XnView 1.8.6 does not honor system font settings on KDE Plasma 6

bvitnik · Post by **bvitnik** » Sat Mar 29, 2025 8:59 pm

Hi.

After upgrading KDE from 5.x to 6.3, XnView MP is using wrong font and font size for UI. My understanding is that this comes from XnView being based on Qt 5 and using it's own distribution of Qt 5 vs KDE using Qt 6. If I run XnView with:

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QT_DEBUG_PLUGINS=1 xnview

I get some insight into the problem:

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QFactoryLoader::QFactoryLoader() checking directory path "/opt/XnView/lib/platformthemes" ...
QFactoryLoader::QFactoryLoader() looking at "/opt/XnView/lib/platformthemes/libqgtk2.so"
Found metadata in lib /opt/XnView/lib/platformthemes/libqgtk2.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformThemeFactoryInterface.5.1",
    "MetaData": {
        "Keys": [
            "gtk2"
        ]
    },
    "archreq": 0,
    "className": "QGtk2ThemePlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("gtk2")
QFactoryLoader::QFactoryLoader() looking at "/opt/XnView/lib/platformthemes/libqgtk3.so"
Found metadata in lib /opt/XnView/lib/platformthemes/libqgtk3.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformThemeFactoryInterface.5.1",
    "MetaData": {
        "Keys": [
            "gtk3"
        ]
    },
    "archreq": 0,
    "className": "QGtk3ThemePlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("gtk3")
QFactoryLoader::QFactoryLoader() looking at "/opt/XnView/lib/platformthemes/libqt5ct.so"
Found metadata in lib /opt/XnView/lib/platformthemes/libqt5ct.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformThemeFactoryInterface.5.1",
    "MetaData": {
        "Keys": [
            "qt5ct"
        ]
    },
    "archreq": 0,
    "className": "Qt5CTPlatformThemePlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("qt5ct")
QFactoryLoader::QFactoryLoader() looking at "/opt/XnView/lib/platformthemes/libqxdgdesktopportal.so"
Found metadata in lib /opt/XnView/lib/platformthemes/libqxdgdesktopportal.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformThemeFactoryInterface.5.1",
    "MetaData": {
        "Keys": [
            "xdgdesktopportal",
            "flatpak",
            "snap"
        ]
    },
    "archreq": 0,
    "className": "QXdgDesktopPortalThemePlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("xdgdesktopportal", "flatpak", "snap")
QFactoryLoader::QFactoryLoader() checking directory path "/opt/XnView/platformthemes" ...
QFont::fromString: Invalid description 'Noto Sans,8,-1,5,400,0,0,0,0,0,0,0,0,0,0,1'
QFont::fromString: Invalid description 'Hack,9,-1,5,400,0,0,0,0,0,0,0,0,0,0,1'
QFont::fromString: Invalid description 'Noto Sans,8,-1,5,400,0,0,0,0,0,0,0,0,0,0,1'
QFont::fromString: Invalid description 'Noto Sans,8,-1,5,400,0,0,0,0,0,0,0,0,0,0,1'

So it seems that XnView/Qt5 does not understand the new font specifications used in new KDE/Qt6. A little bit of Googling points to these pages:

https://discuss.kde.org/t/how-to-set-qt ... vianovella
https://forum.endeavouros.com/t/plasma- ... apps/52280

The solution for Qt 5 apps under KDE Plasma 6 in general is to install "plasma-integration5" package (or similar), i.e. /usr/lib/x86_64-linux-gnu/qt5/plugins/platformthemes/KDEPlasmaPlatformTheme5.so library. Unfortunately it does not affect XnView, presumably because it uses it's own distribution of Qt 5 libraries.

Out of curiosity, I tried linking this library from "/opt/XnView/lib/platformthemes":

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/opt/XnView/lib/platformthemes/KDEPlasmaPlatformTheme5.so -> /usr/lib/x86_64-linux-gnu/qt5/plugins/platformthemes/KDEPlasmaPlatformTheme5.so

but it does not work:

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QFactoryLoader::QFactoryLoader() checking directory path "/opt/XnView/platformthemes" ...
Cannot load library /usr/lib/x86_64-linux-gnu/qt5/plugins/platformthemes/KDEPlasmaPlatformTheme5.so: (/lib/x86_64-linux-gnu/libKF5GuiAddons.so.5: undefined symbol: _ZN23QWaylandClientExtensionD2Ev, version Qt_5)
QLibraryPrivate::loadPlugin failed on "/usr/lib/x86_64-linux-gnu/qt5/plugins/platformthemes/KDEPlasmaPlatformTheme5.so" : "Cannot load library /usr/lib/x86_64-linux-gnu/qt5/plugins/platformthemes/KDEPlasmaPlatformTheme5.so: (/lib/x86_64-linux-gnu/libKF5GuiAddons.so.5: undefined symbol: _ZN23QWaylandClientExtensionD2Ev, version Qt_5)"
QFont::fromString: Invalid description 'Noto Sans,8,-1,5,400,0,0,0,0,0,0,0,0,0,0,1'
QFont::fromString: Invalid description 'Hack,9,-1,5,400,0,0,0,0,0,0,0,0,0,0,1'
QFont::fromString: Invalid description 'Noto Sans,8,-1,5,400,0,0,0,0,0,0,0,0,0,0,1'
QFont::fromString: Invalid description 'Noto Sans,8,-1,5,400,0,0,0,0,0,0,0,0,0,0,1'

So, in the end, the question is: "Is there a way around this"? Can XnView be made to work with KDE Plasma 6 and honor system font settings?