[Interest] Sporadic rendering problem QtQuick/OpenGl

[Gunnar Sletta]

Hi Patrick,

The bug is not known to me, but it looks like there is a bug with the geometry being passed to OpenGL by the rendering code. A hint that may help you track down the root of the problem could be too specify the environment variable QSG_RENDERER_DEBUG=upload and look at the vertexdata. There'll be a lot of output there, but it might help to provide some pointer as to where the problem lies. 

If you manage to make a testcase that consistently reproduces it, please file the bug to bugreports.qt.io.

cheers,
Gunnar


> On 19 Oct 2016, at 23:22, Patrick.Flaig at continental-corporation.com wrote:
> 
> Hi,
> I got the recommodation to send my question/problem to this mailing list.
> 
> On our i.MX6 based target device we can observe sporadic rendering problems when using QtQuick.
> As the problem is only happening sporadic we were not able to create a specific code that is causing the rendering problem.
> 
> Background information: our system has two framebuffers, Qt is rendering in the foreground framebuffer.
> We are using Qt 5.6 running on a Linux Kernel 3.10.17 (patches from NXP for the iMX6 are applied), including latest opengl libraries from NXP.
> 
> We have seen two issues: 
> 1.        Triangle showing parts of the background framebuffer.
> 
> 2.        Warped Graphics
> 
> We have already started a discussion with NXP regarding that issue.
> The last statement from NXP is: 
> 1.        Eventually I suspect here an error in the QT framework when passing the mesh to OpenGL. It can be that for example a very simple geometry is used in the vertex buffer (e.g. 2 triangles defining the full frame buffer) but in the end 3 or more triangles are specified due to an application software error, so the OpenGL pipeline tries to render a 3rd triangle. For that it reads the coordinates from the vertex buffer (that contains valid data only for 2 triangles !), and thus invalid data is read therefore random triangles appear on the screen. 
> 2.        In this example again it looks like a geometry problem. Because the texture containing the gauge appears to be mapped on a strange 2d mesh composed by two incomplete circles. My idea with alpha was just to confirm that some draw primitives are corrupted, which is pretty clear now.
> 
> Does anybody know about existing Qt bugs which could cause the issue we can observe?
> Any ideas how to debug this issue?
> 
> Thanks a lot.
> 
> Patrick 
> 
> http://www.continental-corporation.com
> 
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