[Interest] [External] Re: Qt3D Fit in view

Sean Murphy Sean.M.Murphy at us.kbr.com
Fri Mar 10 13:45:30 CET 2023

> > Issue 1: QEntity::setEnabled(false) doesn't seem to make the entity
> > invisible  Each radio button is connected to a corresponding slot which
> > just does the following:
> >
> >    void MainWindow::slotEntity1Toggled(bool checked)
> >    {
> >      qDebug() << __FUNCTION__ << checked;
> >      Entity1 ->setEnabled(checked);
> >    }
> >
> Please provide more details on how the view is setup.

Sure. Here's the code that sets up the view & scene

  view = new Qt3DExtras::Qt3DWindow();
  Qt3DCore::QEntity *scene = createScene();  // <- explained below
  Qt3DRender::QCamera *camera = view->camera();
  camera->lens()->setPerspectiveProjection(45.0f, 16.0f/9.0f, 0.1f, 100000.0f);
  camera->setPosition(QVector3D(0, 0, 750));
  camera->setViewCenter(QVector3D(0, 0, 0));
  Qt3DExtras::QOrbitCameraController *camController = new Qt3DExtras::QOrbitCameraController(scene);
  camController->setLinearSpeed( 1000.0f );
  camController->setLookSpeed( 180.0f );

  QWidget* w = QWidget::createWindowContainer(view, this);
  // from here I add the widget "w" to my main window

The createScene() function does the following:
  // Root entity
  Qt3DCore::QEntity *rootEntity = new Qt3DCore::QEntity;

  // Material
  Qt3DRender::QMaterial *material;

  // Entity
  mEntity = new Qt3DCore::QEntity(rootEntity);
  Qt3DRender::QMesh *mMesh = new Qt3DRender::QMesh(rootEntity);
  material = new Qt3DExtras::QPhongMaterial(rootEntity);

> > Issue 2: Is there any sort of "fit in view" functionality for 3D views?
> >
> >  Since I'm only allowing the user to display one entity at a time, I'd
> > like to be  able to automatically set the camera settings to zoom as
> > needed to fit the entire  entity within the view, so the user doesn't
> > have to manually zoom in/out as they  switch between entities.
> >
> >  The .obj files I'm playing around with have VASTLY different scale
> > factors so a  camera setting for one entity often doesn't work well for
> > another.
>  There's relevant methods on the QCamera class.

Shortly after posting my original message, I did stumble across
QCamera::viewEntity() and added that. So now in my slot that is supposed
to enable/disable an entity I do the following:

  void MainWindow::slotEntity1Toggled(bool checked)
    qDebug() << __FUNCTION__ << checked;
    if(checked  && view && view->camera())

This change ALMOST works, like the first issue, after I make this call,
the new entity is shown, but the old entity is still visible too, and the
camera is still at the same position as before. I have to do something that
forces the view to resize before the camera actually changes position and
the scene gets rendered correctly. As soon as that resize happens, the
scene is re-rendered exactly as I want: the previous entity is no longer
visible, the new entity is centered and fits nicely within the view.

So I'm getting closer - I just seem to be missing something that triggers
the scene to get rendered again after I make changes - basically whatever
the Qt 3D equivalent of QWidget::repaint() is. I haven't stumbled across
that yet.


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