No smooth transition from lightdm-gtk-greeter to desktop environment

Actually there shouldn't be a big rupture visually, as lightdm-gtk-greeter uses the user's wallpaper (at least if the service that sets the wallpaper in the session supports accountsservice, e.g. in Xubuntu that is the case). In Xubuntu the transition is that the greeter disappears and the elements of the desktop appear with the wallpaper remaining the same.

Not sure where you'd wanna implement a fade there. Theoretically the greeter could do a fade-to-black, but that might not even be desirable (see the transition in Xubuntu described above) and the result depends much on what the session does. A cross-fade isn't really doable as far as I can tell.

I understand that visual rupture is unnoticeable if greeter and session wallpapers match like, as you say, in Xubuntu.

On the other hand, "modular" configurations like the one I'm running in Arch Linux should be taken into account. i.e.: Different backgrounds set in Cinnamon configuration and lightdm-gtk-greeter.conf. Also, under multiuser layouts, having a common greeter wallpaper and one different wallpapers for each user is a common situation.

Provided that, I still think it'd be a great possibility. My thoughts were using a greeter fade-out alpha channel effect, like the one from KDE KSplash to the desktop once it has finished loading. I don't know if it's possible and I'm aware that it'd require hours of developping, though.

Thanks a lot for your attention, I didn't expect such a quick answer.

@ochosi

  I'm looking at slick-greeter and trying to understand why the greeter to desktop involves a black-screen transition period. lightdm-gtk-greeter doesnt have this black-screen transition.

Any hints that you can share how lightdm-gtk-greeter transitions from the greeter background image to the desktop image?