Candidate window doesn't follow QT theme on Linux

[BrianAllred]

Description

Candidate window doesn't follow the specified QT theme on Linux, which can make the candidates difficult to read and also cause eye strain (if it defaults to a bright color like white).

Steps to reproduce

Steps to reproduce the behavior:

1. Set environment variable QT_QPA_PLATFORMTHEME to a dark theme.
2. Type using mozc so that the candidate window appears.

Expected behavior

The candidate window appears using the correct theme.

Actual behavior

The candidate window appears using an incorrect theme

Screenshots

Incorrect theming:

For example, this is what anthy looks like:

Version or commit-id

mozc-2.29.5111.102-1.2

Environment

• OS: openSUSE Tumbleweed using latest Gnome Wayland
• IMF: ibus
• Related Applications: all

Investigations

• Whether this issue happens on both Ibus and other IMF (e.g. Fcitx, uim).
  • N/A
• Whether this issue happens on other IMEs (e.g. Anthy, SKK).
  • no
• What applications this issue happens on (e.g. Chromium, gedit).
  • all
• What applications this issue does not happen on (e.g. Chromium, gedit).
  • N/A
• (optional) What versions or commit-ids this issue did not happen on
  (e.g. Mozc-2.28.4960.100+24.11.oss).
  • N/A

Additional context

Add any other context about the problem here.

[yukawa]

Thank you for the report. Supporting dark theme has been our to-do list for long time.

For your case, you can uninstall ibus-mozc-candidate-window package from our environment to use IBus' default candidate window, which is what Anthy is using in your screenshot.

The following document also describes how to use IBus' default candidate window rather than Mozc's one.
https://github.com/google/mozc/blob/master/docs/configurations.md#use-the-default-ibus-candidate-window

As for our long term plan, I guess we may want to rely on the corresponding settings in XDG Desktop Portal rather than relying on QT_QPA_PLATFORMTHEME, which cannot handle dynamic theme update. Here are several examples in other projects.

• GNOME: https://blogs.gnome.org/alicem/2021/10/04/dark-style-preference/
• KDE: https://invent.kde.org/plasma/xdg-desktop-portal-kde/-/merge_requests/49
• Chromium: https://bugs.chromium.org/p/chromium/issues/detail?id=998903
• Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1734934

I'm going to convert this to discussion as it's a bit unlikely to just use QT_QPA_PLATFORMTHEME anyway.

[yukawa]

I'm going to convert this to discussion as it's a bit unlikely to just use QT_QPA_PLATFORMTHEME anyway.

Actually, looks like Qt 6.2 and later have already been reading XDG Desktop Portal settings.

• qt/qtbase@3c6b61a
• https://codereview.qt-project.org/c/qt/qtbase/+/396655

[pancaek]

Hello, I am facing a similar issue with mozc on Manjaro (ibus-mozc-2.29.5200.102-1)
When following the solution described in https://github.com/google/mozc/blob/master/docs/configurations.md#use-the-default-ibus-candidate-window, I receive the error
E0000 00:00:1693094425.842190 36735 text_format.cc:383] Error parsing text-format mozc.ibus.Config: 10:15: Message type "mozc.ibus.Config" has no field named "mozc_renderer".

My ibus_config.textproto looks like this when I receive the error

engines {
  name : "mozc-jp"
  longname : "Mozc"
  layout : "default"
  layout_variant : ""
  layout_option : ""
  rank : 80
  symbol : "あ"
}
engines {
  name : "mozc-on"
  longname : "Mozc:&#x3042"
  layout : "default"
  layout_variant : ""
  layout_option : ""
  rank : 99
  symbol : "あ"
  composition_mode : HIRAGANA
}
engines {
  name : "mozc-off"
  longname : "Mozc:A_"
  layout : "default"
  layout_variant : ""
  layout_option : ""
  rank : 99
  symbol : "A"
  composition_mode : DIRECT
}
mozc_renderer {
  # This means IBus' candidate window is always used.
  enabled : False
}
active_on_launch: True

[pancaek]

This persists after updating the PKGBUILD to use the latest commit from git

[yukawa]

This persists after updating the PKGBUILD to use the latest commit from git

Hmm. That's strange. Can you restart your machine to see if the issue persists?

[yukawa]

BTW, MOZC_IBUS_CANDIDATE_WINDOW environment variable described in the previous revision of the document should still work.

https://github.com/google/mozc/blob/89c70080d0102e8ed23cae6c05b535dedf506de4/docs/configurations.md#use-the-default-ibus-candidate-window

[pancaek]

Strangely, restarting did not fix the issue. I used the old method, and that does seem to be working.

[yukawa]

Strangely, restarting did not fix the issue. I used the old method, and that does seem to be working.

Then it sounds like you are still using an old build that doesn't have this commit: 65a5d1f. In my local testing environment (Ubuntu 22.04), mozc_renderer setting is working as intended. My suggestion is just relying on MOZC_IBUS_CANDIDATE_WINDOW for now and tryingmozc_renderer out when you receive a new package release in your distribution.