StendhalScripting/Lua

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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

Be 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 = {}

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)

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:

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

mytable.foo = "bar"
mytable["foo"] = "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 declare functions:

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

or

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

Functions can also be values in 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

Objects and Functions

The following objects & functions are exposed to the Lua engine:

luajava

This is an object of the LuajavaLib library. It can be used to coerce Java static objects to Lua or create new Java object instances.

Example of exposing a static object & enums to Lua:

-- store a Java enum in a Lua global variable
ConversationStates = luajava.bindClass("games.stendhal.server.entity.npc.ConversationStates")

-- access the enum values like so
ConversationStates.IDLE

Example of creating an object instance:

-- store instance in local variable
local dog = luajava.newInstance("games.stendhal.server.entity.npc.SilentNPC")
-- access object methods like so
dog:setEntityClass("animal/puppy")
dog:setPosition(2, 5)

-- class with constructor using parameters
local speaker = luajava.newInstance("games.stendhal.server.entity.npc.SpeakerNPC", "Frank")
speaker:setOutfit("body=0,head=0,eyes=0,hair=5,dress=5")
speaker:setPosition(2, 6)

To make scripting easier, Stendhal employs a master script & some helper objects & methods to handle the functionality mentioned above. An explanation of these objects & methods follows.

game

The main object that handles setting zone & adding entities to game.

Methods:

• game:add(object) - Adds an object to the current zone.
• game:setZone(name) - Sets the current zone.
• game:createSign(visible) - Creates a new Sign instance.
• game:createShopSign(name, title, caption, seller) - Creates a new ShopSign instance.

npcHelper

This object helps to create instances of SpeakerNPC & SilentNPC classes.

Methods:

• npcHelper:createSpeakerNPC(name) - Creates a new SpeakerNPC.
• npcHelper:createSilentNPC() - Creates a new SilentNPC.
• npcHelper:setPath(npc, path, loop) - Sets the path for the specified NPC.
• npcHelper:setPathAndPosition(npc, path, loop) - Sets the path & starting position of the specified NPC.
• npcHelper:addMerchant(merchantType, npc, items, offer) - Adds merchant behavior to npc of either a buyer or seller defined by merchantType.
• npcHelper:addSeller(npc, items, offer) - Adds seller merchant behavior to npc.
• npcHelper:addBuyer(npc, items, offer) - Adds buyer merchant behavior to npc.

Zones

Setting Zone

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

game:setZone("0_semos_city")

The logger is exposed to Lua via the logger object:

local zone = "0_semos_city"
if game:setZone(zone) then
	-- do something
else
	logger:error("Could not set zone: " .. zone)
end

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 setZoneMusic global function. It supports the following arguments:

• filename: Basename of the OGG audio file to use stored in data/music.
• volume: (optional) Volume level.
• x: (optional) The horizontal point for the source of the music.
• y: (optional) The vertical point for the source of the music.
• radius: (optional) The radial range at which the music can be heard.

Example:

if game:setZone("0_semos_plains_n") then
	setZoneMusic("pleasant_creek_loop", 85)
end

Adding Entities

Signs

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

local zone = "0_semos_city"
if game:setZone(zone) then
	-- create the sign instance
	local sign = game: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 game: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 = npcHelper: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},
	}

	-- Use helper object to create NPC path
	npcHelper:setPath(npc, 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 = npcHelper: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.

For more complicated behavior, we need to use some helper methods. If we want to check a condition we use the newCondition global function:

frank:add(ConversationStates.IDLE,
	ConversationPhrases.GREETING_MESSAGES,
	newCondition("PlayerHasItemWithHimCondition", "money"),
	ConversationStates.ATTENDING,
	"Hello.",
	nil)

In this scenario, the NPC will only respond if the player is carrying <item>money</item>.

A NotCondition instance can be created with the newNotCondition global function:

newNotCondition(newCondition("PlayerHasItemWithHimCondition", "money"))

To add a ChatAction, we use the newAction global function:

frank:add(ConversationStates.IDLE,
	ConversationPhrases.GREETING_MESSAGES,
	newCondition("PlayerHasItemWithHimCondition", "money"),
	ConversationStates.ATTENDING,
	"Hello.",
	newAction("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,
	{
		newCondition("PlayerHasItemWithHimCondition", "money"),
		newNotCondition(newCondition("NakedCondition")),
	},
	ConversationStates.ATTENDING,
	nil,
	{
		newAction("SayTextAction", "Hello."),
		newAction("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 = {
	newCondition("PlayerHasItemWithHimCondition", "money"),
	{
		newNotCondition(newCondition("NakedCondition")),
	},
}

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

Adding Merchant Behavior

Merchant behavior (buying/selling) can be set with one of the following helper functions:

• npcHelper:addMerchant(merchantType, npc, prices, addOffer)
• npcHelper:addBuyer(npc, prices, addOffer)
• npcHelper:addSeller(npc, prices, addOffer)
  • Arguments:
    • merchantType: (string) If set to "buyer", will add buyer behavior, otherwise will be "seller" (may change type to boolean in future).
    • npc: (SpeakerNPC) The NPC to add the behavior to.
    • prices: (Map<String, Integer> or LuaTable) List of items & their prices.
    • addOffer: (boolean) If true, will add default replies for "offer".

Example of adding seller behavior to an NPC:

if game:setZone("0_semos_city") then
	local frank = npcHelper.createSpeakerNPC("Frank")
	npcHelper:addSeller(frank, 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:

npcHelper:addSeller(frank, priceList, true)