Add support for Qt client side window decorations (CSD)

[cwmke]

Fedora 32
Gnome 3.36.1

I noticed certain QT based apps like Gwenview, KeepassXC and the Anki flatpak don't hide their titlebars despite Hide windows titlebars being set to Always. I searched Issues but didn't find anything similar. This extension is really spectacular. Many thanks for all of your efforts. I don't know if the below log from opening Gwenview is at all related but figured it can't hurt.

QSocketNotifier: Can only be used with threads started with QThread

(gwenview:234269): Gtk-WARNING **: 10:29:46.705: Theme parsing error: colors.css:71:44: Invalid number for color value

(gwenview:234269): Gtk-WARNING **: 10:29:46.705: Theme parsing error: colors.css:72:44: Invalid number for color value

(gwenview:234269): Gtk-WARNING **: 10:29:46.705: Theme parsing error: colors.css:74:53: Invalid number for color value

(gwenview:234269): Gtk-WARNING **: 10:29:46.705: Theme parsing error: colors.css:75:53: Invalid number for color value

(gwenview:234269): Gtk-WARNING **: 10:29:46.705: Theme parsing error: colors.css:76:56: Invalid number for color value

(gwenview:234269): Gtk-WARNING **: 10:29:46.705: Theme parsing error: colors.css:77:65: Invalid number for color value
kf5.kwidgetsaddons: Invalid pixmap specified.
QTimeLine::setDuration: cannot set duration <= 0
kf5.kwidgetsaddons: Invalid pixmap specified.
QTimeLine::setDuration: cannot set duration <= 0
kf5.kwidgetsaddons: Invalid pixmap specified.
QTimeLine::setDuration: cannot set duration <= 0
kf5.kwidgetsaddons: Invalid pixmap specified.
QTimeLine::setDuration: cannot set duration <= 0
kf5.kwidgetsaddons: Invalid pixmap specified.
QTimeLine::setDuration: cannot set duration <= 0
kf5.kio.core: "Could not enter folder tags:/."
kf5.kio.core: "Could not enter folder tags:/."

And here's a couple lines from Anki's cli output.

qt: Using the 'xdg-shell' shell integration
qt: Wayland does not support QWindow::requestActivate()

[jonian]

Thanks for the report @cwmke, I can confirm that the issue is present in QT applications on Wayland installed with flatpak. Not sure I can fix it though.

I do not use flatpak, so this is not a priority issue for me and I do not have too much free time to investigate this.

I'm tagging the issue as help-wanted, in case someone can fix this.

[cwmke]

Sounds good. Just to clarify for anyone interested in taking a look, I think it's QT applications in general. Gwenview was installed with the package manager; not flatpak.

[jonian]

@cwmke I tested only with KeepassXC (flatpak and package manager). Is there any other application that has this issue when installed through the package manager? Gwenview has a lot of KDE dependencies.

[cwmke]

transmission-qt, the torrent application, installed from the repos also has the issue. I would think it has significantly less dependencies than Gwenview.

[jonian]

transmission-qt works without issues for me.

[jonian]

After some testing, I think it is an issue with all QT applications in wayland. The QT applications that do not have the issue use the xwayland backend.

@cwmke is the issue present if you start transmission with:

env QT_QPA_PLATFORM=xcb transmission-qt

[cwmke]

That does the trick for hiding them. This is a good workaround for the time being. Thanks!

[jonian]

In case you don't know you can make that permanent by adding to /etc/environment:

QT_QPA_PLATFORM=xcb