Few official Ubuntu spins (including Ubuntu itself, Xubuntu and Lubuntu) use light-locker instead of legacy screen-savers for screen locking. It might be a good idea for Ubuntu Mate devs to use that too instead of legacy mate-screensaver program or at least give a way for users to change mate-screensaver background wallpaper (there is not way to do it as far as I can tell, this https://github.com/mate-desktop/mate-screensaver/issues/55 did not work to change the background)
I do think Light-locker looks nice, an adaptation of Ubuntu's login/lock screen but for MATE would be interesting. The current login and lock screen looks quite retro from those Ubuntu 10.x days.
There is a crude way for Ubuntu MATE, change the file of /usr/share/backgrounds/ubuntu-mate-common/Ubuntu-Mate-Cold.jpg to the picture you desire. (Check the permissions are set correctly too)
I agree there should be an option somewhere to easily change the lock screen wallpaper.
Wow! It does work! Thanks, another issue though is it still uses “Zoom” as wallpaper fitting policy and that looks horrible on my dual monitor set.
Going back to light locker it is worth mentioning that using it allows to change the wallpaper for login screen, desktop and the screen locker all at the same time (at least in Ubuntu and Xubuntu). If you use mate-screensaver you have to change it separately for desktop, lightdm and screensaver and that does not seem convenient to me.
As an alternative it could be possible to write a script or something to change the wallpaper automatically for all 3 services.
A downside of dropping mate-screensaver in flavour of light-locker is that there would only be one screen saver - blank. It would lose the legacy screen savers, which I think is a retro feature that Ubuntu MATE would wish to keep – installing xscreensaver-gl and xscreensaver-gl-extra adds a whole bunch of interesting ones.
For the wallpaper situation, that problem could be solved by adding customization options to mate-tweak, like those you mentioned:
Use default wallpapers
Set wallpapers individually
Set one wallpaper for everything (desktop, lock, login)
Retrospective future is their moto so I reckon some compromises would have to be made at some time. Legacy screensaver are fun a lot of people may want to preserve those, that’s true. I also think that light-locker could be tweaked to support that as well.
As for the current state of events I don not they integrate lock screen wallpaper in mate tweak simply because the screensaver uses elevated privileges (pointed out in the link you shared, the one by @Wimpy). I think they would rather do it as a part of LightDM Greeter settings (possibly renaming that to LightDM and Screensaver settings or something).
Back in the day Ubuntu did not use LightDM (I’m pretty sure it used GDM as a part of Gnome2 environment). Now that we have Ubuntu Mate which uses LightDM, Light-Locker is logical choice because it was sort of meant to be used ensemble with LightDM and they both integrate nicely. Screen-savers are still a solid point for many to leave mate-screensaver. I think they have to create a poll or something for that.
