Add functionality to change IBus panel themes with available GTK themes

[HollowMan6]

The senario of using custom theme or icon is pretty much alike the using custom font. If users want to change IBus panel theme, just tick the Use custom theme, then select a theme from the combo box. Or tick the Use custom icon, then select an icon theme from the combo box to customize page switch buttons (the arrows):

Examples

Untick the box to follow the system global gtk theme or icon theme again.

(This feature is a part of my goal in GSoC 2021 project, I used to use GTK_THEME=? ibus-daemon -r & to change IBus GTK themes with my IBus-Theme-Tools, but now I guess it's better to add this functionality to upstream since it's more intuitive.)

@hillwoodroc @qiangzhao @epico

[fujiwarat]

Thank you for the idea. I will bring back the issue later.

[HollowMan6]

Now support customizing page switch buttons (the arrows):

• 
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[fujiwarat]

I checked the code but I don't know why you need to change the theme for IBus only. The font setting is needed to enlarge the font size for IM demo.
IBus follows the current desktop theme and you can change it with the desktop tool likes gnome-tweaks, xfce4-appearance-settings.

[HollowMan6]

I checked the code but I don't know why you need to change the theme for IBus only. The font setting is needed to enlarge the font size for IM demo. IBus follows the current desktop theme and you can change it with the desktop tool likes gnome-tweaks, xfce4-appearance-settings.

@fujiwarat This PR resolves openSUSE/mentoring#158, and I can also see that a lot of people ask that ibus can have own control of themes #1548, rime/ibus-rime#101 (In Chinese, Google translation if needed), rime/ibus-rime#77 (also in Chinese).

With this feature, developers now can create an IBus specific GTK themes. (One use case is to add a background to the IBus input panel, just like fcitx, and I'm sure for most users they won't apply such kind of theme system wide, they only want the IBus panel to have it)

And finally as you know, fcitx has its own control of themes, so I would appreciate that IBus can also have that.

[fujiwarat]

    Fix and cleanup
    Making judging dark variant more general
    Set to use `gtk-*` instead of simply `*`

Please mention your changes are relative with theme in each git subject

[HollowMan6]

Thanks for your reviewing. I've squashed all the commits into one, otherwise it would be too messy to make those changes.

[fujiwarat]

Looks much better now however I asked some updates.

I like to have the links gnome-tweaks and this PR:

Add functionality to change IBus panel themes with available GTK themes

<Describe why you need this feature in IBus instead of the desktop theme tools>

https://gitlab.gnome.org/GNOME/gnome-tweaks/-/blob/b9badc47b92dd73f8cedbd2efc66cbaf3ea25773/gtweak/tweaks/tweak_group_appearance.py#L69

BUG=https://github.com/ibus/ibus/pull/2327
    
Signed-off-by: Hollow Man <hollowman@opensuse.org>

[fujiwarat]

Could you provide which UI effects the customizing icon theme? I could not find any differences in XFCE desktop.

This change effects GUI and unfortunately the change would be a little late for 1.5.26 and I will reschedule this to 1.5.27, sorry.

[HollowMan6]

Could you provide which UI effects the customizing icon theme? I could not find any differences in XFCE desktop.

It's the arrows for candidates page up and down. I've mentioned here: #2327 (comment) . It works on KDE.

[fujiwarat]

It's the arrows for candidates page up and down. I've mentioned here: #2327 (comment) . It works on KDE.

Ah, you meant the arrow buttons. Thank you. I didn't notice them when I looked at your screenshots.
Probably I think it's good to add tooltip_text for check buttons and I will add another code review.

[fujiwarat]

I'd request to add tooltip texts to explain the features.

[HollowMan6]

@fujiwarat Done! Thanks for reviewing!

[fujiwarat]

LGTM.
I will ask you to rebase patches again after 1.5.26 is released.

[cryobry]

@fujiwarat could we get this merged for 1.5.27 release go-ahead?

[fujiwarat]

The master branch is still a maintaining term for 1.5.26.
I will integrate this feature after Fedora 36 GA.
https://fedorapeople.org/groups/schedule/f-36/f-36-key-tasks.html

[fujiwarat]

@HollowMan6 Do you have a chance to rebase your patches to the latest master?
We have done internal tests with your patches recently and the status is fine.

[HollowMan6]

@fujiwarat Done rebasing! CI looks good. Thanks for reviewing the PR and tests all the way.