LightDM Greeter Setup
LightDM is new Display Manager (DM) which seems to be widely adopted across distributions. It is not required to use LightDM at all Razor-qt will work out of the box from most displaymanagers
Update or insert in(to) your /etc/lightdm/lightdm.conf, in the SeatDefaults section, this line:
greeter-session=lightdm-razor-greeter
The file /etc/lightdm/lightdm-razor-greeter.conf allows for a few configurations of lightdm-razor-greeter (background-image, positioning of loginform). The configuration options are documented in that file.
To enable LightDM as a DM instead of kdm/gdm/xdm set appropriate value in the DISPLAYMANAGER variable with YaST for it (module Sysconfig Editor) or edit /etc/sysconfig/displaymanager manually.
DISPLAYMANAGER="lightdm"
Then restart the rcxdm service (or your computer).
To install lightdm, do
sudo pacman -S lightdm
To set lightdm as the displaymanager do (assuming you use the default init system, systemd):
sudo systemctl enable lightdm.service
If you already have an displaymanager installed, you will need to disable that first, e.g:
sudo systemctl disable xdm