QT6 on Ubuntu 22.04 strange widget behavior

[Josef Lintz]

I have an update, no solution yet, but an update.

A user on Reddit suggested to that I run the app with -style fusion and -platform xcb, there wasn't much change there. Then he suggested I use export QT_LOGGING_RULES=*.debug=true before running the app, I ran the app once with XDG_CURRENT_DESKTOP set, and once with unset XDG_CURRENT_DESKTOP.

Comparing the two files, I found the following
.qpa.theme: Attempting to create platform theme "gtk3" via QPlatformThemeFactory::createqt.core.library: "/home/vbboard1/Qt/6.5.1/gcc_64/plugins/platformthemes/libqgtk3.so" loaded libraryqt.qpa.theme.dbus: "" "/org/freedesktop/portal/desktop" "org.freedesktop.portal.Settings" "SettingChanged"qt.qpa.gtk: Color map populated from defaults.qt.qpa.gtk: GTK theme initialized: "Yaru" Qt::ColorScheme::Lightqt.qpa.theme: Successfully created platform theme "gtk3"

As I understand, "Yaru" is a type of theme used by KDE. Why is it being loaded here with Ubuntu on gnome. Is there any way I can disable it?

[JoeCFD]

@Josef-Lintz If you want to set them for your app only, you can do it in main()
with
qunsetenv("GNOME_DESKTOP_SESSION_ID");
qunsetenv( "XDG_CURRENT_DESKTOP" );
before QApplication app call. These settings will affect your app only.

[JoeCFD]

@Josef-Lintz https://wiki.archlinux.org/title/Xdg-utils

XDG_CURRENT_DESKTOP=ubuntu:GNOME because you installed gnome.
mine is LXQt. You may need to make your code working for different settings.

[Josef Lintz]

@JoeCFD Thanks for the suggestion. I actually came up with a similar way to run the programs. I simply prefixed the program name with . and created a bash file with the same name as the program and before launching the program I do:
unset GNOME_DESKTOP_SESSION_ID
unset XDG_CURRENT_DESKTOP

But this doesn't solve the underlying issue. Why is it that on my system (A fresh install, bare in mind) with QT installed using the online installer, I get 3 different conflicting "styles(?)", when in designer, when running, or when modifying window/focus.

Also, your approach and mine still has the same issue(s), I have to do this for a lot of programs we use, so it's not very feasible.
And, it's only recently I noticed this issue, when I do
unset GNOME_DESKTOP_SESSION_ID
unset XDG_CURRENT_DESKTOP
Some of the widgets still appear wrong, I asked a question about this a while back (This was for Ubuntu 16.04). It ended up being an environment variable not being set correctly.

So, even if doing
unset GNOME_DESKTOP_SESSION_ID
unset XDG_CURRENT_DESKTOP
seems to work, it doesn't fix the issue fully

[Josef Lintz]

@JoeCFD Longshot. But do you know any QT "dependent" XDG settings which could affect this issue?

[JoeCFD]

@Josef-Lintz Can you check this output?
echo $XDG_SESSION_TYPE

I do not think Qt should have any issue with the following setting.
XDG_CURRENT_DESKTOP=ubuntu:GNOME

[Josef Lintz]

@JoeCFD

@Josef-Lintz Can you check this output?
echo $XDG_SESSION_TYPE

echo $XDG_SESSION_TYPE returns "x11"

I do not think Qt should have any issue with the following setting.
XDG_CURRENT_DESKTOP=ubuntu:GNOME

I think I figured out something. If I set XDG_CURRENT_DESKTOP to anyhing, not just unset it, I get the same result as the 3rd image. So, it's possible that XDG_CURRENT_DESKTOP is set correctly, but the preview/designer is wrong?
Also, still doesn't explain why the style changes when I move/resize the window

[Axel Spoerl]

Hi @Josef-Lintz,
with Qt 6.5, a new version of Qt's GTK3 theme has been shipped, which generally improves GTK look and feel. I wrote it, so now you know whom to blame ;-)

Looking at your observations:

• When the widget containing the progress bar and the push button is moved or resized, it implicitly gets focus. I guess that's the reason why the colors change. They change from the Inactive to the Normal color group. That said, the new GTK3 styling probably makes a change visible, that had been invisible before.
  You can check that by obtaining the widgets' palette e.g. with const QPalette &palette = ui->pushButton->palette();and inspecting their colors.
  This, as an example returns the normal button color.
  qDebug() << palette.color(QPalette::Normal, QPalette::Button).name();
  (change Normalto Inactive to retrieve the initial colors)

• Furthermore, this patch landed in 6.5.2 yesterday. It is (under more) related to the Yaru style. In essence, the GTK button foreground was used for the WindowText, before it would fall back to other (more suitable) colors. That has worked nicely for some GTK themes, but was unfortunate for others. It affects only text color, but since you are working with Yaru, I found it worth mentioning.

Cheers
Axel

PS: Thanks to @Matthias-Rauter for prompting.

[Josef Lintz]

@Axel-Spoerl Thank you very much for the explanation.
So, it seems like a small bug(?) in how the styles are set-up. Ok, but it still begs the question as to why "normal" is different in the designer vs runtime? And is it something I can fix "locally" or do I need to wait for an update?

And one more thing, (kind of a silly question) I can't seem to update to QT 6.5.2, I tried the unified installer, and I only got listings up QT 6.5.1?
According to this, QT6.5.2 has not yet been "Realized", my bad

[Axel Spoerl]

@Josef-Lintz
Hi Josef,
I understand the add-on-question. The widget designer provides an abstraction level to design widget based applications. It can't anticipate, where the application actually runs. Could be Linux/KDE, Linux/Gnome, Windows, macOS, dark mode, light mode. It doesn't have the ambition to completely emulate the look and feel of the local machine.
Cheers
Axel

[Josef Lintz]

@Axel-Spoerl I truly appreciate that you're explaining what the issue is. But how can I fix it, is it even something "fixable" on my end, or do I need to wait for the next QT version?

[JonB]

@Josef-Lintz
What are you expecting to be "fixed"? @Axel-Spoerl explained that Designer preview will not be identical to runtime. If it's that things look a bit different that is not going to change.

[Josef Lintz]

@JonB Well, if the designer is meant to preview how the program should look like, and it looks completely different from the preview during runtime, then I think the designer isn't working correctly (Assuming you don't do anything weird to the layout during runtime). And there should at least be a way to configure the designer, to make it preview the actual design more correctly.

(Bit of nit-pick I don't think calling it "slightly different" is doing this justice. Most of the widgets look completely different as to how they look in "design-time")

If the styling is different between design-time and runtime, maybe I can live with it. But the fact that the styles completely change when the widgets lose focus, is somewhat problematic, I guess that's the main issue here

I apologize if my earlier remarks came off as rude, that wasn't my intention.

[Josef Lintz]

This post is deleted!

[JonB]

@Josef-Lintz
I only meant if it looks "somewhat" different. If it's, say, a completely wrong color that would indeed be bad. @Axel-Spoerl knows much more than I do about the specifics.

[Axel Spoerl]

@Josef-Lintz said in QT6 on Ubuntu 22.04 strange widget behavior:

if the designer is meant to preview how the program should look like

I can understand the point. However, it would make the widget designer way more complex. Where should the line be drawn? Should it emulate macOS look'n'feel on Linux? Gnome YaruDark on Windows in light mode?

But that's getting us off topic: If there's anything we can improve on the GTK theming shipped with Qt 6.5, I'd be grateful for any input. And, as @JonB said, if the widget designer shows something completely odd, just point it out.

[Josef Lintz]

@Axel-Spoerl

I can understand the point. However, it would make the widget designer way more complex. Where should the line be drawn? Should it emulate macOS look'n'feel on Linux? Gnome YaruDark on Windows in light mode?

I mean, why not though? Isn't the point of the designer to preview how your program is going to look like? Having a designer which produces different output while in "design-mode" vs runtime, kinda defeats the point of having a designer?
QT apps (as far as I saw) already support theming, even "cross-platrform" themes, I can have a "Windows-looking" QT app run on Ubuntu. So I don't see the problem with said "line". I guess by default the designer should look like the system-theme, unless specified otherwise by the user.
If it's an issue of complexity, since QT Widgets is less supported than QT Quick, I can understand.

But that's getting us off topic: If there's anything we can improve on the GTK theming shipped with Qt 6.5, I'd be grateful for any input. And, as @JonB said, if the widget designer shows something completely odd, just point it out.

This is interesting, am I the first person to encounter this "issue"? Has nobody on Ubuntu 22.04 encountered this problem before? When installing Ubuntu I chose the "Minimal installation" option, could it be that it skipped something that a "Full installation" uses?

[Josef Lintz]

And one more thing, I just want to make sure that everyone understands by what I mean when I say "It looks different"

This is design-time

This is runtime

This is runtime-unfocused

[JonB]

@Josef-Lintz
Just so we are clear:

• Are you saying there is something wrong/unacceptable between the design time and the runtime other than the change of color?
• If the only issue is the change to orange color at runtime when (the window is?) unfocussed, then I would agree that would be surprising. Unless something about the desktop manage or the theme intends a dramatic change of color when not focussed.

Caveat that I don't use Qt6 and don't know anything about @Axel-Spoerl's "GTK theming shipped with Qt 6.5", so if that's what it's about I'm out of my depth.

[Axel Spoerl]

@Josef-Lintz
Regarding application style:
As indicated by @JonB, the color change between inactive and active is not a bug, it is emulating GTK behavior.

If you absolutely don't like it, there is a tweak you can apply.

Step 1: Extract GTK settings with bare colors

• set the environment variable QT_GUI_GTK_JSON_SAVE to a filename in a writable directory
• set QT_GUI_GTK_JSON_HARDCODED to true
• start your application and shut it down again.

Step 2: Inspect and modify JSON file

• open the new JSON file with the JSON editor of your choice
• search for the Hex RGB colors that you dislike and replace them with your favorite color

Step 3: Import the file

• unset the environment variables from step 1
• ship the edited JSON file with your application
• set the environment variable QT_GUI_GTK_JSON to the location of the edited file

From that moment, your application will look the way you styled it. However, it will no longer react to GTK theme changes. It will continue to respect dark/light mode and react on dark/light changes during run time.

Regarding widget designer / platform or theme emulation :
Feel free to submit a suggestion in https://bugreports.qt.io
Please do call it a suggestion, because that's what it is. If you file it as a bug, it will be closed invalid. I don't want to turn you down, but I see little hope for it to be implemented.

Regarding your summary question "Have we not had any feedback from other GTK users?"
Yes we have. A lot of positive feedback. Two bugs reported and fixed. Both of them my bad.