Provide a DBus API to set wallpaper
Currently, there are two applications that allow the user to set a wallpaper: Nautilus and GNOME Photos.
Each application has a different implementation, let's take Nautilus for example:
- Creates a Wallpaper directory under ~/Photos
- Copies the files there even if the file is already there
GNOME Photos has a different behavior too. The idea is to have something unified and let GCC handles the caching and all the rest.
An issue was opened a long time ago on Nautilus https://bugzilla.gnome.org/show_bug.cgi?id=688812 and there was some discussion about having a DBus API to handle the set wallpaper stuff instead of changing the gsettings by the other application.