Support a reproducible build via Nix

.gitignore

@@ -1 +1,6 @@
 build
+
+# Nix
+.direnv
+.envrc
+result

README.md

@@ -34,6 +34,19 @@ If not, you'll need to provide the path to the Slang compiler with
 
 The executable should then be `build/demo`.
 
+#### Nix
+
+If you use Nix, no need to install Slang or other dependencies; use these
+commands in your clone of this repo to do a reproducible build and run it:
+
+```sh
+nix build       # flakes must be enabled
+result/bin/demo # outside of NixOS, you may need https://github.com/nix-community/nixGL
+```
+
+Alternatively, you can use `nix develop` to enter a shell with all necessary
+dependencies, then run the same `cmake` build commands listed above.
+
 ### Windows
 
 1. Install [CMake](https://cmake.org), [Ninja](https://ninja-build.org), [Visual Studio 2022](https://visualstudio.microsoft.com/vs/) (Community edition is fine, we just need the MSVC compiler from this), [Python](https://www.python.org/), [LLVM](https://releases.llvm.org/) and [VCPKG](https://vcpkg.io/en/).

flake.nix

@@ -0,0 +1,50 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+    self.submodules = true;
+  };
+  outputs =
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+        nativeBuildInputs = [
+          pkgs.cmake
+          pkgs.python3
+          pkgs.python3Packages.libclang
+          pkgs.shader-slang
+        ];
+        buildInputs = [
+          pkgs.SDL2
+          pkgs.vulkan-headers
+          pkgs.vulkan-loader
+        ];
+        CPATH = "${pkgs.glibc.dev}/include";
+      in
+      {
+        defaultPackage = pkgs.stdenv.mkDerivation {
+          name = "slang-simple-vulkan";
+          src = ./.;
+          strictDeps = true;
+          inherit nativeBuildInputs buildInputs CPATH;
+          installPhase = ''
+            mkdir -p $out/bin
+            cp *.spv demo $out/bin/
+          '';
+        };
+        devShell = pkgs.mkShell {
+          inherit buildInputs CPATH;
+          nativeBuildInputs = nativeBuildInputs ++ [
+            pkgs.clang-tools
+            pkgs.nixfmt-rfc-style
+          ];
+        };
+      }
+    );
+}