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Sporadic rendering problem QtQuick/OpenGl

  • Hi,

    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?

    [Moved to QML and Qt Quick ~kshegunov]

  • Qt Champions 2017

    @_patrick_ said in Sporadic rendering problem QtQuick/OpenGl:

    Does anybody know about existing Qt bugs which could cause the issue we can observe?

    I don't, but the bugtracker is publicly accessible, you can check it here. Also note that the forum has problems with uploaded files, so you should rather upload your images to an external site and reference them here. You can use ![](image url) to insert an inline image.

  • Added the pictures.
    Someone any idea?

  • Lifetime Qt Champion


    If the bug tracker did return anything then I'd recommend posting this question to the interest mailing list. You'll find there Qt's developers/maintainers. This forum is more user oriented.

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