#summary Guide to writing Lua scripts in Hedgewars.

= 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), [PresetMaps 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 [http://www.lua.org/] 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
 * [PresetMaps Mission maps] (e.g. TrophyRace)
 * [GameStyles 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 [GearTypes 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