[Interest] Qt3D widget

[Mike Krus]

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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—
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


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