childEntity->id());
+    QCOMPARE(parentChangeEvent->propertyName(), "parentEntityUpdated");
+    QCOMPARE(parentChangeEvent->value().value<Qt3DCore::QNodeId>(), subTreeRoot->id());
+}
+
 void tst_Nodes::checkConstructionWithParent()
 {
     // GIVEN
diff --git a/tests/auto/render/boundingsphere/tst_boundingsphere.cpp b/tests/auto/render/boundingsphere/tst_boundingsphere.cpp
index 992e643d2..b35c6d31a 100644
--- a/tests/auto/render/boundingsphere/tst_boundingsphere.cpp
+++ b/tests/auto/render/boundingsphere/tst_boundingsphere.cpp
@@ -55,6 +55,7 @@
 #include <Qt3DRender/private/calcboundingvolumejob_p.h>
 #include <Qt3DRender/private/calcgeometrytrianglevolumes_p.h>
 #include <Qt3DRender/private/loadbufferjob_p.h>
+#include <Qt3DRender/private/updateentityhierarchyjob_p.h>
 #include <Qt3DRender/private/buffermanager_p.h>
 #include <Qt3DRender/private/geometryrenderermanager_p.h>
 #include <Qt3DRender/private/sphere_p.h>
@@ -116,6 +117,10 @@ namespace {
 
 void runRequiredJobs(Qt3DRender::TestAspect *test)
 {
+    Qt3DRender::Render::UpdateEntityHierarchyJob updateEntitiesJob;
+    updateEntitiesJob.setManager(test->nodeManagers());
+    updateEntitiesJob.run();
+
     Qt3DRender::Render::UpdateWorldTransformJob updateWorldTransform;
     updateWorldTransform.setRoot(test->sceneRoot());
     updateWorldTransform.run();
diff --git a/tests/auto/render/entity/tst_entity.cpp b/tests/auto/render/entity/tst_entity.cpp
index 6ad958451..123a648d6 100644
--- a/tests/auto/render/entity/tst_entity.cpp
+++ b/tests/auto/render/entity/tst_entity.cpp
@@ -151,7 +151,7 @@ private slots:
         QVERIFY(!entity.componentsUuid<EnvironmentLight>().isEmpty());
         QVERIFY(!entity.componentUuid<Armature>().isNull());
         QVERIFY(entity.isBoundingVolumeDirty());
-        QVERIFY(!entity.childrenHandles().isEmpty());
+        QVERIFY(entity.childrenHandles().isEmpty());
         QVERIFY(!entity.layerIds().isEmpty());
         QVERIFY(renderer.dirtyBits() != 0);
         bool containsAll = entity.containsComponentsOfType<Transform,
@@ -162,6 +162,7 @@ private slots:
         entity.cleanup();
 
         // THEN
+        QVERIFY(entity.parentEntityId().isNull());
         QVERIFY(entity.componentUuid<Transform>().isNull());
         QVERIFY(entity.componentUuid<CameraLens>().isNull());
         QVERIFY(entity.componentUuid<Material>().isNull());
@@ -180,6 +181,122 @@ private slots:
         QVERIFY(!containsAll);
     }
 
+    void checkRebuildingEntityHierarchy()
+    {
+        // GIVEN
+        TestRenderer renderer;
+        NodeManagers nodeManagers;
+        Qt3DCore::QEntity frontendEntityA, frontendEntityB, frontendEntityC;
+
+        auto entityCreator = [&nodeManagers, &renderer](const Qt3DCore::QEntity &frontEndEntity) {
+            Entity *entity = nodeManagers.renderNodesManager()->getOrCreateResource(frontEndEntity.id());
+            entity->setNodeManagers(&nodeManagers);
+            entity->setRenderer(&renderer);
+            return entity;
+        };
+
+        auto backendA = entityCreator(frontendEntityA);
+        auto backendB = entityCreator(frontendEntityB);
+        auto backendC = entityCreator(frontendEntityC);
+
+        // THEN
+        QVERIFY(backendA->parentEntityId().isNull());
+        QVERIFY(backendB->parentEntityId().isNull());
+        QVERIFY(backendC->parentEntityId().isNull());
+
+        QVERIFY(backendA->parent() == nullptr);
+        QVERIFY(backendB->parent() == nullptr);
+        QVERIFY(backendC->parent() == nullptr);
+
+        QVERIFY(backendA->childrenHandles().isEmpty());
+        QVERIFY(backendB->childrenHandles().isEmpty());
+        QVERIFY(backendC->childrenHandles().isEmpty());
+
+        // WHEN
+        renderer.clearDirtyBits(0);
+        QVERIFY(renderer.dirtyBits() == 0);
+
+        auto sendParentChange = [&nodeManagers](const Qt3DCore::QEntity &entity) {
+            const auto parentChange = QPropertyUpdatedChangePtr::create(entity.id());
+            parentChange->setPropertyName("parentEntityUpdated");
+            auto parent = entity.parentEntity();
+            parentChange->setValue(QVariant::fromValue(parent ? parent->id() : Qt3DCore::QNodeId()));
+
+            Entity *backendEntity = nodeManagers.renderNodesManager()->getOrCreateResource(entity.id());
+            backendEntity->sceneChangeEvent(parentChange);
+        };
+
+        // reparent B to A and C to B.
+        frontendEntityB.setParent(&frontendEntityA);
+        sendParentChange(frontendEntityB);
+        frontendEntityC.setParent(&frontendEntityB);
+        sendParentChange(frontendEntityC);
+
+        // THEN
+        QVERIFY(renderer.dirtyBits() & AbstractRenderer::EntityHierarchyDirty);
+
+        QVERIFY(backendA->parentEntityId().isNull());
+        QVERIFY(backendB->parentEntityId() == frontendEntityA.id());
+        QVERIFY(backendC->parentEntityId() == frontendEntityB.id());
+
+        QVERIFY(backendA->parent() == nullptr);
+        QVERIFY(backendB->parent() == nullptr);
+        QVERIFY(backendC->parent() == nullptr);
+
+        QVERIFY(backendA->childrenHandles().isEmpty());
+        QVERIFY(backendB->childrenHandles().isEmpty());
+        QVERIFY(backendC->childrenHandles().isEmpty());
+
+        // WHEN
+        auto rebuildHierarchy = [](Entity *backend) {
+            backend->clearEntityHierarchy();
+            backend->rebuildEntityHierarchy();
+        };
+        rebuildHierarchy(backendA);
+        rebuildHierarchy(backendB);
+        rebuildHierarchy(backendC);
+
+        // THEN
+        QVERIFY(backendA->parent() == nullptr);
+        QVERIFY(backendB->parent() == backendA);
+        QVERIFY(backendC->parent() == backendB);
+
+        QVERIFY(!backendA->childrenHandles().isEmpty());
+        QVERIFY(!backendB->childrenHandles().isEmpty());
+        QVERIFY(backendC->childrenHandles().isEmpty());
+
+        // WHEN - reparent B to null.
+        frontendEntityB.setParent(static_cast<Qt3DCore::QNode *>(nullptr));
+        sendParentChange(frontendEntityB);
+        rebuildHierarchy(backendA);
+        rebuildHierarchy(backendB);
+        rebuildHierarchy(backendC);
+
+        QVERIFY(backendA->parentEntityId().isNull());
+        QVERIFY(backendB->parentEntityId().isNull());
+        QVERIFY(backendC->parentEntityId() == frontendEntityB.id());
+
+        QVERIFY(backendA->parent() == nullptr);
+        QVERIFY(backendB->parent() == nullptr);
+        QVERIFY(backendC->parent() == backendB);
+
+        QVERIFY(backendA->childrenHandles().isEmpty());
+        QVERIFY(!backendB->childrenHandles().isEmpty());
+        QVERIFY(backendC->childrenHandles().isEmpty());
+
+        // WHEN - cleanup
+        backendA->cleanup();
+        backendB->cleanup();
+        backendC->cleanup();
+
+        // THEN
+        QVERIFY(backendA->parentEntityId().isNull());
+        QVERIFY(backendB->parentEntityId().isNull());
+        QVERIFY(backendC->parentEntityId().isNull());
+
+        QVERIFY(renderer.dirtyBits() != 0);
+    }
+
     void shouldHandleSingleComponentEvents_data()
     {
         QTest::addColumn<QComponent*>("component");
diff --git a/tests/auto/render/layerfiltering/tst_layerfiltering.cpp b/tests/auto/render/layerfiltering/tst_layerfiltering.cpp
index eeffc69b2..9b8636f49 100644
--- a/tests/auto/render/layerfiltering/tst_layerfiltering.cpp
+++ b/tests/auto/render/layerfiltering/tst_layerfiltering.cpp
@@ -33,6 +33,7 @@
 #include <Qt3DRender/private/entity_p.h>
 #include <Qt3DRender/private/filterlayerentityjob_p.h>
 #include <Qt3DRender/private/updatetreeenabledjob_p.h>
+#include <Qt3DRender/private/updateentityhierarchyjob_p.h>
 #include <Qt3DRender/qlayer.h>
 #include <Qt3DRender/qlayerfilter.h>
 #include "testaspect.h"
@@ -632,6 +633,11 @@ private Q_SLOTS:
 
         // WHEN
         Qt3DRender::Render::Entity *backendRoot = aspect->nodeManagers()->renderNodesManager()->getOrCreateResource(entitySubtree->id());
+
+        Qt3DRender::Render::UpdateEntityHierarchyJob updateEntitiesJob;
+        updateEntitiesJob.setManager(aspect->nodeManagers());
+        updateEntitiesJob.run();
+
         Qt3DRender::Render::UpdateTreeEnabledJob updateTreeEnabledJob;
         updateTreeEnabledJob.setRoot(backendRoot);
         updateTreeEnabledJob.run();
diff --git a/tests/auto/render/pickboundingvolumejob/tst_pickboundingvolumejob.cpp b/tests/auto/render/pickboundingvolumejob/tst_pickboundingvolumejob.cpp
index 60b60eb6e..21f75b7a4 100644
--- a/tests/auto/render/pickboundingvolumejob/tst_pickboundingvolumejob.cpp
+++ b/tests/auto/render/pickboundingvolumejob/tst_pickboundingvolumejob.cpp
@@ -47,6 +47,7 @@
 #include <Qt3DRender/private/qrenderaspect_p.h>
 #include <Qt3DRender/private/pickboundingvolumejob_p.h>
 #include <Qt3DRender/private/pickboundingvolumeutils_p.h>
+#include <Qt3DRender/private/updateentityhierarchyjob_p.h>
 #include <Qt3DRender/private/updatemeshtrianglelistjob_p.h>
 #include <Qt3DRender/private/updateworldboundingvolumejob_p.h>
 #include <Qt3DRender/private/updateworldtransformjob_p.h>
@@ -107,6 +108,10 @@ namespace {
 
 void runRequiredJobs(Qt3DRender::TestAspect *test)
 {
+    Qt3DRender::Render::UpdateEntityHierarchyJob updateEntitiesJob;
+    updateEntitiesJob.setManager(test->nodeManagers());
+    updateEntitiesJob.run();
+
     Qt3DRender::Render::UpdateWorldTransformJob updateWorldTransform;
     updateWorldTransform.setRoot(test->sceneRoot());
     updateWorldTransform.run();
@@ -252,6 +257,10 @@ private Q_SLOTS:
         QVERIFY(root);
         QScopedPointer<Qt3DRender::TestAspect> test(new Qt3DRender::TestAspect(root.data()));
 
+        Qt3DRender::Render::UpdateEntityHierarchyJob updateEntitiesJob;
+        updateEntitiesJob.setManager(test->nodeManagers());
+        updateEntitiesJob.run();
+
         // THEN
         QList<Qt3DCore::QEntity *> frontendEntities;
         frontendEntities << qobject_cast<Qt3DCore::QEntity *>(root.data()) << root->findChildren<Qt3DCore::QEntity *>();
diff --git a/tests/auto/render/proximityfiltering/tst_proximityfiltering.cpp b/tests/auto/render/proximityfiltering/tst_proximityfiltering.cpp
index 7a5648271..7bb3c16a7 100644
--- a/tests/auto/render/proximityfiltering/tst_proximityfiltering.cpp
+++ b/tests/auto/render/proximityfiltering/tst_proximityfiltering.cpp
@@ -246,6 +246,11 @@ private Q_SLOTS:
 
         // WHEN
         Qt3DRender::Render::Entity *backendRoot = aspect->nodeManagers()->renderNodesManager()->getOrCreateResource(entitySubtree->id());
+
+        Qt3DRender::Render::UpdateEntityHierarchyJob updateEntitiesJob;
+        updateEntitiesJob.setManager(aspect->nodeManagers());
+        updateEntitiesJob.run();
+
         Qt3DRender::Render::UpdateTreeEnabledJob updateTreeEnabledJob;
         updateTreeEnabledJob.setRoot(backendRoot);
         updateTreeEnabledJob.run();
diff --git a/tests/auto/render/qcamera/tst_qcamera.cpp b/tests/auto/render/qcamera/tst_qcamera.cpp
index b630c447a..7aef2af7d 100644
--- a/tests/auto/render/qcamera/tst_qcamera.cpp
+++ b/tests/auto/render/qcamera/tst_qcamera.cpp
@@ -35,6 +35,7 @@
 
 #include <Qt3DCore/QEntity>
 #include <Qt3DCore/private/qnodecreatedchangegenerator_p.h>
+#include <Qt3DRender/private/updateentityhierarchyjob_p.h>
 #include <Qt3DCore/private/qaspectjobmanager_p.h>
 #include <Qt3DCore/qpropertyupdatedchange.h>
 #include <Qt3DCore/qnodecreatedchange.h>
@@ -99,6 +100,10 @@ namespace {
 
 void runRequiredJobs(Qt3DRender::TestAspect *test)
 {
+    Qt3DRender::Render::UpdateEntityHierarchyJob updateEntitiesJob;
+    updateEntitiesJob.setManager(test->nodeManagers());
+    updateEntitiesJob.run();
+
     Qt3DRender::Render::UpdateWorldTransformJob updateWorldTransform;
     updateWorldTransform.setRoot(test->sceneRoot());
     updateWorldTransform.run();
diff --git a/tests/auto/render/raycastingjob/tst_raycastingjob.cpp b/tests/auto/render/raycastingjob/tst_raycastingjob.cpp
index 4980bfc30..411bb9160 100644
--- a/tests/auto/render/raycastingjob/tst_raycastingjob.cpp
+++ b/tests/auto/render/raycastingjob/tst_raycastingjob.cpp
@@ -51,6 +51,7 @@
 #include <Qt3DRender/private/updateworldtransformjob_p.h>
 #include <Qt3DRender/private/expandboundingvolumejob_p.h>
 #include <Qt3DRender/private/calcboundingvolumejob_p.h>
+#include <Qt3DRender/private/updateentityhierarchyjob_p.h>
 #include <Qt3DRender/private/calcgeometrytrianglevolumes_p.h>
 #include <Qt3DRender/private/loadbufferjob_p.h>
 #include <Qt3DRender/private/buffermanager_p.h>
@@ -106,6 +107,10 @@ namespace {
 
 void runRequiredJobs(Qt3DRender::TestAspect *test)
 {
+    Qt3DRender::Render::UpdateEntityHierarchyJob updateEntitiesJob;
+    updateEntitiesJob.setManager(test->nodeManagers());
+    updateEntitiesJob.run();
+
     Qt3DRender::Render::UpdateWorldTransformJob updateWorldTransform;
     updateWorldTransform.setRoot(test->sceneRoot());
     updateWorldTransform.run();
diff --git a/tests/auto/render/renderer/tst_renderer.cpp b/tests/auto/render/renderer/tst_renderer.cpp
index 9321f5303..e67e0ed55 100644
--- a/tests/auto/render/renderer/tst_renderer.cpp
+++ b/tests/auto/render/renderer/tst_renderer.cpp
@@ -252,6 +252,30 @@ private Q_SLOTS:
         renderQueue->reset();
 
         // WHEN
+        renderer.markDirty(Qt3DRender::Render::AbstractRenderer::EntityHierarchyDirty, nullptr);
+        jobs = renderer.renderBinJobs();
+
+        // THEN
+        QCOMPARE(jobs.size(),
+                 1 + // EntityEnabledDirty
+                 1 + // EntityHierarchyJob
+                 1 + // WorldTransformJob
+                 1 + // UpdateWorldBoundingVolume
+                 1 + // UpdateShaderDataTransform
+                 1 + // ExpandBoundingVolumeJob
+                 1 + // CalculateBoundingVolumeJob
+                 1 + // UpdateEntityLayersJob
+                 1 + // updateLevelOfDetailJob
+                 1 + // updateSkinningPaletteJob
+                 1 + // cleanupJob
+                 1 + // sendBufferCaptureJob
+                 singleRenderViewJobCount +
+                 layerCacheJobCount);
+
+        renderer.clearDirtyBits(Qt3DRender::Render::AbstractRenderer::AllDirty);
+        renderQueue->reset();
+
+        // WHEN
         renderer.markDirty(Qt3DRender::Render::AbstractRenderer::AllDirty, nullptr);
         jobs = renderer.renderBinJobs();
 
@@ -259,6 +283,7 @@ private Q_SLOTS:
         // and ShaderGathererJob are not added here)
         QCOMPARE(jobs.size(),
                  1 + // EntityEnabledDirty
+                 1 + // EntityHierarchyDirty
                  1 + // WorldTransformJob
                  1 + // UpdateWorldBoundingVolume
                  1 + // UpdateShaderDataTransform
diff --git a/tests/auto/render/updateshaderdatatransformjob/tst_updateshaderdatatransformjob.cpp b/tests/auto/render/updateshaderdatatransformjob/tst_updateshaderdatatransformjob.cpp
index 67ddccd9b..4bab46423 100644
--- a/tests/auto/render/updateshaderdatatransformjob/tst_updateshaderdatatransformjob.cpp
+++ b/tests/auto/render/updateshaderdatatransformjob/tst_updateshaderdatatransformjob.cpp
@@ -29,6 +29,7 @@
 #include <QtTest/QTest>
 #include <Qt3DRender/private/updateshaderdatatransformjob_p.h>
 #include <Qt3DRender/private/updateworldtransformjob_p.h>
+#include <Qt3DRender/private/updateentityhierarchyjob_p.h>
 #include <Qt3DRender/private/nodemanagers_p.h>
 #include <Qt3DRender/private/managers_p.h>
 #include <Qt3DRender/qrenderaspect.h>
@@ -88,6 +89,10 @@ namespace {
 
 void runRequiredJobs(Qt3DRender::TestAspect *test)
 {
+    Qt3DRender::Render::UpdateEntityHierarchyJob updateEntitiesJob;
+    updateEntitiesJob.setManager(test->nodeManagers());
+    updateEntitiesJob.run();
+
     Qt3DRender::Render::UpdateWorldTransformJob updateWorldTransform;
     updateWorldTransform.setRoot(test->sceneRoot());
     updateWorldTransform.run();
diff --git a/tests/manual/cylinder-parent-test/cylinder-parent-test.pro b/tests/manual/cylinder-parent-test/cylinder-parent-test.pro
new file mode 100644
index 000000000..d3db3bc76
--- /dev/null
+++ b/tests/manual/cylinder-parent-test/cylinder-parent-test.pro
@@ -0,0 +1,9 @@
+!include( ../manual.pri ) {
+    error( "Couldn't find the manual.pri file!" )
+}
+
+QT += 3dcore 3drender 3dinput 3dextras
+
+SOURCES += main.cpp
+
+
diff --git a/tests/manual/cylinder-parent-test/main.cpp b/tests/manual/cylinder-parent-test/main.cpp
new file mode 100644
index 000000000..823461a28
--- /dev/null
+++ b/tests/manual/cylinder-parent-test/main.cpp
@@ -0,0 +1,243 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 Klaralvdalens Datakonsult AB (KDAB).
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt3D module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QGuiApplication>
+#include <QTimer>
+
+#include <Qt3DInput/QInputAspect>
+
+#include <Qt3DRender/qcamera.h>
+#include <Qt3DRender/qcameralens.h>
+#include <Qt3DExtras/qcylindermesh.h>
+#include <Qt3DRender/qmesh.h>
+#include <Qt3DRender/qtechnique.h>
+#include <Qt3DExtras/qphongmaterial.h>
+#include <Qt3DRender/qeffect.h>
+#include <Qt3DRender/qtexture.h>
+#include <Qt3DRender/qrenderpass.h>
+#include <Qt3DRender/qrenderaspect.h>
+#include <Qt3DExtras/qforwardrenderer.h>
+
+#include <Qt3DCore/qentity.h>
+#include <Qt3DCore/qtransform.h>
+#include <Qt3DCore/qaspectengine.h>
+
+#include <Qt3DExtras/qt3dwindow.h>
+#include <Qt3DExtras/qorbitcameracontroller.h>
+#include <QThread>
+#include <QLoggingCategory>
+
+#include <type_traits>
+
+int main(int argc, char **argv)
+{
+    QGuiApplication app(argc, argv);
+    Qt3DExtras::Qt3DWindow view;
+
+    QLoggingCategory::setFilterRules("Qt3D.Renderer.RenderNodes=true");
+
+    // Root entity
+    Qt3DCore::QEntity *rootEntity = new Qt3DCore::QEntity();
+    view.setRootEntity(rootEntity);
+    rootEntity->setObjectName("Root Entity");
+
+    // Set root object of the scene
+    view.show();
+
+    // Camera
+    Qt3DRender::QCamera *camera = view.camera();
+    camera->lens()->setPerspectiveProjection(45.0f, 16.0f / 9.0f, 0.1f, 1000.0f);
+    camera->setPosition(QVector3D(0, 0, 20.0f));
+    camera->setUpVector(QVector3D(0, 1, 0));
+    camera->setViewCenter(QVector3D(0, 0, 0));
+
+    // For camera controls
+    Qt3DExtras::QOrbitCameraController *cameraController = new Qt3DExtras::QOrbitCameraController(rootEntity);
+    cameraController->setCamera(camera);
+
+    // Cylinder shape data
+    Qt3DExtras::QCylinderMesh *mesh = new Qt3DExtras::QCylinderMesh();
+
+    qDebug() << "Setup complete.  Creating cylinders\n";
+
+    // simple setParent from nullptr (OK for QTBUG-73905)
+    // green cylinder, bottom left
+    {
+        Qt3DCore::QTransform *leftTransform = new Qt3DCore::QTransform;
+        leftTransform->setTranslation(QVector3D(-5, -2, 0));
+        leftTransform->setObjectName("Green transform");
+
+        Qt3DExtras::QPhongMaterial *greenMaterial = new Qt3DExtras::QPhongMaterial(rootEntity);
+        greenMaterial->setObjectName("Green Material");
+        greenMaterial->setDiffuse(Qt::green);
+
+        Qt3DCore::QEntity *grandParentNode = new Qt3DCore::QEntity();
+        Qt3DCore::QEntity *parentNode = new Qt3DCore::QEntity();
+        Qt3DCore::QEntity *leafNode = new Qt3DCore::QEntity();
+        grandParentNode->setObjectName("Green Grandparent");
+        parentNode->setObjectName("Green Parent");
+        leafNode->setObjectName("Green Leaf");
+
+        leafNode->addComponent(mesh);
+        leafNode->addComponent(greenMaterial);
+        parentNode->addComponent(leftTransform);
+
+        grandParentNode->setParent(rootEntity);
+        parentNode->setParent(grandParentNode);
+        leafNode->setParent(parentNode);
+    }
+
+    // simple setParent from rootEntity (doesn't work QTBUG-73905)
+    // yellow cylinder, top left
+    {
+        Qt3DCore::QTransform *leftTransform = new Qt3DCore::QTransform;
+        leftTransform->setTranslation(QVector3D(-5, 2, 0));
+        leftTransform->setObjectName("Yellow Transform");
+
+        Qt3DExtras::QPhongMaterial *yellowMaterial = new Qt3DExtras::QPhongMaterial(rootEntity);
+        yellowMaterial->setObjectName("Yellow Material");
+        yellowMaterial->setDiffuse(Qt::yellow);
+
+        Qt3DCore::QEntity *grandParentNode = new Qt3DCore::QEntity(rootEntity);
+        Qt3DCore::QEntity *parentNode = new Qt3DCore::QEntity(rootEntity);
+        Qt3DCore::QEntity *leafNode = new Qt3DCore::QEntity(rootEntity);
+        leafNode->setObjectName("Yellow Leaf");
+        grandParentNode->setObjectName("Yellow Grandparent");
+        parentNode->setObjectName("Yellow Parent");
+
+        leafNode->addComponent(mesh);
+        leafNode->addComponent(yellowMaterial);
+        parentNode->addComponent(leftTransform);
+
+        // sometimes this can change things
+        //QCoreApplication::processEvents();
+
+        grandParentNode->setParent(rootEntity);
+        parentNode->setParent(grandParentNode);
+        leafNode->setParent(parentNode);
+    }
+
+    // complex setParent from nullptr (OK QTBUG-73905?)
+    // red cylinder, Bottom-right
+    {
+        Qt3DCore::QNode *tree1node1 = new Qt3DCore::QNode();
+        Qt3DCore::QEntity *tree1node2 = new Qt3DCore::QEntity();
+        Qt3DCore::QNode *tree1node3 = new Qt3DCore::QNode();
+        tree1node1->setObjectName("Red Tree1-Node1");
+        tree1node2->setObjectName("Red Tree1-Node2");
+        tree1node3->setObjectName("Red Tree1-Node3");
+
+        Qt3DCore::QNode *tree2node1 = new Qt3DCore::QNode();
+        Qt3DCore::QEntity *tree2node2 = new Qt3DCore::QEntity();
+        Qt3DCore::QNode *tree2node3 = new Qt3DCore::QNode();
+        tree2node1->setObjectName("Red Tree2-Node1");
+        tree2node2->setObjectName("Red Tree2-Node2");
+        tree2node3->setObjectName("Red Tree2-Node3");
+
+        Qt3DCore::QTransform *wrongRedTransform = new Qt3DCore::QTransform;
+        wrongRedTransform->setTranslation(QVector3D(1, -1, 0));
+        Qt3DCore::QTransform *bottomRightTransform = new Qt3DCore::QTransform;
+        bottomRightTransform->setTranslation(QVector3D(5, -2, 0));
+        bottomRightTransform->setObjectName("Red BR Transform");
+        wrongRedTransform->setObjectName("Red Wrong Transform");
+
+        Qt3DExtras::QPhongMaterial *redMaterial = new Qt3DExtras::QPhongMaterial(rootEntity);
+        redMaterial->setDiffuse(Qt::red);
+        redMaterial->setObjectName("Red Material");
+        Qt3DCore::QEntity *leafNode = new Qt3DCore::QEntity();
+        leafNode->setObjectName("Red Leaf");
+        leafNode->addComponent(mesh);
+        leafNode->addComponent(redMaterial);
+
+        tree1node2->addComponent(wrongRedTransform);
+        tree2node2->addComponent(bottomRightTransform);
+
+        tree1node1->setParent(rootEntity);
+        tree1node2->setParent(tree1node1);
+        tree1node3->setParent(tree1node2);
+
+        tree2node1->setParent(rootEntity);
+        tree2node2->setParent(tree2node1);
+        tree2node3->setParent(tree2node2);
+
+        leafNode->setParent(tree1node3);
+        leafNode->setParent(tree2node3);
+    }
+
+    // complex setParent from rootEntity (doesn't work QTBUG-73905)
+    // blue cylinder, top right
+    {
+        Qt3DCore::QNode *tree1node1 = new Qt3DCore::QNode(rootEntity);
+        Qt3DCore::QEntity *tree1node2 = new Qt3DCore::QEntity(rootEntity);
+        Qt3DCore::QNode *tree1node3 = new Qt3DCore::QNode(rootEntity);
+        tree1node1->setObjectName("Blue Tree1-Node1");
+        tree1node2->setObjectName("Blue Tree1-Node2");
+        tree1node3->setObjectName("Blue Tree1-Node3");
+
+        Qt3DCore::QNode *tree2node1 = new Qt3DCore::QNode(rootEntity);
+        Qt3DCore::QEntity *tree2node2 = new Qt3DCore::QEntity(rootEntity);
+        Qt3DCore::QNode *tree2node3 = new Qt3DCore::QNode(rootEntity);
+        tree2node1->setObjectName("Blue Tree2-Node1");
+        tree2node2->setObjectName("Blue Tree2-Node2");
+        tree2node3->setObjectName("Blue Tree2-Node3");
+
+        Qt3DCore::QTransform *wrongBlueTransform = new Qt3DCore::QTransform;
+        wrongBlueTransform->setTranslation(QVector3D(1, 1, 0));
+        Qt3DCore::QTransform *topRightTransform = new Qt3DCore::QTransform;
+        topRightTransform->setTranslation(QVector3D(5, 2, 0));
+        wrongBlueTransform->setObjectName("Blue Wrong Transform");
+        topRightTransform->setObjectName("Blue TR Transform");
+
+        Qt3DExtras::QPhongMaterial *blueMaterial = new Qt3DExtras::QPhongMaterial(rootEntity);
+        blueMaterial->setObjectName("Blue Material");
+        blueMaterial->setDiffuse(Qt::blue);
+        Qt3DCore::QEntity *leafNode = new Qt3DCore::QEntity(rootEntity);
+        leafNode->addComponent(mesh);
+        leafNode->addComponent(blueMaterial);
+        leafNode->setObjectName("Blue Leaf");
+
+        // sometimes this can change things
+        //QCoreApplication::processEvents();
+
+        tree1node2->addComponent(wrongBlueTransform);
+        tree2node2->addComponent(topRightTransform);
+
+        tree1node1->setParent(rootEntity);
+        tree1node2->setParent(tree1node1);
+        tree1node3->setParent(tree1node2);
+
+        tree2node1->setParent(rootEntity);
+        tree2node2->setParent(tree2node1);
+        tree2node3->setParent(tree2node2);
+
+        leafNode->setParent(tree1node3);
+        leafNode->setParent(tree2node3);
+    }
+
+    return app.exec();
+}
diff --git a/tests/manual/manual.pro b/tests/manual/manual.pro
index 6666245ca..4900add69 100644
--- a/tests/manual/manual.pro
+++ b/tests/manual/manual.pro
@@ -13,6 +13,7 @@ SUBDIRS += \
     custom-mesh-update-data-cpp \
     custom-mesh-update-data-qml \
     cylinder-cpp \
+    cylinder-parent-test \
     cylinder-qml \
     deferred-renderer-cpp \
     deferred-renderer-qml \