[Interest] Qt3D widget

[Florian Blume]

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
>> _______________________________________________
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>> Interest at qt-project.org
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> —
> 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
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>
>