[Interest] Build a Qt3D scene in C++ and use it in a QtQuick one

[dns.botond at gmail.com]

Yes, that would work altough I would have preferred a way which doesn't
require the C++ entity hierarchy to be exposed to the QML code, just to
be assigned back to a property on the Scene3D object. In any case I can
use it like this for now until I find a better solution.
Since parts of the Qt3D API is still WIP I'm hoping that such a better
solution will be provided.

On Thu, 2018-09-06 at 18:49 +0000, Gil H wrote:
> If all you need is to have Scene3D as part of your QML but the entire
> entity hierarchy come from C++, then you should be able to do that
> just by creating the C++ entities and passing the root to the entity
> property of the Scene3D item. You can set properties on QML items
> from C++ and you can read values from C++ inside your QML. Many 3D
> entities are easier to describe in QML (e.g. the framegraph itself
> and custom materials), and I'm not sure of the implications of mixing
> entities created in C++ and QML in terms of object ownership,
> threading, lifecycle, etc. I've slogged through so many crashes and
> freezes when trying to adopt Qt3D in an “unconventional” use case
> that I can't remember each issue I've faced along the way. But
> hopefully things will go more smoothly for you. Highly recommend
> basing any work off the very latest Qt3D code if you can (5.11.2
> branch)
> 
> Cheers,
> 
> Gil
> 
> On 9/6/18, 2:36 PM, “interest-bounces+qt=tastytech.ca at qt-project.org
>  on behalf of dns.botond at gmail.com” <
> interest-bounces+qt=tastytech.ca at qt-project.org on behalf of 
> dns.botond at gmail.com> wrote:
> 
> Hi,
> 
> According to the documentation [1] there are two ways to use Qt3D:
> * From C++.
> * From QML.
> 
> There is also a bridge class (Qt3DScene2D) which allows rendering a
> QtQuick2 content into a Qt3D scene and another one (QtQuick.Scene3D)
> which allows for the opposite, rendering a Qt3D scene into a QtQuick
> one, however this latter only allows working with the Qt3D QML types.
> What I would like to do is to generate the scene from C++ and use it
> in
> a QtQuick2 GUI. Kinda like how inheriting from QQuickItem allows one
> to
> do the drawing in C++ and seamlessly integrate the resulting item
> into
> a QML scene.
> Looking at the sources [2] this should be easily achievable, all we'd
> need is a slightly modified `Scene3DItem` class which allows the
> inheriting class to set up the entity tree and other aspects of the
> scene and not allowing these to be meddled with from QML (basically
> stripping all existing properties and invokables and requiring them
> to
> be set by C++ code).
> 
> Are there any plans to allow for something like this? Or is there
> already a way to do this that I'm not aware of?
> 
> Regards,
> Botond
> 
> [1] https://doc.qt.io/qt-5/qt3d-index.html
> [2]
> https://code.qt.io/cgit/qt/qt3d.git/tree/src/quick3d/imports/scene3d
> 
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