[Interest] [Qt3D] Crash while instantiating custom geometry

[ORRU' Carlo (MM)]

Hi all,

For a project I'm working on I need to create 3D objects whose geometry depends on data coming from an external input line:
so, to test the whole mechanism, I'm trying to use Qt3D to spawn objects with custom geometry inside an event triggered by a timer.
I tried using both Qt v5.6.1 and Qt v5.7.0 and I got different (and, in my opinion, odd) behaviours.

Here is my QML Timer code:

Timer
{
    id: spawnTrigger

    interval: 1000
    running: true
    repeat: true
    triggeredOnStart: true

    onTriggered:
    {
        var randomX = Math.random() * 20 - 10;
        SceneManager.spawnCustomGeometry(sceneRoot, Qt.vector3d(randomX, 0, 0));
    }

    //This works fine.
    //Component.onCompleted:
    //{
    //    var randomX = Math.random() * 20 - 10;
    //    SceneManager.spawnCustomGeometry(sceneRoot, Qt.vector3d(randomX, 0, 0));
    //}
}

The 'SceneManager.spawnCustomGeometry()' function uses the 'createObject()' function to instantiate the custom geometry described inside a QML file,
which is loaded via Qt.createComponent().

The behaviour I get is the following:

- Using Qt v5.6.1:
    - If the 'triggeredOnStart' property is set to false, the custom geometry does not show up and the application continues running.
    - If the 'triggeredOnStart' property is set to true, the custom geometry shows up just once and the application continues running.

- Using Qt v5.7.0:
    - If the 'triggeredOnStart' property is set to false, the custom geometry does not show up and the application crashes.
    - If the 'triggeredOnStart' property is set to true, the custom geometry shows up just once and the application crashes.

With Qt v5.7.0, in both cases the call stack is the following (so far it has been the same for every crash):

- Call stack on Windows 7 x64 OS with MinGW32:
    1  QMetaObject::inherits                            qmetaobject.cpp    339 0x8d12b1
    2  Qt3DRender::Render::Entity::sceneChangeEvent     entity.cpp         213 0x3bf9bdf9
    3  Qt3DCore::QBackendNodePrivate::sceneChangeEvent  qbackendnode.cpp   82  0x380cfa1b
    4  Qt3DCore::QChangeArbiter::distributeQueueChanges qchangearbiter.cpp 132 0x380c1f12
    5  Qt3DCore::QChangeArbiter::syncChanges            qchangearbiter.cpp 179 0x380c21c0
    6  Qt3DCore::QAspectManager::exec                   qaspectmanager.cpp 273 0x380c7e07
    7  Qt3DCore::QAspectThread::run                     qaspectthread.cpp  85  0x380c8772
    8  QThreadPrivate::start(void *) *4                 qthread_win.cpp    391 0x78b777
    9  msvcrt!_itow_s                                                          0x76541287
    10 msvcrt!_endthreadex                                                     0x76541328
    11 KERNEL32!BaseThreadInitThunk                                            0x7673337a
    12 ntdll!RtlInitializeExceptionChain                                       0x76ef92e2
    13 ntdll!RtlInitializeExceptionChain                                       0x76ef92b5
    14 ??

- Call stack on Ubuntu Linux 14.04 x64:
    1 QMetaObject::inherits(QMetaObject const *) const                                                             0x7ffff65a8045
    2 ??                                                                                                           0x7fffde2d0d77
    3 Qt3DCore::QChangeArbiter::distributeQueueChanges(std::vector<QSharedPointer<Qt3DCore::QSceneChange>> *)      0x7fffddb923d8
    4 Qt3DCore::QChangeArbiter::syncChanges()                                                                      0x7fffddb9255f
    5 Qt3DCore::QAspectManager::exec()                                                                             0x7fffddb9e6e6
    6 ??                                                                                                           0x7fffddb9fa92
    7 ??                                                                                                           0x7ffff63d95f9
    8 start_thread                                                                            pthread_create.c 312 0x7ffff54db184
    9 clone                                                                                   clone.S          111 0x7ffff5b4937d

By the log messages I put inside the 'SceneManager.spawnCustomGeometry()' function, I can tell for sure that the call to 'createObject()' is being performed every time the timer event is triggered (as expected).

>From the results I got, it seems to me that no custom geometry can be instantiated once the parent object creation has been fully completed.
Am I right or did I overlook something important?

I have attached the test applications source code to this message, in case anyone needs it.

Any help would be greatly appreciated!

Best regards,
Carlo


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