三条命

本课属于 Coddy Pygame 学习旅程的“精灵与图像”单元。第 36 课，共 39 课。

现在敌人可以伤害你了。飞船有 3 条命。敌人越过底部时会扣 1 条命，撞上飞船时也会扣 1 条命：

crashes = pygame.sprite.spritecollide(player, enemies, True, pygame.sprite.collide_mask)
for enemy in crashes:
    lives -= 1
    explosions.add(Explosion(enemy.rect.center))

飞船也需要一个 self.mask，供 collide_mask 使用。在消灭越过底部的敌人的循环中，也要扣 1 条命。

两个敌人可能在同一帧内扣掉最后两条命，让 lives 变成 -1。显示 max(lives, 0)，也就是两个数字中较大的那个，这样计数器就不会显示低于 0 的数。文本的 get_rect(topright=(x, y)) 会将文本定位在右上角，因此无论文本有多宽，它都会贴着右边缘。

挑战

中等

让敌人消耗生命值。

在循环之前设置 lives = 3，并为 Player 添加 self.mask。
在击杀越过底部的敌人的地方，也扣除一条生命。
spritecollide(player, enemies, True, pygame.sprite.collide_mask) 中的每个敌人都会消耗一条生命并爆炸。
绘制 f"Lives: {max(lives, 0)}"，并将其右上角放在 (630, 10)。

按下“开始”，让一个敌人通过：画面会显示 Lives: 2。然后点击“检查”。

亲手试试

import random
import pygame

pygame.init()
screen = pygame.display.set_mode((640, 480))
pygame.display.set_caption("Star Patrol")
clock = pygame.time.Clock()
font = pygame.font.Font(None, 32)

ship_image = pygame.image.load("assets/images/ship.png").convert_alpha()
laser_image = pygame.image.load("assets/images/laser.png").convert_alpha()
red_image = pygame.image.load("assets/images/enemy_red.png").convert_alpha()
explosion_frames = []
for number in range(1, 5):
    explosion_frames.append(pygame.image.load(f"assets/images/explosion_{number}.png").convert_alpha())


class Player(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        self.image = ship_image
        self.rect = self.image.get_rect(midbottom=(320, 470))

    def update(self):
        keys = pygame.key.get_pressed()
        if keys[pygame.K_LEFT]:
            self.rect.x -= 6
        if keys[pygame.K_RIGHT]:
            self.rect.x += 6
        self.rect.clamp_ip(screen.get_rect())


class Laser(pygame.sprite.Sprite):
    def __init__(self, x, y):
        super().__init__()
        self.image = laser_image
        self.rect = self.image.get_rect(midbottom=(x, y))
        self.mask = pygame.mask.from_surface(self.image)

    def update(self):
        self.rect.y -= 10
        if self.rect.bottom < 0:
            self.kill()


class Enemy(pygame.sprite.Sprite):
    def __init__(self, image, x, y, speed):
        super().__init__()
        self.image = image
        self.rect = self.image.get_rect(center=(x, y))
        self.mask = pygame.mask.from_surface(self.image)
        self.speed = speed

    def update(self):
        self.rect.y += self.speed


class Explosion(pygame.sprite.Sprite):
    def __init__(self, center):
        super().__init__()
        self.index = 0
        self.timer = 0
        self.image = explosion_frames[0]
        self.rect = self.image.get_rect(center=center)

    def update(self):
        self.timer += 1
        if self.timer == 5:
            self.timer = 0
            self.index += 1
            if self.index == len(explosion_frames):
                self.kill()
            else:
                self.image = explosion_frames[self.index]


def spawn_wave(image, count, speed):
    for i in range(count):
        x = random.randint(40, 600)
        enemies.add(Enemy(image, x, -40 - i * 120, speed))


player = Player()
lasers = pygame.sprite.Group()
enemies = pygame.sprite.Group()
explosions = pygame.sprite.Group()
last_shot = 0
score = 0
spawn_wave(red_image, 6, 2)

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

    player.update()
    keys = pygame.key.get_pressed()
    now = pygame.time.get_ticks()
    if keys[pygame.K_SPACE] and now - last_shot >= 250:
        lasers.add(Laser(player.rect.centerx, player.rect.top))
        last_shot = now
    lasers.update()
    enemies.update()
    for enemy in enemies:
        if enemy.rect.top > 480:
            enemy.kill()
    hits = pygame.sprite.groupcollide(enemies, lasers, True, True, pygame.sprite.collide_mask)
    for enemy in hits:
        score += 10
        explosions.add(Explosion(enemy.rect.center))
    explosions.update()

    screen.fill((12, 14, 30))
    enemies.draw(screen)
    lasers.draw(screen)
    screen.blit(player.image, player.rect)
    explosions.draw(screen)
    score_text = font.render(f"Score: {score}", True, (240, 240, 240))
    screen.blit(score_text, (10, 10))
    pygame.display.flip()
    clock.tick(60)

pygame.quit()