mozc-tool ignores KDE Qt theme

[Daniel Tang]

Mozc ignores my KDE Qt theme, and uses the ugly fallback theme.

1) The release of Ubuntu you are using, via 'lsb_release -rd' or System -> About Ubuntu

Description: Ubuntu Hirsute Hippo (development branch)
Release: 21.04

2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in Software Center

mozc-utils-gui:
  Installed: 2.26.4220.100+dfsg-4ubuntu2
  Candidate: 2.26.4220.100+dfsg-4ubuntu2
  Version table:
 *** 2.26.4220.100+dfsg-4ubuntu2 500
        500 http://archive.ubuntu.com/ubuntu hirsute/universe amd64 Packages
        100 /var/lib/dpkg/status

3) What you expected to happen

The UI should use the configured Qt theme like all Qt applications. For an example of an application with the correct theme, you can open Dolphin, and click the overflow menu, then "Configure Dolphin".

The "OK", "Apply", and "Cancel" buttons are particularly easy to compare.

4) What happened instead

The UI looks very ugly and out of place compared to the rest of the system. It looks like it's falling back to the default Qt theme. It doesn't look like a piece of software bundled with Ubuntu, but rather like downloaded 3rd-party software that bundles its own Qt like Anki (dark mode), Genymotion, Binary Ninja, and (old versions of) MultiMC.

[Daniel Tang (daniel-z-tg)]

Furthermore, the version text is impossible to read without a color picker tool.

This seems related to the Qt theme being wrong.

[Gunnar Hjalmarsson (gunnarhj)]

Thanks for your report.

Do you know if the issue is present in e.g. 20.04 or 20.10 as well?

Assuming you are using Kubuntu, I don't have access to any Kubuntu install ATM. But both Mozc Setup and About Mozc look good for me on Ubuntu 20.10 and 21.04, i.e. it honors the theme in effect, in my case Yaru which is a GTK theme.

[Daniel Tang (daniel-z-tg)]

> But both Mozc Setup and About Mozc look good for me on Ubuntu 20.10 and 21.04, i.e. it honors the theme in effect,

I spun up VirtualBox live CD VMs for those Ubuntu and at least the about box is legible.

> in my case Yaru which is a GTK theme.

mozc-tool is a Qt application. I've heard GTK theme tend to have a harder time applying to Qt applications. The icons are the proper Yaru icons though. This can be shown be changing the "Window colors" in the settings from "Standard" to "Dark".

Even in Ubuntu, mozc_tool is NOT using Yaru. It does not in fact "honour[...] the theme in effect". Only the icons are from Yaru. One place you can tell is the padding of the buttons. The padding of the buttons is different compared to that in gedit's preferences. The padding looks extremely uneven, with the "Reset to defaults" having it being overly biased towards the vertical, and the "Apply", "Cancel", and "Ok" having it biased towards the horizontal. Another place would be the radius of the corner rounding. The theme of the dialog doesn't look like Yaru, but rather looks as out of place as the theme of Altera Quartus 13.0.

[Daniel Tang (daniel-z-tg)]

> Assuming you are using Kubuntu, I don't have access to any Kubuntu install ATM

> Do you know if the issue is present in e.g. 20.04 or 20.10 as well?

I spun up Kubuntu 20.04, 20.10, and 21.04 live CD VMs. I found the theming issue is present neither in 20.04 nor 20.10. On those versions, (aside from the one minor problem of the line underneath the tab) the dialog fits in like a native KDE application. It seems like this is a regression introduced in 21.04.

The about box text is still illegible in all three versions.

Attached is the newly-found expected behaviour, as it was in 20.04 and 20.10.

[Gunnar Hjalmarsson (gunnarhj)]

Hmm.. Ok. Thanks for your investigation. As you most likely suspect, you are talking with somebody who isn't very attentive to theme stuff. :/

mozc is packaged in Debian, and Ubuntu uses the package without modifications (at least at the moment). The regression you found may well be an upstream (Google) issue. OTOH the Debian packaging is not trivial.

It would be great if you could report the issue to Debian too, to start with.

https://bugs.debian.org/cgi-bin/pkgreport.cgi?pkg=ibus-mozc

If you do, please post a link to the Debian report here for tracking purposes.

[Daniel Tang (daniel-z-tg)]

Reported as https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=985709

[Gunnar Hjalmarsson (gunnarhj)]

Thanks!