python - Pygame 矩形从左到右移动

Question

我用 pygame.rect 创建了一个敌人类，我试图将其在屏幕上从右向左移动，然后向右返回并在循环中重复该操作。到目前为止，在敌人更新中我只能从右向左移动，然后矩形就会停止。这是因为它不断更新导致代码无法工作吗？我不确定如何实现双向。

# Pygame template - skeleton for a new pygame project
import pygame
import random
import os

# set up asset folders
os.environ['SDL_VIDEO_CENTERED'] = '1'
game_folder = os.path.dirname(__file__)
img_folder = os.path.join(game_folder, 'img')

# Screen resolution and frames
WIDTH = 480
HEIGHT = 600
FPS = 60

# define colors
WHITE = (255, 255, 255)
BLACK = (0, 0, 0)
RED = (255, 0, 0)
GREEN = (0, 255, 0)
BLUE = (0, 0, 255)

# initialize pygame and create window
pygame.init()
pygame.mixer.init()
screen = pygame.display.set_mode((WIDTH, HEIGHT))
pygame.display.set_caption("Shmup!")
clock = pygame.time.Clock()

class Player(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.Surface((100, 40))
        self.image.fill(GREEN)
        self.rect = self.image.get_rect()
        self.rect.centerx = WIDTH / 2
        self.rect.bottom = HEIGHT - 10
        self.speedx = 0
        self.speedy = 0

    def update(self):
        self.speedx = 0
        self.speedy = 0
        keystate = pygame.key.get_pressed()
        if keystate[pygame.K_LEFT]:
            self.speedx = -8
        if keystate[pygame.K_RIGHT]:
            self.speedx = 8
        self.rect.x += self.speedx
        if keystate[pygame.K_UP]:
            self.speedy = -8
        if keystate[pygame.K_DOWN]:
            self.speedy = 8
        self.rect.y += self.speedy
        if self.rect.right > WIDTH:
            self.rect.right = WIDTH
        if self.rect.left < 0:
            self.rect.left = 0
        if self.rect.bottom > HEIGHT:
            self.rect.bottom = HEIGHT
        if self.rect.top < 100:
            self.rect.top = 100



class Enemies(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.Surface((50, 40))
        self.image.fill(BLACK)
        self.rect = self.image.get_rect()
        self.rect.x = WIDTH - 10
        self.rect.bottom = HEIGHT / 2
        self.speedx = 0

    def update(self):
        self.speedx = 0
        if self.rect.right > 0:
            self.speedx = 2  
        self.speedx = -self.speedx
        if self.rect.left < 0:
            self.speedx *= -1
        self.speedx = self.speedx

        self.rect.x += self.speedx


all_sprites = pygame.sprite.Group()
player = Player()
enemies = Enemies()
all_sprites.add(player)
all_sprites.add(enemies)

# Game Loop
running = True
while running:
    # keep loop running at the right speed
    clock.tick(FPS)
    # Process input (events)
    for event in pygame.event.get():
        # check for closing window
        if event.type == pygame.QUIT:
            running = False


    # Update
    all_sprites.update()

    #Draw / render
    screen.fill(BLUE)
    all_sprites.draw(screen)
    # *after* drawing everything
    pygame.display.flip()

pygame.quit()
quit()

Answer 1

不要让事情过于复杂化。在构造函数中初始化恒速:

class Enemies(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        # [...]
        self.speedx = 2

有两种情况你必须改变速度。
如果敌人在左边(self.rect.left <= 0)，那么移动方向必须改为向右，这意味着self.speedx必须是积极的。使用 abs(x) 使速度为正值(例如 self.speedx = abs(self.speedx) )。
如果敌人在右侧( self.rect.right >= WIDTH )，则必须将直接更改为左侧。因此速度必须为负(例如 self.speedx = -abs(self.speedx) )。

以下代码始终将敌人移动到正确的方向，即使敌人在窗外:

class Enemies(pygame.sprite.Sprite):

    # [...]

    def update(self):
        if self.rect.left <= 0:
            self.speedx = abs(self.speedx)
        elif self.rect.right >= WIDTH:
            self.speedx = -abs(self.speedx) 
        self.rect.x += self.speedx