# 有限状态机

http://eyehere.net/2011/python-pygame-novice-professional-index/

FSM(Finite-state machine)的严格定义，需要state和action和转移函数都是确定性的，也就是说，必须要在完全把握所有交互可能性的时候，限定一个有限的交互状态、交互动作和转移函数。

``````class State(object):
def __init__(self, name):
self.name = name
def do_actions(self):
pass

def check_conditions(self):
pass

def entry_actions(self):
pass

def exit_actions(self):
pass

class StateMachine(object):
def __init__(self):
self.states = {}
self.active_state = None

self.states[state.name] = state

if self.active_state is None:
return
self.active_state.do_actions()
new_state_name = self.active_state.check_conditions()
if new_state_name is not None:
self.set_state(new_state_name)

def set_state(self, new_state_name):
if self.active_state is not None:
self.active_state.exit_actions()
self.active_state = self.states[new_state_name]
self.active_state.entry_actions()

``````

``````SCREEN_SIZE = (640, 480)
NEST_POSITION = (320, 240)
ANT_COUNT = 20
NEST_SIZE = 100.

import pygame
from pygame.locals import *

from random import randint, choice
from gameobjects.vector2 import Vector2

class State(object):
def __init__(self, name):
self.name = name
def do_actions(self):
pass
def check_conditions(self):
pass
def entry_actions(self):
pass
def exit_actions(self):
pass

class StateMachine(object):
def __init__(self):
self.states = {}
self.active_state = None

self.states[state.name] = state

def think(self):
if self.active_state is None:
return
self.active_state.do_actions()
new_state_name = self.active_state.check_conditions()
if new_state_name is not None:
self.set_state(new_state_name)

def set_state(self, new_state_name):
if self.active_state is not None:
self.active_state.exit_actions()
self.active_state = self.states[new_state_name]
self.active_state.entry_actions()

class World(object):
def __init__(self):
self.entities = {}
self.entity_id = 0
self.background = pygame.surface.Surface(SCREEN_SIZE).convert()
self.background.fill((255, 255, 255))
pygame.draw.circle(self.background, (200, 255, 200), NEST_POSITION, int(NEST_SIZE))

self.entities[self.entity_id] = entity
entity.id = self.entity_id
self.entity_id += 1

def remove_entity(self, entity):
del self.entities[entity.id]

def get(self, entity_id):
if entity_id in self.entities:
return self.entities[entity_id]
else:
return None

def process(self, time_passed):
time_passed_seconds = time_passed / 1000.0
for entity in self.entities.values():
entity.process(time_passed_seconds)

def render(self, surface):
surface.blit(self.background, (0, 0))
for entity in self.entities.itervalues():
entity.render(surface)

def get_close_entity(self, name, location, range=100.):
location = Vector2(*location)
for entity in self.entities.itervalues():
if entity.name == name:
distance = location.get_distance_to(entity.location)
if distance < range:
return entity
return None

class GameEntity(object):

def __init__(self, world, name, image):

self.world = world
self.name = name
self.image = image
self.location = Vector2(0, 0)
self.destination = Vector2(0, 0)
self.speed = 0.
self.brain = StateMachine()
self.id = 0

def render(self, surface):
x, y = self.location
w, h = self.image.get_size()
surface.blit(self.image, (x-w/2, y-h/2))

def process(self, time_passed):
self.brain.think()
if self.speed > 0. and self.location != self.destination:
vec_to_destination = self.destination - self.location
distance_to_destination = vec_to_destination.get_length()
travel_distance = min(distance_to_destination, time_passed * self.speed)

class Leaf(GameEntity):
def __init__(self, world, image):
GameEntity.__init__(self, world, "leaf", image)

class Spider(GameEntity):
def __init__(self, world, image):
GameEntity.__init__(self, world, "spider", image)
self.health = 25
self.speed = 50. + randint(-20, 20)

def bitten(self):
self.health -= 1
if self.health <= 0:
self.speed = 0.
self.speed = 140.

def render(self, surface):
GameEntity.render(self, surface)
x, y = self.location
w, h = self.image.get_size()
bar_x = x - 12
bar_y = y + h/2
surface.fill( (255, 0, 0), (bar_x, bar_y, 25, 4))
surface.fill( (0, 255, 0), (bar_x, bar_y, self.health, 4))

def process(self, time_passed):
x, y = self.location
if x > SCREEN_SIZE[0] + 2:
self.world.remove_entity(self)
return
GameEntity.process(self, time_passed)

class Ant(GameEntity):
def __init__(self, world, image):
GameEntity.__init__(self, world, "ant", image)
exploring_state = AntStateExploring(self)
seeking_state = AntStateSeeking(self)
delivering_state = AntStateDelivering(self)
hunting_state = AntStateHunting(self)
self.carry_image = None

def carry(self, image):
self.carry_image = image

def drop(self, surface):
if self.carry_image:
x, y = self.location
w, h = self.carry_image.get_size()
surface.blit(self.carry_image, (x-w, y-h/2))
self.carry_image = None

def render(self, surface):
GameEntity.render(self, surface)
if self.carry_image:
x, y = self.location
w, h = self.carry_image.get_size()
surface.blit(self.carry_image, (x-w, y-h/2))

class AntStateExploring(State):
def __init__(self, ant):
State.__init__(self, "exploring")
self.ant = ant

def random_destination(self):
w, h = SCREEN_SIZE
self.ant.destination = Vector2(randint(0, w), randint(0, h))

def do_actions(self):
if randint(1, 20) == 1:
self.random_destination()

def check_conditions(self):
leaf = self.ant.world.get_close_entity("leaf", self.ant.location)
if leaf is not None:
self.ant.leaf_id = leaf.id
return "seeking"
spider = self.ant.world.get_close_entity("spider", NEST_POSITION, NEST_SIZE)
if spider is not None:
if self.ant.location.get_distance_to(spider.location) < 100.:
self.ant.spider_id = spider.id
return "hunting"
return None

def entry_actions(self):
self.ant.speed = 120. + randint(-30, 30)
self.random_destination()

class AntStateSeeking(State):
def __init__(self, ant):
State.__init__(self, "seeking")
self.ant = ant
self.leaf_id = None

def check_conditions(self):
leaf = self.ant.world.get(self.ant.leaf_id)
if leaf is None:
return "exploring"
if self.ant.location.get_distance_to(leaf.location) < 5.0:
self.ant.carry(leaf.image)
self.ant.world.remove_entity(leaf)
return "delivering"
return None

def entry_actions(self):
leaf = self.ant.world.get(self.ant.leaf_id)
if leaf is not None:
self.ant.destination = leaf.location
self.ant.speed = 160. + randint(-20, 20)

class AntStateDelivering(State):
def __init__(self, ant):
State.__init__(self, "delivering")
self.ant = ant

def check_conditions(self):
if Vector2(*NEST_POSITION).get_distance_to(self.ant.location) < NEST_SIZE:
if (randint(1, 10) == 1):
self.ant.drop(self.ant.world.background)
return "exploring"
return None

def entry_actions(self):
self.ant.speed = 60.
random_offset = Vector2(randint(-20, 20), randint(-20, 20))
self.ant.destination = Vector2(*NEST_POSITION) + random_offset

class AntStateHunting(State):
def __init__(self, ant):
State.__init__(self, "hunting")
self.ant = ant
self.got_kill = False

def do_actions(self):
spider = self.ant.world.get(self.ant.spider_id)
if spider is None:
return
self.ant.destination = spider.location
if self.ant.location.get_distance_to(spider.location) < 15.:
if randint(1, 5) == 1:
spider.bitten()
if spider.health <= 0:
self.ant.carry(spider.image)
self.ant.world.remove_entity(spider)
self.got_kill = True

def check_conditions(self):
if self.got_kill:
return "delivering"
spider = self.ant.world.get(self.ant.spider_id)
if spider is None:
return "exploring"
if spider.location.get_distance_to(NEST_POSITION) > NEST_SIZE * 3:
return "exploring"
return None

def entry_actions(self):
self.speed = 160. + randint(0, 50)

def exit_actions(self):
self.got_kill = False

def run():
pygame.init()
screen = pygame.display.set_mode(SCREEN_SIZE, 0, 32)
world = World()
w, h = SCREEN_SIZE
clock = pygame.time.Clock()

for ant_no in xrange(ANT_COUNT):
ant = Ant(world, ant_image)
ant.location = Vector2(randint(0, w), randint(0, h))
ant.brain.set_state("exploring")

while True:
for event in pygame.event.get():
if event.type == QUIT:
return
time_passed = clock.tick(30)

if randint(1, 10) == 1:
leaf = Leaf(world, leaf_image)
leaf.location = Vector2(randint(0, w), randint(0, h))

if randint(1, 100) == 1:
spider = Spider(world, spider_image)
spider.location = Vector2(-50, randint(0, h))
spider.destination = Vector2(w+50, randint(0, h))