Use current user desktop background as greeter background

[Tank-Missile]

Either through gsettings, xfconf, or whatever is used to hold the current desktop background location, add the ability to use the desktop background as the greeter background. If the desktop background is changed while the session is locked via variety or a background changing script, the greeter background should also change accordingly. If I understand how lightdm works, it isn't able to read images inside the /home folder. Luckily, variety is able to copy the current background to a usable location and set gsettings/xfconf accordingly. From looking at other available greeters, they suffer from this same limitation. Clicking on a different user should show that user's current background.

[NoiSek]

When Variety syncs the current background to a directory, are you saying that it keeps concurrent copies of the current background for each user or that it switches only after the active user has changed?

If Variety can keep the background synced to the theme directory (manually configured per user), this is technically doable, but if the above isn't the case I'm a little hesitant to add a feature that requires manual configuration and wouldn't fully work as expected.

[Tank-Missile]

Variety will copy the background to a public folder and change its permissions to make it readable by all. After switching to another background, it will delete the last one from the folder. Now, you would think this means only the current background is kept in the folder, but unfortunately this is not the case. It keeps the last and current background in the folder (might be a bug). Each user can configure variety to copy the background to a different location.

What I'm proposing could benefit all webkit2 greeters, so I might make a request upstream. The problem is not every desktop environment uses gsettings/xfconf. Cross-desktop functionality is important! AccountsService may come in handy for the job.

[NoiSek]

I think this could be a useful feature, but I'm still iffy on supporting a feature like this until it would be easier for both me as the developer to implement and users as a whole to configure. Couple of potential pitfalls here, and I'm not a fan of unpredictable behavior.

The last and current wallpaper both being saved there is probably to support crossfading, also.

Deferring this one until there's either upstream support or significantly more interest in this feature.

[JezerM]

Actually, this is possible, but not the most convenient thing to have. LightDM GTK+ Greeter does something similar, accessing to the background property each LightDMUser object has. But as far as I've seen, this property is only available when using a complete Desktop Environment like Ubuntu, XFCE, KDE, etc. However, when using something else, like a simple Window Manager, this property won't be available. I guess this is because of gconf or something similar.

Furthermore, I've seen LightDM can surpass the "no access to home" limitation with the user background property, so I guess it won't be a problem to set a home-image as the wallpaper and access it from LightDM. (Maybe I'm misremembering this)

Anyway, it could be easily implemented with user.background, checking if it's not an empty string to set the background, if else then go with the default theme behavior.