bglga/flake.nix

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    flake-utils.url = "github:numtide/flake-utils";
    rust-overlay = {
      url = "github:oxalica/rust-overlay";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs =
    {
      nixpkgs,
      flake-utils,
      rust-overlay,
      ...
    }:
    flake-utils.lib.eachDefaultSystem (
      system:
      let
        overlays = [ (import rust-overlay) ];
        pkgs = import nixpkgs { inherit system overlays; };
        runtimeLibs = with pkgs; [
          libx11
          libxcursor
          libxi
          libxkbcommon
          libxcb
          vulkan-loader
          glfw
        ];

        takeScreenshots = pkgs.writeShellApplication {
          name = "take-screenshots";
          runtimeInputs = with pkgs; [
            xorg-server
            imagemagick
            coreutils
          ];
          text = ''
            set -euo pipefail

            if [ "$#" -lt 4 ]; then
              cat >&2 <<'USAGE'
            Usage: take-screenshots EXE NUM DELAY_START PAUSE_INBETWEEN [OUTPUT_DIR]

              EXE              path to executable to launch
              NUM              number of screenshots to take
              DELAY_START      seconds to wait after launching EXE before first shot
              PAUSE_INBETWEEN  seconds between consecutive shots
              OUTPUT_DIR       output directory (default: current directory)
            USAGE
              exit 1
            fi

            EXE=$1
            NUM=$2
            DELAY_START=$3
            PAUSE=$4
            OUTDIR=''${5:-.}

            mkdir -p "$OUTDIR"

            # Locate lavapipe (software Vulkan) ICD; needed because Xvfb has no GPU.
            LVP_ICD=
            for c in \
              "${pkgs.mesa}/share/vulkan/icd.d/lvp_icd.x86_64.json" \
              /run/opengl-driver/share/vulkan/icd.d/lvp_icd.x86_64.json
            do
              if [ -f "$c" ]; then LVP_ICD=$c; break; fi
            done
            if [ -z "$LVP_ICD" ]; then
              echo "take-screenshots: could not locate lavapipe Vulkan ICD" >&2
              exit 1
            fi

            # Pick a free X display.
            DISPLAY_NUM=99
            while [ -e "/tmp/.X$DISPLAY_NUM-lock" ] || [ -e "/tmp/.X11-unix/X$DISPLAY_NUM" ]; do
              DISPLAY_NUM=$((DISPLAY_NUM + 1))
            done

            Xvfb ":$DISPLAY_NUM" -screen 0 800x900x24 \
              +extension GLX +extension RANDR +render -ac &
            XVFB_PID=$!

            GAME_PID=
            cleanup() {
              if [ -n "$GAME_PID" ]; then
                kill "$GAME_PID" 2>/dev/null || true
                wait "$GAME_PID" 2>/dev/null || true
              fi
              kill "$XVFB_PID" 2>/dev/null || true
              wait "$XVFB_PID" 2>/dev/null || true
              rm -f "/tmp/.X$DISPLAY_NUM-lock"
            }
            trap cleanup EXIT

            sleep 0.5

            export DISPLAY=":$DISPLAY_NUM"
            export VK_ICD_FILENAMES=$LVP_ICD
            export LD_LIBRARY_PATH="${pkgs.lib.makeLibraryPath runtimeLibs}''${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}"

            "$EXE" &
            GAME_PID=$!

            sleep "$DELAY_START"

            for i in $(seq 1 "$NUM"); do
              if ! kill -0 "$GAME_PID" 2>/dev/null; then
                echo "take-screenshots: process exited before screenshot $i" >&2
                exit 1
              fi
              out=$(printf "%s/shot-%03d.png" "$OUTDIR" "$i")
              import -window root "$out"
              echo "$out"
              if [ "$i" -lt "$NUM" ]; then
                sleep "$PAUSE"
              fi
            done
          '';
        };
      in
      {
        devShells.default = pkgs.mkShell {
          buildInputs =
            with pkgs;
            [
              (rust-bin.stable.latest.default.override {
                extensions = [
                  "rust-src"
                  "rust-analyzer"
                ];
              })
              pkg-config
              alsa-lib.dev
              udev.dev
            ]
            ++ runtimeLibs;

          LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath runtimeLibs;
        };

        apps.take-screenshots = {
          type = "app";
          program = "${takeScreenshots}/bin/take-screenshots";
        };
      }
    );
}