How do I make objects in Qt3D move?

[Lias]

I have followed this example http://doc.qt.io/qt-5/qt3d-basicshapes-cpp-example.html in order to create a main window containing a Qt3Dwindow with a sphere entity in it. I use QSphereMesh to render the shape and QTransform to position it.

Now I wold like to let a user re-position the sphere to a given coordinate by the click of a pushbutton. I tried to use signals and slots with the slot calling the same function I use to position the sphere in the first place:

this->m_sphereTransform->setTranslation(QVector3D(10.0f, 0.0f, 0.0f));

(where m_sphereTransform is a Qt3DCore::QTransform). The program crashes and I am totally lost on how to actually make my objects move.

[Neosw]

You approach is good.
Have you check if the m_sphereTransform is already defines ?

[Lias]

As far as I can tell m_sphereTransform is only defined once.
However, my newest attempt is to initialize the transform with variables in the translation vector:

Qt3DCore::QTransform *sphereTransform = new Qt3DCore::QTransform();
sphereTransform->setTranslation(QVector3D(m_x, m_y, m_z));

where m_x, m_y and m_z are members of a class defining a sphere entity (with mesh, material and transform components). The class contains functions to set m_x etc

void Sphere::setX(int x)
{
  m_x = x;
}

when printing out m_x through the debugger it shows it has been changed. But the sphere doesn't move.
I have tried doing the same thing in QML instead of c++ and the sphere moves without problems. I suspect the view isn't refreshed?
In C++ I use a Qt3Dwindow:

Qt3DExtras::Qt3DWindow *viewRoom = new Qt3DExtras::Qt3DWindow();

and in QML a 3DScene:

Scene3D {
            id: scene3d
            anchors.fill: parent
            anchors.margins: 10
            focus: true
            aspects: ["input", "logic"]
            cameraAspectRatioMode: Scene3D.AutomaticAspectRatio

            SphereEntity {id: mySphere}
        }

Is there a difference between how the two updates what is shown on the screen?

[kshegunov]

@Lias said in How do I make objects in Qt3D move?:

when printing out m_x through the debugger it shows it has been changed. But the sphere doesn't move.

And why should it. You're setting a variable that has nothing to do with the sphere's transformation.

sphereTransform->setTranslation(QVector3D(m_x, m_y, m_z));

This makes a vector from the current values of m_x, m_y, m_z by copying their values. All modifications to said members after that will not cause the sphere's transformation to change.

[Neosw]

Hi,

You should add a QEntity as a parent of you QTransform to have a good clean up at the destruction of the QEntity.

For updating you QTransform, made it member of the class and add a method like this:

void Sphere::updateTransform(){
    if(_sphereTransform != 0){ //prevent seq fault
     _sphereTransform->setTranslation(QVector3D(m_x, m_y, m_z));
   }
}

[Lias]

@Neosw Thanks for your help. I tried this by myself two days ago and it worked!