A weird bug? Why is there no spatial depth in my 3D scene?

  • @kshegunov I can really exclude this. I reproduced this very often before I made the efforts to post this. Also now I am reproducing it. Furthermore, if I rotate the orbit view by ~180° around the z-axis manually with the mouse, it still does not change the fact that the lastly instantiated sphere is still in front. Therefore, it is not possible that I am just confusing the sphere positions here. While doing the rotation around the z-axis, the smallGreenSphere changes its size as it should do because it is not in the ViewCenter but, as already said, the spatial depth is wrong. The lastly created QEntity is always in the foreground and the other objects are behind it.
    Of course, I experience this also with the ball-and-stick molecules which I originally want to visualize. This applies also to QCylinders and whatsoever.

    Maybe I found a weird bug here?

  • Hi,
    I cannot reproduce this problem, either.
    I remember, though, I had similar issues using QPhongAlphaMaterial when I tested Qt3D. For the time being(?), we stay with QOpenGLWindow, as it has no known bugs and most important to us produces no 13% CPU load (in release version) with just two cubes to show.

  • Qt Champions 2017

    @Finn said in A weird bug? Why is there no spatial depth in my 3D scene?:

    Maybe I found a weird bug here?

    It is possible.You can take a peek here to see if something's known.
    What's your OS and how did you install Qt3D?

  • @kshegunov My OS is ubuntu 16.04 LTS and I got Qt 5.7 via the qt-unified-x64-2.03-1-online.run executable. In the terminal, I went into my Qt directory
    /home/<username>/Qt/5.7/Src where I just entered

    sudo make install

    When wanted to compile a Qt3D example, I got some linking errors saying something about missing Qt3D libraries (which I cannot recall anymore). I could solve this by entering the following which I found in some forum:

    sudo apt-get install libfontconfig1-dev libfreetype6-dev libx11-dev libxext-dev libxfixes-dev libxi-dev libxrender-dev libxcb1-dev libx11-xcb-dev libxcb-glx0-dev libxcb-keysyms1-dev libxcb-image0-dev libxcb-shm0-dev libxcb-icccm4-dev libxcb-sync0-dev libxcb-xfixes0-dev libxcb-shape0-dev libxcb-randr0-dev libxcb-render-util0-dev libxcb-xinerama0-de

    Maybe this is the origin of my problems?
    Should I consider reinstalling Qt completely and what would be the cleanest way to do it? Thanks a lot for your help.

  • Qt Champions 2017

    @Finn said in A weird bug? Why is there no spatial depth in my 3D scene?:

    Maybe this is the origin of my problems?

    It's certainly possble.

    sudo make install

    Why do that? Your distro already provides a Qt release so my suspicion is there are some files (partially) overwritten. What I suggest is to reinstall you distro's Qt (by means of the package manager), then to configure the Qt you downloaded with a prefix (don't forget to make clean before doing the configure, or even to delete the whole folder and recreate it through the Qt installer), e.g.:

    ./configure -prefix /opt/Qt-5.7

    make and then it's safe to make install, because the files will go to /opt/Qt-5.7.
    Then you can configure a kit in creator (assuming this is what you use) that will use this version of Qt (in /opt/Qt-5.7).

  • @kshegunov No, I completely reinstalled everything to the folder /opt/Qt-5.7 by following your instructions and those in the tutorial (https://wiki.qt.io/Install_Qt_5_on_Ubuntu). Before, I deleted everything but the result is the same. So far I used CLion2016 and now I also tried the QtCreator - still the same outcome.

    I also added some axes (x=red, y=green, z=blue), which are instantiated after the spheres.

    view 1
    view 2

    Other ideas?


    #include <QGuiApplication>
    #include <Qt3DCore>
    #include <Qt3DRender>
    #include <Qt3DExtras>
    Qt3DCore::QEntity* createTestScene() {
      Qt3DCore::QEntity* root = new Qt3DCore::QEntity;
      Qt3DCore::QEntity* smallGreenSphere = new Qt3DCore::QEntity(root);
      Qt3DCore::QEntity* bigRedSphere = new Qt3DCore::QEntity(root);
      Qt3DExtras::QSphereMesh* bigMesh = new Qt3DExtras::QSphereMesh;
      Qt3DExtras::QSphereMesh* smallMesh = new Qt3DExtras::QSphereMesh;
      Qt3DExtras::QPhongMaterial* redMaterial = new Qt3DExtras::QPhongMaterial;
      Qt3DExtras::QPhongMaterial* greenMaterial = new Qt3DExtras::QPhongMaterial;
      Qt3DCore::QTransform* transform =  new Qt3DCore::QTransform;
      Qt3DCore::QEntity* xaxis = new Qt3DCore::QEntity(root);
      Qt3DCore::QEntity* yaxis = new Qt3DCore::QEntity(root);
      Qt3DCore::QEntity* zaxis = new Qt3DCore::QEntity(root);
      Qt3DExtras::QCylinderMesh* cylinderMesh = new Qt3DExtras::QCylinderMesh;
      Qt3DExtras::QPhongMaterial* blueMaterial = new Qt3DExtras::QPhongMaterial;
      double pi = 3.14159265359;
      Qt3DCore::QTransform* xTransform = new Qt3DCore::QTransform();
      Qt3DCore::QTransform* yTransform = new Qt3DCore::QTransform();
      Qt3DCore::QTransform* zTransform = new Qt3DCore::QTransform();
      return root;
    int main(int argc, char* argv[]) {
      QGuiApplication app(argc, argv);
      Qt3DExtras::Qt3DWindow view;
      Qt3DCore::QEntity* scene = createTestScene();
      // camera
      Qt3DRender::QCamera *camera = view.camera();
      camera->lens()->setPerspectiveProjection(45, 16./9., 0.1,1000.);
      camera->setViewCenter(QVector3D(0, 0, 0));
      // manipulator
      Qt3DExtras::QOrbitCameraController* manipulator = new Qt3DExtras::QOrbitCameraController(scene);
      return app.exec();


    cmake_minimum_required(VERSION 3.2)
    find_package(Qt5 REQUIRED COMPONENTS
    add_executable("${PROJECT_NAME}_main" main.cpp)

  • Qt Champions 2017

    This is really strange. I ran your code and it works perfectly fine for me (I use qmake with a kit for Qt 5.7 though). Here's what I see:

    And my project file is absolutely standard:

    QT       += core gui 3dcore 3drender 3dextras
    TARGET = balls-test
    TEMPLATE = app
    SOURCES += main.cpp

    [Edit: Fixed broken link]

  • @kshegunov I tried using qmake for building but again the same outcome.

  • Qt Champions 2017

    Honestly, I'd be surprised if there was a difference between using cmake and qmake. And to be completely frank I don't know what might be the cause of the problem. My current best advice is to either bring the question to the mailing list, where hopefully one of the developers of Qt3D will pick it up (but after you check there's no open bugs on this), or try and wait for some other suggestion from other of our members here.

    Kind regards.

  • I tried it on my private MacBook Pro with MacOS Sierra 10.12.1 and installed Qt5 via brew install qt5. The result is still the same. What on earth can be the reason that it is working for you guys and not for me? Do I need some other libraries or build options?

  • Sorry, as a noobie, I can't offer any insight, but I ran the code, and I'm getting the same as Finn. I'm on Qt 5.7 on Win 10.

    alt text

    Could it be CPU or GPU related? I'm on a 6coreAMD machine.

  • @Ian-Bray Thank you for your reply, this was very helpful! I would suggest that someone more experienced than me should report this as a bug.

  • Qt Champions 2017

    @Finn said in A weird bug? Why is there no spatial depth in my 3D scene?:

    this was very helpfu

    Indeed, it was.

    I would suggest that someone more experienced than me should report this as a bug.

    There's nothing to it, you just describe the problem and attach the screenshots and the code from upstairs as a minimal reproducible example (preferably with a simple project file). As for the problem itself it may be helpful if we can squeeze some more information out. I may be running a newer (or older) version of Qt compared to you. Can you both state the full version (with patch number). I'm running Qt 5.7.2 built from git some time ago on a Linux 4.8.11 kernel.

  • @kshegunov

    I'm using qt-opensource-windows-x86-mingw530-5.7.0 on Win 10, if I get a chance I'll try it on Linux later.

  • Sorry, this isn't going to be helpful. Just to report that both slabs of code crashed on Qt 5.7.1 GCC 64 on latest Mint.
    Possibly due to lack of RAM. Not sure.

  • @Ian-Bray With Qt 5.7.1 the example works now perfectly fine for me.

  • Qt Champions 2017

    Then probably it's a bug that was fixed with the patch version in the meantime. Cheers!

  • @Finn Thanks Finn. I'll update later!

  • @kshegunov Must have been quite a big one. I ran the 3d Materials Example on 5.7.0 two days ago - it was horrible. I updated to 5.7.1 yesterday and ran it again - works perfect now.

  • Qt Champions 2017

    Well, 5.7.0 was Qt3D's first official release, and the code hasn't matured as much as the other modules, so some bumps along the road are expected. My biggest beef with Qt3D actually is its very thin documentation, but I'm sure that'll improve with time.:)

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