[Interest] Qt3D widget

Mike Krus mike.krus at kdab.com
Tue Sep 1 18:28:57 CEST 2020


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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