[Interest] Qt3D widget

[Florian Blume]

I actually succeeded in implementing a Qt3D widget.

It can be found here: https://github.com/florianblume/qt3d-widget.

Unfortunately, I had to use Qt3D's internal classes so it kind of feels
a bit unstable because it might break with certain Qt versions.
I would have liked to leave all processing loops to Qt3D internally but
now have to drive them myself, which also feels a bit not so nice.

Anyways, I hope some other people can make use of it, too!

Best,
Florian

On 02.09.20 12:01, Florian Blume wrote:
> Hey,
>
> thanks for your quick answer!
>
> I actually had the version you described first running. I obtained the
> rendered image using QRenderCapture and then displayed it on the quad.
>
> I also already had the second idea that you described but thought it
> should be possible to obtain the texture from Qt3D and use it in OpenGL
> that's why I hadn't
> investigated this any further.
>
> Unfortunately, it's pretty difficult to run the aspect engine manually.
> I tried to place a processFrame() call in paintGL() - and even placed a
> doRender() call to
> the AbstractRenderer of the QRenderAspectPrivate after it like this:
>
> d->m_aspectEngine->processFrame();
>
> glClearColor(1.0, 1.0, 1.0, 1.0);
> glDisable(GL_BLEND);
> glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
>
> Qt3DRender::QRenderAspectPrivate *dRenderAspect =
> static_cast<decltype(dRenderAspect)>
>                    
> (Qt3DRender::QRenderAspectPrivate::get(d->m_renderAspect));
> Qt3DRender::Render::AbstractRenderer *renderer = dRenderAspect->m_renderer;
> renderer->doRender(true);
>
> Without the doRender() call it gets stuck the second time processFrame()
> is called - in
> Qt3DRender::Render::VSyncFrameAdvanceService::waitForNextFrame() where it
> tries to acquire a semaphore (which apparently doesn't have any more
> work ready).
>
> With the doRender() call it gets stuck in a similar place - but in the
> first call to paintGL in Qt3DRender::Render::Renderer::isReadyToSubmit()
> where it again tries to
> acquire a semaphore.
>
> I also don't understand whether it's enough that QOpenGLWidget binds a
> framebuffer before calling paintGL, it looks like in Scene3DRenderer
> this is enough to make
> Qt3D draw to that framebuffer.
>
> As you can see there are a lot of open questions which are difficult to
> answer. Do you have any suggestions where/how to look for answers?
> Obviously in the code itself,
> which is also difficult.
>
> Any help is appreciated,
> Florian
>
>
> On 01.09.20 18:28, Mike Krus wrote:
>> Hi
>>
>> Qt 3D source code has an example of how to use render capture in the manual tests.
>>
>> However this is probably not the right way to do it as 1/ it would require another FBO on top of the one QOpenGLWidget uses already; 2/ it transfers the image to the CPU which is not needed here.
>>
>> Think the way to do it is to do something similar to what is done for Scene3D:
>> - setup Qt 3D engine to be in manual mode (rather than using the simulation loop)
>>   by calling QAspectEngine::setRunMode(QAspectEngine::Manual)
>> - use QOpenGLWidget and in the paintGL method call QAspectEngine::processFrame()
>>   to have Qt 3D draw
>>
>> There’s of course lots of other stuff to setup. Might need a dummy offscreen surface to handle sizing, handling of the context, and a fair amount more.
>>
>> Mike
>>
>>> On 1 Sep 2020, at 16:51, Florian Blume <florian.blume at tu-berlin.de> wrote:
>>>
>>> Hi,
>>>
>>> I'm trying to implement a Qt3D widget since createWindowContainer is not
>>> suitable for me (always draws the Qt3DWindow on top of everything).
>>> I've already asked a Stackverflow question
>>> (https://stackoverflow.com/questions/63686309/use-qt3d-offscreen-rendered-texture-in-opengl)
>>> because I ran into
>>> several issues trying to display an offscreen texture that I render to
>>> with Qt3D in a QOpenGLWidget (it simply doesn't display anything).
>>>
>>> Has anyone some other solution regarding a Qt3D widget?
>>>
>>> Best regards,
>>> Florian
>>> _______________________________________________
>>> Interest mailing list
>>> Interest at qt-project.org
>>> https://lists.qt-project.org/listinfo/interest
>> —
>> Mike Krus | mike.krus at kdab.com | Senior Software Engineer
>> KDAB (UK) Ltd., a KDAB Group company
>> Tel: UK Office +44 1625 809908   Mobile +44 7833 491941
>> KDAB - The Qt Experts, C++, OpenGL Experts
>>
>>
> _______________________________________________
> Interest mailing list
> Interest at qt-project.org
> https://lists.qt-project.org/listinfo/interest