LuaAPI

All Lua API functionality is available in one of several global module tables, as well as some global functions which form the basic Lua API. Wesnoth uses Lua 5.4 which is documented in detail on the Lua website.

This page documents the modules, functions, and other APIs available for use when writing Lua for Wesnoth. For information on how to tell the engine about your Lua code, see LuaWML.

Conventions used in this manual

On this page and any page linked from it, variable values will be shown in italic type, while literal names will be shown in bold type. Variable values may be parameters, self values, indexes, or field names on a table. Return values will be indicated by a right arrow (→) followed by a list of names in italics. The arrow will be omitted for a function that returns nothing. Optional portions will be enclosed in square brackets. The commas for optional parameters will not be included in the brackets, even though they must be omitted if the optional parameter is omitted.

Functions

For example, the following line would be seen in the documentation of a function that returns two values and has an optional parameter:

wesnoth.some_function(some_parameter, [some_optional_parameter]) → first_return_value, second_return_value

Methods

The following example documents a function that can be called as a method on a some_value, taking one additional parameter and returning one value.

some_value:some_method(some_parameter) → some_new_value

Variadic Functions

Functions that take a variable number of parameters or return a variable number of values where the specific meaning of the parameters is unspecified will use the string "..." to indicate this. For example:

wesnoth.variadic_function(required_param, [...])
wesnoth.get_several_values(param) → ...

The first of these takes a variable number of parameters, but requires at least one parameter. The second takes one parameter and returns a variable number of values.

Member Variables

Not all documented APIs are functions. When documenting userdata types, as well as some complex tables returned by API functions, the following syntax is used for member variables. The right arrow may be replaced with a left arrow (←) if it is write-only, or a double-ended arrow (↔) if it is read-write. Read-only members may return multiple values. The following examples document a read-write member, a read-only member that returns two values, and a write-only member respectively.

some_value.some_member ↔ result
some_value.read_only_member → first_result, second_result
some_value.write_only_member ← input

Operators

Custom types in Lua can overload operators with new functionality. Some examples of how these would be documented:

#wesnoth.list_like_object → number of somethings
wesnoth.list_like_object[index] ↔ a something definition table
comparable_value == comparable_value → whether they are equal
operable_value + operable_value → result

The first example documents that you can get the length of that object. The same format would be used for other unary operators as well.

The second example documents that you can index the object with arbitrary values. Whether the index needs to be a number would usually be mentioned in the detailed description, although the placeholder name may also make it clear. This example could also use a single-directional arrow to indicate that it is read-only or write-only.

The third example documents that you can compare two values of that type with the equality operator, and the fourth example documents that you can add two values of that type together with the addition operator.

Iterators

For functions that return an iterator, a double arrow indicates the values yielded when you use the iterator in a for loop. The following example documents a function returning an iterator that yields three values.

wesnoth.some_function() → iterator ⇒ a, b, c

Hooks

Some parts of the API are so-called hooks, meaning that you define a function in a special location and it has some effect on the game. The following example documents a hook which takes one parameter and returns a value. Usually the double-ended arrow is used for hooks, but some may be write-only.

wesnoth.some_table.name ↔ function(parameter) → expected return value

Context Specifiers

Many functions and variables are only available in certain contexts. Currently, there are three possible contexts - plugins, map generators, and the game. Most Lua will run in the game kernel. If a function is only available in certain contexts, that will be indicated with an icon at the beginning of the definition. For example:

♟ wesnoth.game_exclusive_function(parameter) → result

The possible icons are:

♟ Available in the game context. Most Lua in Wesnoth runs in the game context, which is initialized when a game begins and destroyed upon victory or loss.
⌖ Available in the map generation context. This context is created at the game creation screen, generally to generate a map for a scenario.
🔌 Available in the plugins context. There is only one plugins context, which is initialized when Wesnoth launches and remains valid until it shuts down. A plugin is a Lua script loaded via the command-line option --plugin that runs as a coroutine in parallel with the game UI. It can automatically connect to a server and host or join a game. This API is documented at LuaPluginAPI.

Built-in Modules

The following built-in Lua modules are available:

basic — except dofile, require, and loadfile; also note that print redirects to the Lua console interface rather than standard output; you can use std_print if you need the default Lua behavior.
coroutine
string
utf8
table
math — note that math.random is unsafe for MP usage; wesnoth provides a separate MP-safe random function
os — only the clock, date, time, and difftime functions are available (but keep in mind that they are not MP safe)
debug — only the traceback function is available

Wesnoth Modules

Wesnoth also provides several modules of its own, some of which are loaded by default while others require you to load them as needed. Note: APIs named wesnoth.something, for example wesnoth.scenario, might be part of Core and not a separate module.

wesnoth (Core) - The wesnoth module contains most of the core Wesnoth API. It is always loaded and available.
- wesnoth.interface (Game Interface) - (Version 1.15.0 and later only) The interface submodule contains functions for querying or manipulating the in-game UI.
- wesnoth.units (Units) - (Version 1.15.0 and later only) The units submodule contains functions for manipulating units on the map or recall list.
- wesnoth.schedule (Schedule) - (Version 1.15.14 and later only) The schedule submodule contains functions for manipulating the time of day schedule in the scenario.
- wesnoth.sides (Sides) - (Version 1.15.3 and later only) The sides submodule contains functions for manipulating sides in the scenario.
- wesnoth.sync (Synchronization) - (Version 1.15.3 and later only) The sync submodule contains functions for keeping multiplayer games synchronized.
- wesnoth.map (Game Map) - (Version 1.15.11 and later only) The map submodule contains functions for querying and manipulating the game map.
- wesnoth.audio (Audio) - (Version 1.15.13 and later only) The audio submodule contains functions for playing music and sound effects.
- wesnoth.paths (Pathfinding) - (Version 1.15.14 and later only) The paths submodule contains functions related to pathfinding.
- wesnoth.game_events (Event Handling) - The game_events submodule contains functions and hooks related to event handling.
- wesnoth.achievements (Achievements Support) - (Version 1.17.13 and later only) The achievements submodule contains functions for checking and setting achievements.
gui (User Interface) - (Version 1.15.0 and later only) The gui module contains routines for showing dialogs on the screen. It does not contain anything for manipulating the in-game UI, however. See GUIToolkit for details of the UI toolkit.
- gui.widget (GUI Widget Support) - (Version 1.15.6 and later only) The widget submodule contains routines for operating on dialog widgets. Since they take a widget reference as an argument, they can only be called while a dialog is onscreen.
wml (WML Tables) - The wml module contains functions for working with WML tables.
location_set (Location Sets) - A module for working with sets of locations, optionally associating data to each location. Not loaded by default.
functional - Higher-order functions module. Not loaded by default.
stringx - Additional string support functions, to augment the built-in string module.
mathx - (Version 1.15.13 and later only) Additional math and randomization support functions, to augment the built-in math module.
filesystem - (Version 1.15.13 and later only) Functions that allow read-only access to arbitrary files in the data folder.
ai - Functions that instruct the AI on how to move.
wml-utils - Useful functions for implementing custom WML tags.
unit_test - Functions that can be used to write unit tests; only available in [test] scenarios.

Wesnoth Types

Wesnoth defines a large number of userdata types, some of which are quite common and complex. Most of them are documented alongside the function that creates them, but some of the most common or complex ones are listed below.

translatable strings - a string that will be translated by the engine.
vconfig - a WML object that automatically substitutes variables on the fly.
unit - represents a reference to Wesnoth unit on the map, on the recall list, or private to Lua.
weapon - represents a unit's weapon.
race - represents a unit's race.
unit type - represents a unit's type.
side - represents a single side (player) in the game.
widget - represents a GUI2 widget.
map - represents the game map.
hex - represents a single hex on the map.