Difference between revisions of "LuaAPI"

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== See Also ==
 
== See Also ==
 
* [[LuaAPI/UpdatingFrom14]]
 
* [[LuaAPI/UpdatingFrom14]]
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* [[LuaAPI/old]] - The reference for the 1.14 Lua API, which may be useful if porting older add-ons
  
 
[[Category:Lua Reference|*]]
 
[[Category:Lua Reference|*]]

Revision as of 18:12, 1 July 2023

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 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.

See Also

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