add support for nix flake (I-am-Erk#2117)

.envrc

@@ -0,0 +1,4 @@
+if ! has nix_direnv_version || ! nix_direnv_version 2.1.1; then
+    source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/2.1.1/direnvrc" "sha256-b6qJ4r34rbE23yWjMqbmu3ia2z4b2wIlZUksBke/ol0="
+fi
+use flake

.gitignore

@@ -1,7 +1,6 @@
 .DS_Store
 desktop.ini
 __pycache__
-.direnv
 # generated on build
 gfx/*/tile_config.json
 
@@ -14,4 +13,10 @@ book
 # Krita
 *.png-autosave.kra
 *.kra
+*.kra~
 *.png~
+
+# Direnv & Nix
+.direnv
+result
+.local

doc/SUMMARY.md

@@ -2,6 +2,7 @@
 
 - [Installation & Building](installation.md)
   - [Windows guide](installation_windows.md)
+  - [Nix](installation_nix.md)
 - [Style guidelines](style/summary.md)
     - [General](style/general.md)
     - [Items](style/items.md)

doc/installation.md

@@ -27,10 +27,9 @@ You will need:
 - Python 3
 - [Libvips](https://libvips.github.io/libvips/install.html)
 - pyvips (install it via python pip: `pip install pyvips`) 
-- [compose.py](https://github.com/CleverRaven/Cataclysm-DDA/blob/master/tools/gfx_tools/compose.py) script from the main [Cataclysm-DDA](https://github.com/CleverRaven/Cataclysm-DDA) repository
 
 Once you have everything ready, you can build the tileset:
 ```sh
 # Assuming that you are in the root of the tileset repository
-$ python3 <path-to-compose-py-script>/compose.py gfx/UltimateCataclysm
+$ python3 tools/compose.py gfx/UltimateCataclysm
 ```

doc/installation_nix.md

@@ -0,0 +1,31 @@
+# Nix Installation
+
+Documentation of developing tileset with [Nix](https://nixos.org/). 
+
+## Build
+
+As this repository uses flakes, it's possible to build any of the tileset (not only UlitCa) using `nix build .#{name}` command. For example:
+
+```sh
+# This will build UltiCa
+nix build .#UltimateCataclysm
+
+# But this will build Mushroom Dream
+nix build .#Mushroom-Dream
+```
+
+And the result will be in *result* directory, ready to put into the game. If you want to link the result to the different directory, use `--out-link {path}` argument.
+
+## Devshell
+
+Tileset flake also provide a simple devshell with python and vips to run tools such as `compose.py` or `generate_preview.py`.
+
+```sh
+# Enter the devshell
+nix develop .
+
+# This now works
+python3 tools/compose.py --use-all gfx/UltimateCataclysm out
+```
+
+Or if you have [direnv](https://direnv.net/) enabled, it will automatically enter the devshell upon opening the repository.

flake.nix

@@ -0,0 +1,52 @@
+{
+  inputs = {
+    nixpkgs = {
+      url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    };
+    utils = {
+      url = "github:numtide/flake-utils";
+    };
+  };
+
+  outputs = { self, nixpkgs, utils }:
+    utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system;  };
+
+        requires = with pkgs; [
+          (python311.withPackages(ps: [ ps.pyvips ]))
+          vips
+        ];
+      in
+      rec {
+        # `nix build`
+        packages = (pkgs.lib.mapAttrs' (name: _: 
+          pkgs.lib.nameValuePair name (pkgs.stdenv.mkDerivation {
+            inherit name;
+            version = "master";
+            src = ./gfx/${name};
+            buildInputs = requires;
+
+            dontCheck = true;
+            dontPatch = true;
+            dontConfigure = true;
+
+            buildPhase = ''
+              python3 ${./tools/compose.py} --use-all --feedback CONCISE . compiled
+            '';
+            installPhase = ''
+              mkdir -p $out
+              cp compiled/* $out
+              for file in [ "fallback.png" "layering.json" "tileset.txt" ]; do
+                [ -f "$file" ] && cp "$file" $out ||:
+              done
+            '';
+          })
+        ) (builtins.readDir ./gfx));
+
+        # `nix develop`
+        devShell = pkgs.mkShell rec {
+          nativeBuildInputs = requires;
+        };
+      });
+}