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Guide to writing Lua scripts in Hedgewars.
Updated Sun, 12 Jan 2020 23:31:19 +0100 by Wuzzy

Lua guide

This is both a simplistic introduction to Lua scripting in Hedgewars and a guide for more advanced control over the game. With Lua scripting, one can define own missions (both in training and campaign menu), mission maps (like Knockball) and styles (like Highlander).

What is a Lua script

A Lua script is used to make the game behave different by giving the Hedgewars engine different commands. The script gets called by the engine on different events and the script tells the engine what to do. Lua is a programming language, and you must first learn some basics about the Lua programming language to get started. See to learn more.

Lua in Hedgewars

Version 0.9.13 of Hedgewars introduced the ability to use Lua scripts to modify Hedgewars behaviour for different maps. The till then used triggers (only appeared in training maps) were removed.

The use of Lua scripts has been extended since then.

Now, Lua scripts are used for:

  • Missions, one of three types:
    • Training: Easy missions which explain the game, like a tutorial
    • Challenge: Missions in which the goal is to reach a high score
    • Scenario: Missions with a pre-set goal, like collecting a crate or killing all enemies
  • Mission maps (e.g. TrophyRace)
  • Styles (e.g. Highlander, Balanced Random Weapon)
  • Campaigns

The basic structure

Dependent on what type of script you want to write the requirements are a bit different, but before we go into that we must first create the .lua file. The location of the file depends on the script type.

  • If you want to make a mission for singleplayer then you create a new .lua in one of three directories, depending on the type:
    • Training: Data/Missions/Training
    • Challenge: Data/Missions/Challenge
    • Scenario: Data/Missions/Scenario
  • If you want to make a mission for multi player (also called a “mission map”) you create a map and create a new file map.lua in the map's folder.
  • If you want to make a custom game style, create a new .lua file in Data/Scripts/Multiplayer .
  • Campaign missions go into Data/Missions/Campaign/<CAMPAIGN NAME> .

To get started, a .lua file should generally be structured like this: function onGameInit() end function onAmmoStoreInit() end function onGameStart() end function onGameTick() end function onGearAdd(gear) end function onGearDelete(gear) end

These are event handlers and are called on different events by the engine. Now lets look at the initiation events.

The initiation events

The two most important event handlers are onGameInit and onAmmoStoreInit . They are used instead of loading a game scheme and weapon scheme and in campaign missions or standalone missions onGameInit is also used to add teams and hogs.

First we have onGameInit . On this event we should add all game modifiers and team setup. If you are making a mission you only need to specify the things you want to change on this event, everything not changed will be set to default. The available game modifiers can be found here: LuaEvents#onGameInit()

An example of setting up Barrel Mayhem in a style: function onGameInit() GameFlags = gfRandomOrder + gfSharedAmmo TurnTime = 30000 CaseFreq = 0 MinesNum = 0 MinesTime = 0 Explosives = 40 end

If you are doing a training or campaign mission you should also set Seed , Map and Theme . But you must also add teams and hogs on this event. This is done by using AddTeam and AddHog . An example of adding one team with one hog (these functions may only be used here): AddTeam("Team", 0xFF0002, "Simple", "Island", "Default", "hedgewars") AddHog("Hedgehog", 0, 1, "NoHat") To be able to play you must add another team and hog that should have another team color (this team has 0xFF0002 ) or if you only want one team add the game flag gfOneClanMode . Look into LuaGameplay and LuaGears to see what the other parameters of AddTeam and AddHog are.

In onAmmoStoreInit you set what weapons is available in the game. For every weapon, run SetAmmo (see LuaGameplay). This is used to set both starting weapons and weapons found in crates.

Here is an example of the initiation of a training mission: function onGameInit() Seed = 0 GameFlags = gfMultiWeapon + gfOneClanMode TurnTime = 25000 CaseFreq = 0 MinesNum = 0 Explosives = 0 Delay = 0 Map = "Mushrooms" Theme = "Nature" AddTeam("Team", 0xFF00002, "Simple", "Island", "Default", "hedgewars") AddHog("Hedgehog", 0, 1, "NoHat") end function onAmmoStoreInit() SetAmmo(amShotgun, 9, 0, 0, 0) end

Gears everywhere

Mostly everything in Hedgewars are made out of gears: grenades, bazooka shells, and cakes just to name a few. But these are just the visible gears, the whip's effect and rising water are also gears. But for now we will focus on the more visible ones.

The hogs are gears, too and when you shoot with bazooka the bazooka shell will be created and explode when it hits the ground. When the shell is created the onGearAdd event is called and the gear parameter will be the bazooka. And when it hits the ground, before the gear has been deleted, onGearDelete is invoked with the shell as parameter, after that it is removed.

Each gear has a gear type, for instance, a bazooka shell has the gear type of gtShell , a grenade has a gear type of gtGrenade , and so on. You will almost always need to check for the gear type with GetGearType in the onGearAdd function in order to do anything meaningful.

Gears also have a lot of various values to track their position, state, etc. These can be accessed and written to with several “getter” and “setter” functions like GetPos , GetHealth , SetTag , etc. See LuaGears for a full list. In Hedgewars, the gear values and some variable names do not always really mean what they seem to be, their concrete meaning often depends on the actual gear type. For instance, using GetHealth(h) on a hedgehog gear (gear type: gtHedgehog ) will return its health (obviously). Less obviously, using GetHealth on a flying saucer gear (gear type: gtJetpack ) will return its amount of fuel.

To learn all the gory detaily about gears, see GearTypes.

Other important event handlers

The last important event handlers are onGameTick and onGameTick20 . onGameTick is called every game tick, that is every millisecond which is a thousand times a second. onGameTick20 is called every 20 game ticks, that is, every 20 milliseconds.

These functions are very important for specifying actions which need to happen regularily. It is important to know when to use onGameTick , and when to use onGameTick20 . You can usually get away with just using onGameTick but must make sure any code inserted here must be efficient and fast, as this function is called very often. Complex code which takes more time to execute should go into onGameTick20 instead.

If you need a different interval other than 1 or 20 milliseconds, you can use modulo on the GameTicks variable which holds the total number of game ticks since the beginning of the game.

Getting started … for real

This was just a simplistic introduction which didn't cover everything.

A good way to learn Lua scripting in Hedgewars is to read existing scripts. We recommend to take a look into Data/Missions/Training/Basic_Training_-_Sniper_Rifle.lua which is the Lua script for the Sniper Rifle target practice training mission. It should give you a rough “feeling” of how a script is supposed to look and is heavily commented.

Continue with the following pages to learn more:

  • LuaAPI is the central landing page for everything about the Lua API
  • Missions for a more in-depth guide on how to create missions
  • LuaLibraries contains information about “libraries”, that is, extra scripts you can include for even more functions. One common library is Locale for making a mission translatable
  • GearTypes contains the list of all gear types, along with an explanation of how the gears and their values work