ElixirDoom

Doom, written in Elixir, played in a terminal. The renderer, the BSP, collision, line of sight and the state machines are Cauldron's (cauldron_2d); this package is the game: reading a WAD, and Doom's own rules for things, weapons, monsters, doors, lifts, switches, pickups and levels.

mix deps.get
mix doom --wad path/to/DOOM1.WAD
mix doom --wad path/to/DOOM.WAD --level E2M1 --skill 4

No WAD is included. The shareware DOOM1.WAD may be passed on unchanged; the registered and commercial WADs may not. Point --wad at one you have, or set DOOM_WAD to its path or DOOMWADDIR to its directory.

On a terminal that keeps images (kitty, Ghostty, WezTerm, iTerm2) the picture is drawn at twice Doom's 320×200 and the terminal scales it to the window, so a small font gives more room without a blurrier picture. --picture (or CAULDRON_PICTURE, or config :cauldron_2d_drafter, picture: "..." in a config/runtime.exs) chooses otherwise, with any of these comma separated: native draws at Doom's own size times the largest whole number that fits the window, native:N at N times, size:WxH sets the size itself, png sends each frame as a PNG (about a third smaller, for play over ssh, at more CPU), swap replaces each frame without a blank between, and none draws at the window's cells instead. The default is native:2,swap.

Keys

Esc opens Doom's own menu, drawn from the WAD's pictures; the game pauses while it is open. New game picks the episode and skill; options holds end game, messages, graphic detail (low draws the view half as wide), screen size (Doom's border around a smaller view, or no status bar at the largest), mouse sensitivity, sound and music volume, and controls, where keys and mouse buttons are bound and the mouse switched on; read this shows the help screens; quit asks as Doom asks. Loading and saving say they are not part of this game. With the mouse on, moving it left and right turns, the left button fires, the right button runs, and the wheel picks the previous and next weapon.

A controller works too: the left stick walks and strafes and the right stick turns, each as far as it is pushed; the right trigger fires, the left trigger or pressing the left stick runs, A or X uses, the bumpers change weapon, Back shows the automap and Start the menu, where the d-pad moves, A chooses and B goes back.

A dead player presses F to start the level again. Between levels, F or Space goes on.

What is here

• every shareware level, E1M1 to E1M9, with secret exits, and the registered episodes' bosses and their exits
• the player's movement, view height and bob, running, sliding along walls, steps and drop-offs
• fist, chainsaw, pistol, shotgun, chaingun, rocket launcher, plasma rifle and BFG, with Doom's aiming, spread and refire
• zombiemen, sergeants, imps, demons and spectres, lost souls, cacodemons, barons, the Cyberdemon and the Spider Mastermind: looking, hearing through open doors, chasing, melee and missile attacks, pain, deaths and dropped weapons
• doors (keyed and timed), lifts, rising and falling floors, crushers, stairs, lights that flicker, strobe and glow, switches, teleporters, damaging floors and secrets
• pickups — health, armour, ammunition, weapons, keys, the backpack and the power-ups, with Doom's messages and screen flashes
• the status bar, the automap, the intermission tallies, and the end-of-episode text
• sound effects from the WAD, placed and panned; the music played from the WAD's MUS lumps through TuningFork

What is not

• Doom II's monsters' own attacks (the arch-vile, revenant, mancubus, pain elemental and arachnotron do nothing when they attack) and Doom II's line specials above 104
• the music is General MIDI played by TuningFork's synthesised instruments, not the OPL sound of a Sound Blaster; reading the WAD's GENMIDI patches through an OPL emulator is the way to that sound
• saving and loading games, demos and deathmatch

How it is built

• ElixirDoom.Wad, Graphics and Level read the WAD: lumps, the composed wall textures, flats and patches as one Cauldron2D.Sectors.Pictures set, and each level as a Cauldron2D.Sectors.Map with the BSP the WAD carries
• ElixirDoom.Info is Doom's state table and thing definitions, generated from the GPL info.c by mix doom.info; states run through Cauldron2D.States, actions through ElixirDoom.Actions
• ElixirDoom.Game is the Cauldron2D.Game: a world (ElixirDoom.World) stepped 35 times a second — players (Player, Weapons), the level's machinery (Specials and the modules under it, run as Cauldron2D.Thinkers), then every thing (Mobj, Enemy, Combat, Items)
• ElixirDoom.Client is the Cauldron2D.Client.Game; its scene is a picture (ElixirDoom.Render, StatusBar, Text) that Cauldron's surface draws in whatever the terminal shows best

Speed

On E1M1, a whole picture with the status bar takes 0.6 ms at 160×100, 1.6 ms at 400×240 and 2.8 ms at 640×400. A tic — every player, machine and thing — takes 0.2 to 0.8 ms across the shareware levels. Reading the shareware WAD's pictures takes about a second, once.

Tests

mix test
DOOM_WAD=path/to/DOOM1.WAD mix test

Without DOOM_WAD the tests that play a level are skipped.

Licence

GPL-2.0-or-later. Doom's source was released by id Software under the GPL in 1999; the state table and thing definitions here are generated from it, and the rules follow it closely, so this package is a derivative of that source. Cauldron, which it plays on, is MIT and contains no Doom code or data.

The WADs are not covered by that release. Doom's pictures, sounds, music and levels are id Software's (now ZeniMax's), and this package only reads them from a WAD the player supplies.