StendhalScripting/Lua

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this page is a work-in progress

Stendhal supports Lua scripting via the LuaJ library.

Lua scripts end in the .lua extension & are stored in the data/script directory.

Lua Basics

For more detailed information, see the Lua reference manual.

Comments

Lua uses double dashes (--) for single line comments & double dashes followed by double square brackets ([[) & closed with double square brackets (]]) for multi-line comments: 

-- a single line comment

--[[
a multi-line comment
]]

Variables

By default, Lua variables are set in global scope (meaning it is exposed to the entire Lua engine). To create a variable in local scope, the local keyword must be used: 

-- a global variable
var1 = "Hello world!"

-- a local variable
local var2 = "Hello world!"

Data Types

Some common data types in Lua are string, integer, boolean, & table. Type names do not need to be declared when setting variables.

Examples: 

-- string variable
local var1 = "Hello world!"

-- integer variable
local var2 = 11

-- boolean variable
local var3 = true

-- table variable
local var4 = {}

Strings

String Concatenation

String concatenation is simple, much like Java uses a plus operator (+) to join strings, Lua uses two periods (..).

Example: 

-- create a string variable
local var = "Hello"

-- append another string
var = var .. " world!"

print(var) -- prints "Hello world!"

Tables

A Lua table is a data type similar to a Java list or map. Tables can be indexed or use key=value pairs.

(IMPORTANT NOTE: Lua table indexes begin at 1, not 0)

Creating Tables

An empty table is initialized with a pair of curly braces ({}): 

local mytable = {}

You can add values to indexed tables at initialization or with the table.insert method: 

-- create a table with values
local mytable = {"foo"}

-- add value
table.insert(mytable, "bar")

To create a key=value table, any of the following methods can be used to add values: 

-- all of these do the same thing, that is, assigning "bar" to mytable.foo
local mytable {
	foo = "bar",
	["foo"] = "bar",
}
mytable.foo = "bar"
mytable["foo"] = "bar"

Accessing Table Values

Square brackets ([]) enclosing an index number are used to access values in indexed tables (remember that Lua table indexes start at "1" not "0"): 

local mytable = {"foo", "bar"}

print(mytable[1]) -- prints "foo"
print(mytable[2]) -- prints "bar"

In a key=value table, values can be accessed by either enclosing the key string in square brackets or concatenating the key member using a .: 

local mytable = {foo="bar"}

-- using square brackets
print(mytable["foo"]) -- prints "bar"

-- using concatenated member
print(mytable.foo) -- prints "bar"

Iterating Tables

Tables can be iterated in a for loop using the pairs or ipairs iterators. Loops are terminated with the end keyword: 

local mytable = {"foo", "bar"}

print("indexes:")
for idx in pairs(mytable) do
	print(idx)
end

print("\nvalues:")
for idx, value in pairs(mytable) do
	print(value)
end

Output: 

indexes:
1
2

values:
foo
bar

Using a key=value table: 

local mytable = {
	["foo"] = "hello",
	["bar"] = " world!",
}

print("keys:")
for key in pairs(mytable) do
	print(key)
end

print("\nvalues:")
for key, value in pairs(mytable) do
	print(value)
end

Output: 

keys:
foo
bar

values:
hello
 world!

See also: Lua Tables Tutorial

Functions

Like normal variables, functions can be declared as global or local & must be terminated with the end keyword.

There are two ways to define functions with the function keyword: 

local function myFunction()
	print("Hello world!")
end

or 

local myFunction = function()
	print("Hello world!")
end

Functions can also be members of a table: 

local myTable = {}
function myTable.myFunction()
	print("Hello world!")
end

or 

local myTable = {}
myTable.myFunction = function()
	print("Hello world!")
end

or 

local myTable = {
	myFunction = function()
		print("Hello world!")
	end,
}

-- execute with
myTable.myFunction()

Comparison Operators

Logical Operators
Operator Description Java Equivalent
and logical and &&
or logical or ||
not logical opposite !
Relational Operators
Operator Description Java Equivalent
< less than <
> greater than >
<= less than or equal to <=
>= greater than or equal to >=
== equal to ==
~= not equal to !=

Stendhal Application

Zones

Setting Zone

To set the zone to work with, use the game object: 

game:setZone("0_semos_city")

Create New Zone

It is recommended to create new zones in the XML configurations in data/conf/zones.

Currently creating new zones via Lua is not supported.

Add Zone Music

Music can be added to zones with the game:setMusic function. It supports the following arguments:

  • filename: Basename of the OGG audio file to use stored in data/music.
  • args: A table of key=value integers.
  • Valid keys:
    • volume: Volume level (default: 100).
    • x: The horizontal point for the source of the music (default: 1).
    • y: The vertical point for the source of the music (default: 1).
    • radius: The radial range at which the music can be heard (default: 10000).

Example: 

if game:setZone("0_semos_plains_n") then
	game:setMusic("pleasant_creek_loop", {volume=85, radius=100})
end

Adding Entities

Signs

Signs can be created with entities:createSign and entities:createShopSign: 

local zone = "0_semos_city"
if game:setZone(zone) then
	-- create the sign instance
	local sign = entities:createSign()
	sign:setEntityClass("signpost")
	sign:setPosition(12, 55)
	sign:setText("Meet Lua!")

	-- Add it to the world
	game:add(sign)
else
	logger:error("Could not set zone: " .. zone)
end

NPCs

Use the entities:createSpeakerNPC method to create an interactive NPC: 

local zone = "0_semos_city"
if game:setZone(zone) then
	-- Use helper object to create a new NPC
	local npc = entities:createSpeakerNPC("Lua")
	npc:setEntityClass("littlegirlnpc")
	npc:setPosition(10, 55)
	npc:setBaseSpeed(0.1)
	npc:setCollisionAction(CollisionAction.STOP)

	local nodes = {
		{10, 55},
		{11, 55},
		{11, 56},
		{10, 56},
	}

	npc:setPath(nodes)

	-- Dialogue
	npc:addJob("Actually, I am jobless.")
	npc:addGoodbye();

	-- Add to the world
	game:add(npc)
else
	logger:error("Could not set zone: " .. zone)
end

Adding Transitions

A simple example of adding a chat transition can be done without any special functionality: 

local frank = entities:createSpeakerNPC("Frank")
frank:add(ConversationStates.IDLE,
	ConversationPhrases.GREETING_MESSAGES,
	nil,
	ConversationStates.ATTENDING,
	"Hello.",
	nil)

This simply adds a response to saying "hello" & sets the NPC to attend to the player (equivalent of frank:addGreeting("Hello")).

For more complicated behavior, we need to use some helper methods. If we want to check a condition we use the conditions:create method. The first parameter is the string name of the ChatCondition we want to instantiate. The second parameter is a table that contains the values that should be passed to the ChatCondition constructor.

Example: 

frank:add(ConversationStates.IDLE,
	ConversationPhrases.GREETING_MESSAGES,
	conditions:create("PlayerHasItemWithHimCondition", {"money"}),
	ConversationStates.ATTENDING,
	"Hello.",
	nil)

In this scenario, the NPC will only respond if the player is carrying money.

A NotCondition instance can be created with the actions:notCondition method:

Example usage: 

local condition = conditions.notCondition(conditions:create("PlayerHasItemWithHimCondition", {"money"})

To add a ChatAction, we use the actions:create method. Its usage is identical to conditions:create.

Example: 

frank:add(ConversationStates.IDLE,
	ConversationPhrases.GREETING_MESSAGES,
	conditions:create("PlayerHasItemWithHimCondition", {"money"}),
	ConversationStates.ATTENDING,
	"Hello.",
	actions:create("NPCEmoteAction", {"looks greedily at your pouch of money.", false}))

Lua tables can be used to add multiple conditions or actions: 

frank:add(ConversationStates.IDLE,
	ConversationPhrases.GREETING_MESSAGES,
	{
		conditions:create("PlayerHasItemWithHimCondition", {"money"}),
		conditions:notCondition(conditions:create("NakedCondition")),
	},
	ConversationStates.ATTENDING,
	nil,
	{
		actions:create("SayTextAction", {"Hello."}),
		actions:create("NPCEmoteAction", {"looks greedily at your pouch of money.", false}),
	})

In this scenario, the NPC will respond if the player has money & is not naked.

Nested tables are supported as well: 

local conditions = {
	conditions:create("PlayerHasItemWithHimCondition", {"money"}),
	{
		conditions:notCondition(conditions:create("NakedCondition")),
	},
}

frank:add(ConversationStates.IDLE,
	ConversationPhrases.GREETING_MESSAGES,
	conditions,
	ConversationStates.ATTENDING,
	nil,
	{
		actions:create("SayTextAction", {"Hello."}),
		actions:create("NPCEmoteAction", {"looks greedily at your pouch of money.", false}),
	})

Adding Merchant Behavior

The merchants object is used for adding merchant behavior (buying/selling) to an NPC.

Example of adding seller behavior to an NPC: 

if game:setZone("0_semos_city") then
	local frank = entities.createSpeakerNPC("Frank")
	merchants:addSeller(frank, merchants.shops:get("shopname"), true)

	game:add(frank)
end

To create a custom shop list, you can use a Lua table (there are multiple ways to add elements to a Lua table):

Method 1: 

local priceList = {
	meat = 50,
	["ham"] = 70,
}

Method 2: 

local priceList = {}
priceList.meat = 50
priceList["ham"] = 70

The helper methods have special handling for underscore characters as well (the following are all the same): 

local priceList = {
	smoked_ham = 100,
	["smoked ham"] = 100,
}
priceList.smoked_ham = 100
priceList["smoked ham"] = 100

Then add the seller behavior using the custom list: 

merchants:addSeller(frank, priceList, true)

System Properties

Java's system properties are exposed to Lua with the properties object.

Examples: 

-- property state
if properties:enabled("stendhal.testserver") then
	print("Test server enabled")
	if properties:equals("stendhal.testserver", "junk") then
		print("Junk enabled")
	else
		print("Junk disabled")
	end
else
	print("Test server disabled")
end

-- property value
local prop = properties:getValue("stendhal.testserver")
if prop ~= nil then
	print("Test server enabled")
	if prop == "junk" then
		print("Junk enabled")
	else
		print("Junk disabled")
	end
else
	print("Test server disabled")
end

Misc

Typecasting

Lua does not support typecasting (as far as I know), but if the class you want to cast to has a copy constructor, achieving the same functionality is quite simple. 

-- "entities:getItem" returns an instance of Item
local bestiary = entities:getItem("bestiary")

-- in order to use the bestiary's "setOwner" method, we must convert it to an "OwnedItem" instance by calling its copy constructor
bestiary = luajava.newInstance("games.stendhal.server.entity.item.OwnedItem", bestiary)
bestiary:setOwner("Ted")

See Also

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