Most widgets obscured, covered up by black

gibbogle

(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
,

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.)

J.Hilk

@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 :)

SGaist

Hi,

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 ?

gibbogle

@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.

gibbogle

@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:
qt-opensource-linux-x64-5.13.0.run

gibbogle

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

mainWin.showMaximized();
//specify a new font.
QFont newFont("Helvetica", 10, QFont::Normal, false);
//set font of application
QApplication::setFont(newFont);
foreach (QWidget *widget, QApplication::allWidgets()) {
    widget->setFont(QApplication::font());
    widget->setStyleSheet("background-color:white;");
    widget->update();
}

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?

J.Hilk

@gibbogle

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

gibbogle

@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?

J.Hilk

@gibbogle
well, take a look at the high dpi display page of the documentation
https://doc.qt.io/qt-5/highdpi.html

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");

gibbogle

@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.

Go Fish

@gibbogle I should noe that setting font using setFont() on a widget with QSS not guaranteed to work (it shouldn't work but in someversions and patforms it does). These are related to two different ways to render windet.
A call to

widget->setAutoFillBackground(true);

should have same result here. Upscaling and other visual effects require autofiling or background will be black. QSS use equals to activating autofill.