finita

Finite State Machine implementation for Lua. Based on Mat Buckland's Game AI by Example

Usage

Put fsm.lua inside your project and require it:

local FSM = require "fsm"

Finita uses the state class. Each state can be declared in separate file like this:

local MyMegaState = {}

function MyMegaState:new()
  local obj = {}
  setmetatable(obj, self)
  self.__index = self
  return obj
end

-- this method execute when the state is entered
function MyMegaState:enter(owner)
  -- do staff...
end

-- this is called by the FSM's update function each update step
function MyMegaState:execute(owner, ...)
  -- do staff...
end

-- this will execute when the state is exited
function MyMegaState:exit(owner)
  -- do staff...
end

return MyMegaState

Finita automatically checks that the state implements required methods. If state failed verification, FSM raise incorrect state declaration error

Example

local FSM = require "fsm"

local MenuState = require "menu_state"
local GameplayState = require "game_state"


local Game = {}

function Game:new()
  -- create instance of FSM class and pass Game as FSM owner
  self.fsm = FSM(self)

  -- owner stores links to all states
  self.states = {
	menu = MenuState:new(),
	gameplay = GameplayState:new()
  }

  -- set current state
  self.fsm:set_current_state(self.states.menu)

  local obj = {}
  setmetatable(obj, self)
  self.__index = self
  return obj
end

function Game:update(dt)
  -- update fsm and pass extra paremeter 'dt' to current_state execute method
  self.fsm:update(dt)
end

function Game:handle_input(key)
  if key == "Enter" then
    -- change current state
    self.fsm:change_state(self.states.gameplay)
  end
end

return Game

Documentation

FSM(owner)

create new FSM object:

local  fsm = FSM(owner)

---

:set_owner(owner)

passed owner of FSM. If owner is nil method raise try to set nil owner error

---

Methods for initialize FSM:

:set_current_state(state)

:set_previous_state(state)

:set_global_state(state)

set_current_state() and set_global_state() calls enter methods of passed state.

---

:update(...) call this method to update FSM. You can pass variable numbers of arguments to update. Method executes the following sequence:

• if global state exist, call its execute method
• same for the current state

---

:change_state(new_state) method executes the following sequence:

• call the exit method of the existing state
• change current state to the new state
• call the enter method of the new state

This method can raise two errors:

• current_state was nil if current sate not passed in FSM
• trying to change to invalid state if new state failed verification

---

:revent_to_previous_state()

change state back to the previous state

---

:is_in_state(state)

returns true if the current state is equal to the state passed as a parameter

Testing

Tests defined with busted test farmework. To run the suite, install busted and simply execute busted in the module directory.