I had installed Kubuntu 16.04 Xenial just in the official release day, April 21, and found extremely unpleasant thing: the library gtk3-engines-oxygen , which provides Oxygen theme support for GTK3 applications is absent. I failed to find it in Launchpad as well. Version for Wily could not be installed in Xenial, and also I failed to compile it from sources of oxygen-gtk3-1.4.1 available in Launchpad.

Can we hope for appearing it in Xenial in foreseeable future? For me it is important question, because on it my decision will depend whether to stay in future in some Kubuntu-based distribution (currently I am using Mint 17.3 based on Trusty, but some day the need for more actual distribution could arise) or move to openSuse Leap, where everithyng is OK with Oxygen theme for all kind of software. The situation when the Oxygen theme is not supported for one of the most common software group (where Firefox 46 belongs for example) seems to me absolutely unacceptable.

Hello,

The Gtk developers effectively removed the functions Oxygen relied upon from Gtk 3.14. No one ported the theme to the new API yet, and it probably won't happen. See also the interesting discussion in bug #340288 and Gtk bug #735211.

So the short answer is : most probably never.

Louis

But in openSUSE everithyng is OK, in KaOS also! Only Kubuntu lacks GTK3 support among well-known current distributions.

Anyway, if Breeze theme was successfully ported, why it is impossible for Oxygen? Is there any sufficient technical differerence between them in this respect?

Menak Vishap wrote:But in openSUSE everithyng is OK, in KaOS also!

No, it isn't.
gtk3-oxygen does not work with GTK>=3.16.
And openSUSE Leap 42.1 does come with 3.16.7.

That it works with Firefox in openSUSE is because openSUSE's Firefox still uses GTK2, while Ubuntu probably switched to GTK3 (like Mozilla upstream with v46).

Anyway, if Breeze theme was successfully ported, why it is impossible for Oxygen? Is there any sufficient technical differerence between them in this respect?

Yes.
Oxygen was a theming engine (to be able to share the code with the Qt style), and support for theming engines has been removed completely in GTK 3.16.

The Breeze GTK theme has been created from scratch by someone, using CSS stylesheets.
The same should of course be possible with Oxygen too, but someone would have to do it.
And it would basically mean to do a full theme from scratch, without being able to reuse much from the existing one...

wolfi323, thank you for popular and exact explanation! The situation now is quite clear for me, and it is indeed much worse then I suspected. The problem is systemic, and I see that Kubuntu team is unlikely to be able and willing to solve this.

But I still very hope that KDE developers will have time and enthusiasm to port the Oxygen GTK theme to CSS one day, when all more urgent and important tasks will be solved, and I would like to hope that it could happen until April 2019. For now the Graybird theme seems to be more-or-less acceptable replacement.

And in general this situation pushed me for some reflection. It had revealed the weak point of all "secondary" KDE distributions like Kubuntu, based on some non-KDE distribution, which consider another environment as "mainstream". It restricts developers' possibility to "workaround" in such situation (in this case - use GTK2 instead of GTK3 in Firefox, use older GTK3 version, use Plasmazilla, etc.), because they depend on "mainstream" distribution (Ubuntu in this case). The issue with GTK theme is just minor thing, but tomorrow something more sufficient can happen, that could break Plasma work in future Kubuntu releases. For me it is a signal that, may be, there is a reason to look in future for some distribution which considers KDE Plasma as its main environment a priori (like openSUSE Leap, KaOS, Chakra, etc.) instead of future Kubuntu releases.

I started a base for it, just to show the windows of Firefox and Filezilla correctly, but it should give you a head start.
Just save this code in: /home/USERNAME/.config/gtk-3.0/gtk.css

Code: Select all

/* Oxygen:
   background-color: #d6d2d0;
   background-image: linear-gradient(to bottom, #e2dfde, #c2bbb7)

   https://quickgit.kde.org/?p=breeze-gtk.git
   https://git.gnome.org/browse/gtk+/tree/gtk/theme/Adwaita/gtk-contained.css
*/

.background, .toolbar, column-header .button, .menubar {
   background-color: #d6d2d0;
}

.menu {
   background-color: #d6d2d0;
   background-image: linear-gradient(to bottom, #e1dfdd, #c2bbb8);
   box-shadow: 0 0 2px 1px #f7f7f7 inset;
   border-radius: 6px;
}
GtkComboBox .menu {
   background-color: #fff;
   background-image: none;
   box-shadow: none;
   border-radius: 0;
}