Tested with Plasma 5.12
Your desktop just got a real make up with this awesome login screen. NixOS reduces the clutter of your greeter and leaves you with a clean, easy to use, login interface with a modern yet classy touch.
Please share some love and up vote if you like this theme!
Also be sure to check out my window decorations that surely will fit well with your new login screen:
Install via "System Settings > Startup and Shutdown > Login Screen (SDDM) > Get New Theme". This is a modified breeze theme so don't try to use it with anything other than KDE Plasma and SDDM. It probably won't work.
The background can be changed to anything you want on the right hand side in "System Settings > Startup and Shutdown > Login Screen (SDDM)". Select the large green button next to "Background:"
The "Different User" button was removed. It is confusing to new users and I consider anybody who wants to login as root, or whatever, capable of doing so through TTY. The blur filter requires OpenGL. Please comment bugs that may occur.
A word on tweaking the theme:
Depending on the colors of your avatar image you may see a few grey pixels around your image. This is caused by the anti-aliasing of the Qt filter mixing the color of the opacity mask (a light grey, which usually blends well in most situations) with the image itself. If this happens to you and you don't want to change your image you can go to /usr/share/sddm/themes/nixos/components/artwork and change the color of "mask.svg" to something that resembles better the colors of the image in question (do not change the opacity of the mask!). If there are several users on the machine this may effect the other user images in a negative manner though.
Apart from this I consider this theme visually well balanced as is. Still so if you have a very big screen the fonts may get small (some feedback on this would be great!). If this becomes an issue you can search the files in the above mentioned theme folder (nixos) for entries that say "font.pointSize:" Just be aware that the upper right corner consists of the following elements: KeyboardButton.qml, Battery.qml and Clock.qml. So if you change any of these in size you may want to adapt the others as well.