Add wallpapers for other desktops

[yselkowitz]

Per discussions today, we want to find a way to create the symlinks needed for other desktops in a systematic fashion that can easily be added to each EL distro's own logos/backgrounds packages, so that it can be used by default in EPEL-shipped distros, starting with KDE.

• Create /usr/share/backgrounds/default.(jxl|png|xml) etc. to replace Fedora's desktop-backgrounds-compat for Xfce/MATE/etc.
• Create a structure under /usr/share/wallpapers for KDE/LXQt.

[yselkowitz]

I have updated my proof of concept at https://copr.fedorainfracloud.org/coprs/yselkowitz/backgrounds-v2/

The basic principles of this "API" are:

• Fedora uses .jxl for its default wallpaper, all ELs (as of 10) use .png.
• If a future EL major version adds support for e.g. .jxl, then all of them must use the same format as RHEL.
• Additional wallpapers can be in other formats (e.g. .jpg) that are supported by the OS.
• Symlinks to the default wallpaper images are located at /usr/share/backgrounds/default{,-dark}.$SUFFIX, and optionally(?) default.xml for time-of-day support, and are included by a package which Provides: system-backgrounds-compat
• When setting these filenames in packages, the suffix should be conditional on a macro rather than relying on build-time detection.
• The GNOME background properties XML is located in /usr/share/gnome-background-properties and is included in a package which Provides: system-backgrounds-gnome.
• Symlink to the default KDE wallpaper directory is located at /usr/share/wallpapers/Default and is included by a package which Provides: system-backgrounds-kde. A script can be used to create these symlinks based on GNOME BG XML.
• All desktop packages' dependencies must use system-backgrounds-* names, and file references to the default backgrounds must use these locations only.
• /usr/share/backgrounds/images is deprecated.

For the backgrounds themselves, the following changes are necessary:

• Fedora desktop-backgrounds: add a -kde subpackage which requires f43-backgrounds-kde, provides system-backgrounds-kde and contains a /usr/share/wallpapers/Default symlink to the F43 directory in the same tree.
• ELN fedora-eln-backgrounds: provides system-backgrounds-*, provides/obsoletes desktop-backgrounds-{compat,gnome,kde}, create the default symlinks, and generate the KDE directory structure.
• CentOS Stream centos-logos: Ditto.

For KDE, the changes are as follows:

• kde-settings: stop providing the /usr/share/wallpapers/Fedora symlink, require system-backgrounds-kde instead of f43-backgrounds-kde
• plasma-desktop/sddm-breeze: Adjust requires and set file extension by macro conditional rather than file test
• plasma-workspace/plasma-lookandfeel-fedora: use Default instead of Fedora

Other desktops will require various changes to conform to this "standard", with the most common change being the switch from desktop-backgrounds-compat to system-backgrounds-compat.

[Conan-Kudo]

This probably needs a Fedora 44 change document to implement, but it seems reasonable. We'll have to actually implement it once the Change is accepted to see how it rolls out.

[Conan-Kudo]

Note that I do expect EL11 backgrounds to use JXL since GNOME now recommends it due to JXL supporting embedded color profile data.

[yselkowitz]

This probably needs a Fedora 44 change document to implement, but it seems reasonable. We'll have to actually implement it once the Change is accepted to see how it rolls out.

Agreed, and once made we should probably also bring this to FRCL.

[yselkowitz]

Another detail: KDE wallpaper symlinks should include 1440x2960 and 5120x2880 for Plasma Mobile Initial Setup. (The use of .jxl instead of .png will need to be addressed there too.)

[yselkowitz]

Moving further higher-level discussion to fedora-eln/eln#341; leaving this for the implementation in fedora-eln-backgrounds.