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Qt3D (C++) 2D Text (overlay) on top of Qt3DWindow

  • Hi,

    First I'm new to the Qt3D framework.
    I'm trying to put 2D text on top of a Qt3DWindow or the widget created from it. I tried multiple unsuccessful approaches and hope you can give me some clues as there is very few information and forum posts about that.

    For now I've tried to:

    • Use the QText2DEntity class. But it's actually creating a text in 3D space, which I don't want, I want a simple text on top of the 3D view.
    • Create a QLabel and raising it above the QWidget (using the raise() method) returned from the createWindowContainer(my3DWindow).
    • Using the paintEvent and QPainter.

    Now a thing that I didn't tried would be to create another viewport with an orthographic camera, and rendering a QText2DEntity. Is this a proper way to do that using this framework ? If so could you give me some pointers on which classes I should take a look at ?

    I would rather prefer to be able to draw widgets on top as I could use other components (ie: sliders, buttons).

    Thank you in advance !

  • Moderators

    Your best bet is to use what comes from the Qt3D module. Other options are to embed a QML view inside the widget and use its elements to overlay over the window. The problem is that the Qt3D engine brings up a scene graph tree that is going to repaint the window, if you try to overlay something widget over it. It's a syncing issue, which ain't trivial to solve. On the other hand if you stick to QML, Qt3D integrates into the QML scene graph and it works properly. So in conclusion I suggest you use QML for that purpose, or stick with Qt3D's 2D primitives.

  • Okay thanks for the insights unfortunately I'm not very familiar with QML. Can you elaborate more on what Qt3D's 2D primitives are?

  • Moderators

    That'd be QMesh with a properly oriented quad (i.e. QPlaneMesh) + a texture and QText2DEntity. I don't believe there's much else.

    PS. Another thing that came to mind is to use native widgets for the overlay, but that can be really costly if there are many.

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