How to register kvantum (without using qt5ct) in QT_QPA_PLATFORMTHEME?

[unihorn78]

Subj

How to register kvantum (without using qt5ct) in QT_QPA_PLATFORMTHEME?

export QT_QPA_PLATFORMTHEME=kvantum (Kvantum, kvantum-style, etc) does not work.

[tsujan]

QT_QPA_PLATFORMTHEME is about the Qt platform theme (plugin), while Kvantum is a style plugin and is about QT_STYLE_OVERRIDE. The second variable requires the first to be set. The first one needs a "Qt platform-theme plugin".

Qt DEs (KDE, LXQt) automatically activate their own platform-theme plugins; the user just chooses the style (Kvantum, for example) and one of its themes.

Under non-Qt DEs, qt5ct, QGnomePlatform, or lxqt-qtplugin,... can be used. All of them are about the variable QT_QPA_PLATFORMTHEME that you mentioned.

[tsujan]

An example:

Under Enlightenment, I set QT_QPA_PLATFORMTHEME to lxqt and QT_STYLE_OVERRIDE to kvantum (with small letters). Of course, I have installed lxqt-qtplugin (and its config) for the first variable.

[unihorn78]

Thank you so much.

I made "export QT_STYLE_OVERRIDE=kvantum"

And it all worked.

[tsujan]

You're welcome.

So, on your system, QT_QPA_PLATFORMTHEME was already exported in a proper way.

[spikespaz]

Sorry to necro this thread but... I would like to know if anyone is aware of what component of KDE handles the theming. I find that all of the options presented look very bad with some Qt programs, and I never noticed a single issue on KDE. If I can rip that out to replace qt5ct, you would be my hero.

[tsujan]

what component of KDE handles the theming

Its Qt plugins, namely, its platform-theme plugin (/usr/lib/qt/plugins/platformthemes/KDEPlasmaPlatformTheme.so) and its icon engine plugin (/usr/lib/qt/plugins/iconengines/KIconEnginePlugin.so). The first one allows style changing, the second one handles icons, both through KDE's System Settings . You can't "rip them out".

But if you have a full KDE installation, you might be able to use this command outside KDE to run APP:

export XDG_CURRENT_DESKTOP=KDE && APP

Similarly, if you have a full LXQt installation, you could use this command outside LXQt:

export XDG_CURRENT_DESKTOP=LXQt && APP

[spikespaz]

If I wanted the fewest packages from either desktop environment possible, what route would you take? Can I just install KDE settings and get those two plugins, or get the packages that work together without the entire plasma desktop metapackage?

[tsujan]

Can I just install KDE settings and get those two plugins

Probably, those plus kiconthemes, but they depend on a lot of other packages.

However, it's unusual to install so many packages just for use outside KDE. That's why qt5ct has been made. It has its own independent platform-theme plugin.