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Random white squares in my window



  • In Qt5.11 I have a problem with white squares (8x8) appearing in my QML application. Usually it happens, where text rendered.
    If a text with this problem changes (just changing the color is enough), the squares disappear. When changing the text back, the problem is back.
    If I have multiple widgets with the same text, sometimes both of them have the squares on identical positions in the text.
    When restarting the application, the squares may disappear or be in different positions.
    Rarely I see the squares where an image is displayed.
    The size of the sqares always seems to be 8x8 pixels.
    It's not a displaying / video problem. If I make a screenshot using QQuickWindow::grabWindow(), it's in the image, too.
    In the appended image, the numbers 1 and 0 have the problem.
    screenshot-part.png

    Is there any idea, what I can try to fix this?

    Thanks!


  • Lifetime Qt Champion

    Hi and welcome to the forums
    What platform are you on ?
    Did you check that your OpenGL is ok using some other app?
    Do you also see these white dots if you run tsome of the QML examples ?
    Did you try app on other device to see if that also gets white dots ?`



  • Hello mrjj,
    thank you for your reply.

    The application runs on Wayland (Weston with drm backend) on an ARM machine.
    On other devices (older Qt versions, eglfs@ARM) or X@x86-64) there are no problems.
    Non-Qt applications (also with 3d acceleration) work fine.

    I will test the QML examples.



  • I did some more testing, but still nothing helped.

    • Sometimes, the same letters have the exact same problem. Could there be some graphics buffer problem?
    • Sometimes there are not white squares, but black/white patterns
    • It happens with different screen resolutions on different devices (of the same type)

    So far I have not seen the effect with qteverywhere-demo or other qt examples.

    I ran profilers and static analyzers to check for memory problems, but nothing relevant was found in our code.

    Are there any ideas?

    screenshot2.png


  • Lifetime Qt Champion

    Hi
    It really looks like a driver issue but since you never it with Qt QML samples, its a bit odd.
    It could be related to the actual font but if you see this on different system its hard to imagine they all have a broken font file unless all came from same image/clone ?



  • Hello mrjj,
    After updating Qt, I was able to see the same problem in the qt demos, too.
    As you assumed, it is a graphics driver bug The processor manufacturer confirmed and fixed the issue.
    Thank you for your help!


  • Lifetime Qt Champion

    @Cubi
    Im glad to hear you found the reason and thank you for reporting back.


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