Delete onNixOS attribute

[haruki7049]

• Init nix flakes #208

onNixOS dusturbs creating flake.nix, because pkgs.callPackage ./. { }; is almost used in flake.nix, as:

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
    flake-parts.url = "github:hercules-ci/flake-parts";
  };

  outputs =
    inputs:
    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
      systems = [
        "x86_64-linux"
        "aarch64-linux"
      ];

      perSystem = { pkgs, ... }:
        let
          simila = pkgs.callPackage ./. { };
        in
        {
          packages = {
            inherit simula;
          };

          checks = {
            inherit simula;
          };
        };
    };
}

---

I think that Simula must run on the machine installed Nix with same code, so onNixOS must be deleted. Also, I think devBuild must be deleted by this reasons.

[haruki7049]

I don't know why did SimulaVR team create this attribute, so please tell me the reasons if you know that.

[haruki7049]

This definition is using onNixOS value

Simula/Simula.nix

Line 34 in c077a5f

vulkan-loader-custom = if onNixOS then vulkan-loader else (callPackage ./nix/vulkan-loader.nix { });

[georgewsinger]

non-NixOS machines require Simula to run with nixGLIntel or nixGLNvidia.

[haruki7049]

Was there any solution other than nixGL?

[georgewsinger]

None that we could find. Possible that things have changed since then.

[haruki7049]

I checked that pkgs.godot_4 is unable to run on Ubuntu-24.04.1. At that time, it said an error about OpenGL.

Nix files and log: https://gist.github.com/haruki7049/82d150c45e064ec490eec84a91bf2508

However, I think that nixGL should be used by client side only, because in nixpkgs repo, pkgs.godot_4 uses pkgs.libGL but nixGL is not used.

[haruki7049]

Then I think that nixGL should be deleted in SimulaVR/Simula repo, such as /utils/GetNixGL.sh. Because nixGL installation should do by user.