Hello, I’m pretty new to NixOS :))) and I wondered how can I install picom, as the usual nix-env -iA nixos.picom doesn’t work (didn’t find anything on internet).
Also, I have a problem with my touchpad :c, sometime, he freezes for a minute and he’s back to normal, but all I can do is waiting, although I can use my keyboard. I tried using an external mouse, but it doesn’t work, but that’s another problem that I can figure out on my own I think.
Well, basically I think that’s all for my problems at the moment.
I must specify that I’m running on NixOS 20.03 with i3 as window manager and no desktop environment. I tried building it from the source code but the meson command doesn’t work perfectly, don’t know why. If it has anything to do with my problem, I can surely put the ouput of the command here, let me know. Thank you for taking time to read it and eventually answer 
In what way does it not work?
If it missing, what does nix-channel --list show?
It simply tells me error: attribute 'picom' in selection path 'nixos.picom' not found. And nix-channel --list returns home-manager https://github.com/rycee/home-manager/archive/release-19.09.tar.gz
You need to add the nixos channel.
nix-channel --add https://nixos.org/channels/nixos-20.03 nixos
nix-channel --update
The root user and your normal user have separate nix-channel configs.
didn’t know that haha thank you, now I have to figure out the problem about the touchpad…
You shouldn’t install picom with nix-env, you should use the nixos option in configuration.nix NixOS Search - Loading...
sorry, I’m pretty new, what do I have to put in my configuration.nix then ?
services.picom.enable=true; would be a good starting point.
yeah that’s what I thought, thanks c: and last question, is compton.service in fact picom.service ?
services.compton is an alias for services.picom