graphics driver-specific bits in nix config

configuration.nix

# ...

  boot.extraModprobeConfig = ''
    options i915 alpha_support=1
  '';  

  hardware.nvidia = {
    optimus_prime = {
      enable = true;
      nvidiaBusId = "PCI:1:0:0";
      intelBusId = "PCI:0:2:0";
    };
    modesetting.enable = true;
  };
 
  # if we do not use optimus above (?)
  # hardware.nvidiaOptimus.disable = true;
  # hardware.opengl.extraPackages = [ pkgs.linuxPackages.nvidia_x11.out ];
  # hardware.opengl.extraPackages32 = [ pkgs.linuxPackages.nvidia_x11.lib32 ];

  # On 64-bit systems, whether to support Direct Rendering for 32-bit
  # applications (such as Wine). This is currently only supported for
  # the nvidia and ati_unfree drivers, as well as Mesa.
  hardware.opengl.driSupport32Bit = true;
 
  services = {
    xserver = {
      # "intel" needs i915 alpha flag above
      #videoDrivers = [ "intel" "nvidia" ];
      videoDrivers = [ "nvidia" ];
    };

# ...