How can I make my app ignore window's "HIGH DPI SCALING"?

Curtwagner1984

Greetings,

My app's UI goes crazy when I move it to a screen that has a high DPI scaling enabled(150%) instead of (100%).

This is probably a sign of a bad widget design, but that's a problem for another day. For now, I just want my app to ignore the HIGH DPI SCALING option in windows if it's possible.

I looked at this answer but I've put AA_DisableHighDpiScaling instead of AA_EnableHighDpiScaling in my main.cpp:

    QApplication a(argc, argv);

    QApplication::setAttribute(Qt::AA_DisableHighDpiScaling); // Disable DPI support

But it has no effect. When I set the scaling to be 100% on the other screen everything is fine.

I would appreciate it if someone knows how to make my app ignore said scaling.

Thank You!

J.Hilk

@Curtwagner1984 reading through the documentation of AA_DisableHighDpiScaling

Disables high-DPI scaling in Qt, exposing window system coordinates. Note that the window system may do its own scaling, so this does not guarantee that QPaintDevice::devicePixelRatio() will be equal to 1. In addition, scale factors set by QT_SCALE_FACTOR will not be affected. This corresponds to setting the QT_AUTO_SCREEN_SCALE_FACTOR environment variable to 0. This attribute must be set before QGuiApplication is constructed. This value was added in Qt 5.6.

it clearly states, that attribute has to be set before the creation of the QApplication, you seem to do it afterwards.

Curtwagner1984

Thank you! For some reason I assumed this needs to be done after.

It's like this now:

    QApplication::setAttribute(Qt::AA_DisableHighDpiScaling); // Disable DPI support

    QApplication a(argc, argv);


    MainWindow w;
    w.showMaximized();
    
    return a.exec();

But it doesn't really seem to have an effect.

This is how it looks on a display with 100% scaling 100 scaling and this is how it looks on a display with 150% scaling 150 scaling

JKSH

@Curtwagner1984 said in How can I make my app ignore window's "HIGH DPI SCALING"?:

it doesn't really seem to have an effect.

Try running your app in "DPI Unaware" mode: https://doc.qt.io/qt-5/highdpi.html#migrate-existing-applications

Curtwagner1984

Thanks,
I made a file named qt.conf with the line

<application> -platform windows:dpiawareness=0

And put it in the the folder of the executable. Nothing changed.

Is this correct? Should application be the name of the application?

JKSH

@Curtwagner1984 said in How can I make my app ignore window's "HIGH DPI SCALING"?:

I made a file named qt.conf with the line
<application> -platform windows:dpiawareness=0

Those are command line arguments. You pass the extra arguments while launching your .exe from the Command Prompt .

Curtwagner1984

Thank you! This works!
Is there a way to set it up in the application itself, without the need to provide extra command line arguments?

J.Hilk

@Curtwagner1984
good old putenv, probably

https://www.cprogramming.com/fod/putenv.html

JonB

@J-Hilk
I looked at this. What environment variable name (and value) are you proposing for -platform windows:dpiawareness=0, I could not see that it worked this way??

J.Hilk

@JonB admittedly
the official way to do it, is apparently the creation and deployment of a qt.conf file, same level as the executable with this content:

[Platforms]
WindowsArguments = dpiawareness=0

that said:

qputenv("dpiawareness", "0"); or qputenv("windows:dpiawareness", "0");

I'm unsure, I'm not using it often enough :D

JonB

@J-Hilk said in How can I make my app ignore window's "HIGH DPI SCALING"?:

qputenv("dpiawareness", "0"); or qputenv("windows:dpiawareness", "0");
I'm unsure, I'm not using it often enough :D

There is/I can see no evidence that a Qt program would recognise either of these proposed environment variable names. Unless you can see where it says it does.... I see only the command line or qt.conf file approaches so far.

Curtwagner1984

@J-Hilk said in How can I make my app ignore window's "HIGH DPI SCALING"?:

[Platforms]
WindowsArguments = dpiawareness=0

Thank you! I tried to used this before but I've put incorrect syntax in this file. This works.

arunkannan

@Curtwagner1984 @JonB @J-Hilk @JKSH
I used Python PyQt5-5.15 for my application
I have guimain.exe and panelgui.ui files . Made qt.conf file
But when I change windows scaling to 125% or 150% the text fonts and other ui widgets get messed up...how to make it work i.e disable windows scaling for application

Violet Giraffe

In Qt 6 you can override the scale factor with the QT_SCALE_FACTOR env variable, but there is a problem: it doesn't set the factor to your value, it multiplies it. For example, if the system has 150% and you want 100%, you need to set QT_SCALE_FACTOR to 0.666667 (and even then it might not end up exactly 1.0 but rather 1.0001).

Is this intentional? There is a number of problems resulting from this multiplicative behavior, the primary one being when the application is moved between screens with different scale factors. I want to have 1.0 everywhere, not 0.66!

Also, -platform windows:dpiawareness=0 DOES NOT WORK!
Or, rather, it does the wrong thing. It disables too much, devicePixelRatio() reports 1.0 but the window is stretched and blurry.

Violet Giraffe

Found the proper option: QT_ENABLE_HIGHDPI_SCALING=0.