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Most widgets obscured, covered up by black

  • (Sorry to be monopolising this forum.)
    This is a strange one. The application that I'm porting from Windows to Linux is basically working now (as long as it is invoked in a terminal). But all the input screens are displayed with a flood of black that covers up most (but strangely not all) of the field labels. The situation is best conveyed by screenshots - the two attached pics are for one of the input screens,
    with Linux
    0_1568776891830_CaptureLinux.png ,

    and with Windows:
    The screen widget (tab_run) has this location in Designer:
    MainWQindow (QMainWindow)
    ----centralWidget (QWidget)
    --------stackedWidget (QStackedWidget)
    ------------tabs (QTabWidget)
    ----------------tab_run (QWidget)

    (There is a misalignment issue with the field labels, but that is just a font size issue.)

  • Moderators

    @gibbogle this seems to me like a stylesheet issue. Do you use stylesheets and do you set the background-color for any of your widgets?

    I would guess no :)

  • Lifetime Qt Champion


    To add to @J-Hilk, what desktop environment are you using on Linux ? Does it have a dark theme ?
    Are you using the distribution provided Qt ?

  • @j-hilk
    I don't know anything about stylesheets, and don't (knowingly) use them.
    No, I don't set a background color for any widgets.

    Edit: I should mention that it is only on the tabs member screens that this problem occurs. The other widgets that are members of stackedWidget do not have this problem.

  • @sgaist
    Whatever desktop environment I'm using is that which comes with Ubuntu 18.04, by default. I just installed 18.04 a few days ago and have changed nothing. How do I find out about my desktop environment?
    The Qt distribution is that installed by:

  • @j-hilk
    I found some helpful suggestions, and did this in main.cpp:

    //specify a new font.
    QFont newFont("Helvetica", 10, QFont::Normal, false);
    //set font of application
    foreach (QWidget *widget, QApplication::allWidgets()) {

    and this has solved the black problem!
    The alignment and sizing of many widgets is a bit different from in Windows, and requires some adjustments, but that's a relatively trivial issue.

    The global setting of widget fonts like this is effective, but not ideal, since it overrides any wanted variations introduced in Design. I guess what I really want is to scale the widget fonts globally - is that possible?

  • Moderators


    Not necessarily how I would have done it, but hey it works 😉

    Don't forget to set the topic via topic tools to solved!
    Happy coding

  • @j-hilk
    Feel free to suggest a better way. Any suggestions about how to reduce the font size while preserving, for example, the distinction between bold (e.g. titles) and normal text?

  • Moderators

    well, take a look at the high dpi display page of the documentation

    Useful to read anyway.

    What you're looking for is probably QT_SCALE_FACTOR which effects all fonts, scaled.

    It's an environment variable an can be set inside your code

    qputenv("QT_SCALE_FACTOR", "1.5");

  • @j-hilk
    Excellent! Just what I wanted. Thanks a lot.
    Everything is working now, except that I can't trigger the execution within Qt Creator.

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