问题
I'm having problems understanding a game scene manager (FSM) in pygame that I try to replicate from this website: https://nicolasivanhoe.wordpress.com/2014/03/10/game-scene-manager-in-python-pygame/
I'll copy the code:
# -*- encoding: utf-8 -*-
# Modules
import pygame, sys
class Director:
"""Represents the main object of the game.
The Director object keeps the game on, and takes care of updating it,
drawing it and propagate events.
This object must be used with Scene objects that are defined later."""
def __init__(self):
self.screen = pygame.display.set_mode((640, 480))
pygame.display.set_caption("Game Name")
self.scene = None
self.quit_flag = False
self.clock = pygame.time.Clock()
def loop(self):
"Main game loop."
while not self.quit_flag:
time = self.clock.tick(60)
# Exit events
for event in pygame.event.get():
if event.type == pygame.QUIT:
self.quit()
if event.type == pygame.KEYDOWN:
if event.key == pygame.K_ESCAPE:
self.quit()
# Detect events
self.scene.on_event()
# Update scene
self.scene.on_update()
# Draw the screen
self.scene.on_draw(self.screen)
pygame.display.flip()
def change_scene(self, scene):
"Changes the current scene."
self.scene = scene
def quit(self):
self.quit_flag = True
class Scene:
"""Represents a scene of the game.
Scenes must be created inheriting this class attributes
in order to be used afterwards as menus, introduction screens,
etc."""
def __init__(self, director):
self.director = director
def on_update(self):
"Called from the director and defined on the subclass."
raise NotImplementedError("on_update abstract method must be defined in subclass.")
def on_event(self, event):
"Called when a specific event is detected in the loop."
raise NotImplementedError("on_event abstract method must be defined in subclass.")
def on_draw(self, screen):
"Se llama cuando se quiere dibujar la pantalla."
raise NotImplementedError("on_draw abstract method must be defined in subclass.")
class SceneHome(Scene):
""" Welcome screen of the game, the first one to be loaded."""
def __init__(self, director):
Scene.__init__(self, director)
def on_update(self):
pass
def on_event(self):
pass
def on_draw(self):
pass
def main():
dir = Director()
scene = SceneHome(dir)
dir.change_scene(scene)
dir.loop()
if __name__ == '__main__':
pygame.init()
main()
In the main function a director object and a scenehome object are instantiated. I understand that. Then it calls the method change_scene and passes the scenehome object. But I can't understand why a director object is a parameter inside the SceneHome class. It seems it does nothing. It looks to me as a circular call, but I don't know what it does. Why does it need a director inside the Scene class?
回答1:
The Director class is acting as your main game loop while letting the scenes handle all the logic within their own event and update methods. Which means to change scenes from a scene class to another, you'd need a reference to the director object to call self.director.change_scene(new_scene).
来源：https://stackoverflow.com/questions/42226099/why-does-a-scene-take-a-scene-manager-as-a-parameter