这是一个运行示例。请注意注释中的解释：

import pygame, random
import sys

WHITE = (255, 255, 255)
GREEN = (20, 255, 140)
GREY = (210, 210 ,210)
RED = (255, 0, 0)
PURPLE = (255, 0, 255)

SCREENWIDTH=1000
SCREENHEIGHT=578  


class Background(pygame.sprite.Sprite):
    def __init__(self, image_file, location, *groups):
        # we set a _layer attribute before adding this sprite to the sprite groups
        # we want the background to be actually in the back
        self._layer = -1
        pygame.sprite.Sprite.__init__(self, groups)
        # let's resize the background image now and only once
        # always call convert() (or convert_alpha) after loading an image
        # so the surface will have to correct pixel format
        self.image = pygame.transform.scale(pygame.image.load(image_file).convert(), (SCREENWIDTH, SCREENHEIGHT))
        self.rect = self.image.get_rect(topleft=location)

# we do everthing with sprites now, because that will make our live easier
class GeoFence(pygame.sprite.Sprite):
    def __init__(self, rect, *groups):
        # we set a _layer attribute before adding this sprite to the sprite groups
        self._layer = 0
        pygame.sprite.Sprite.__init__(self, groups)
        self.image = pygame.surface.Surface((rect.width, rect.height))
        self.image.fill(GREEN)
        self.rect = rect

class Worker(pygame.sprite.Sprite):
    def __init__(self, image_file, location, *groups):
        # we set a _layer attribute before adding this sprite to the sprite groups
        # we want the workers on top
        self._layer = 1
        pygame.sprite.Sprite.__init__(self, groups)
        self.image = pygame.transform.scale(pygame.image.load(image_file).convert_alpha(), (40, 40))
        self.rect = self.image.get_rect(topleft=location)
        # let's call this handy function to set a random direction for the worker
        self.change_direction()
        # speed is also random
        self.speed = random.randint(2, 4)

    def change_direction(self):
        # let's create a random vector as direction, so we can move in every direction
        self.direction = pygame.math.Vector2(random.randint(-100, 100), random.randint(-100, 100))

        # we don't want a vector of length 0, because we want to actually move
        # it's not enough to account for rounding errors, but let's ignore that for now
        while self.direction.length() == 0:
            self.direction = pygame.math.Vector2(random.randint(-100, 100), random.randint(-100, 100)) 

        # always normalize the vector, so we always move at a constant speed at all directions
        self.direction = self.direction.normalize()

    def update(self, screen):
        # there is a less than 1% chance every time that direction is changed
        if random.uniform(0,1)<0.005:
            self.change_direction()

        # now let's multiply our direction with our speed and move the rect
        vec = [int(v) for v in self.direction * self.speed]
        self.rect.move_ip(*vec)

        # if we're going outside the screen, move back and change direction
        if not screen.get_rect().contains(self.rect):
            self.change_direction()
        self.rect.clamp_ip(screen.get_rect())

pygame.init()

# currently, one group would be enough
# but if you want to use some collision handling in the future
# it's best to group all sprites into special groups (no pun intended)
all_sprites = pygame.sprite.LayeredUpdates()
workers = pygame.sprite.Group()
fences = pygame.sprite.Group()

screen = pygame.display.set_mode((SCREENWIDTH, SCREENHEIGHT))
pygame.display.set_caption("TEST")

# create multiple workers
for pos in ((0,0), (100, 100), (200, 100)):
    Worker("worker.png", pos, all_sprites, workers)

# create multiple of these green thingies
for rect in (pygame.Rect(510,150,75,52), pygame.Rect(450,250,68,40)):
    GeoFence(rect, all_sprites, fences)

# and the background
Background("background.jpg", [0,0], all_sprites)

carryOn = True
clock = pygame.time.Clock()

while carryOn:
    for event in pygame.event.get():
        if event.type==pygame.QUIT:
            carryOn = False

    # see how clean our main loop is
    # just calling update and draw on the all_sprites group
    all_sprites.update(screen)
    all_sprites.draw(screen)

    pygame.display.flip()

    clock.tick(20)