踩敌人，还是被击中

本课属于 Coddy Pygame 学习旅程的“游戏世界”单元。第 25 课，共 36 课。

碰到一个 blob 时，应该有两种不同的效果。从它上方落到它身上，就能打败它。撞上它，玩家就会受伤。

区别在于玩家是怎么到达那里的。如果玩家正在下落，也就是 vel_y > 0，并且脚还在 blob 中间位置的上方：

for blob in blobs:
    if player.colliderect(blob.rect):
        if vel_y > 0 and player.bottom < blob.rect.centery:
            blob.kill()
            vel_y = -8
        else:
            player.midbottom = start
            vel_y = 0

blob.kill() 会将精灵从组中移除，因此它不再更新或绘制。vel_y = -8 会让玩家稍微弹起，表示踩踏成功，还可以接着跳跃。其他情况都表示从侧面或下方撞上了它，玩家会回到起点，就像跌落之后一样。

遍历这个组，逐个检测 blob。在循环中调用 kill() 在这里是安全的，因为循环会遍历开始时组中的精灵。

挑战

中等

让玩家踩扁 Blob，否则就会被它们伤到。

在 Blob 移动后，遍历 blobs。
接触时：如果 vel_y > 0 且 player.bottom < blob.rect.centery，调用 blob.kill() 并设置 vel_y = -8。
否则，设置 player.midbottom = start 和 vel_y = 0。

按“运行”，然后跳到 Blob 上：它会消失，你会弹起来。接着按“检查”。

亲手试试

import pygame

TILE = 36
SPEED = 4
GRAVITY = 1
JUMP = -15
MAX_FALL = 12

LEVEL = [
    "................",
    "................",
    "................",
    "................",
    "..........####..",
    "................",
    "...####.........",
    "................",
    "#.P............#",
    "################",
]

pygame.init()
screen = pygame.display.set_mode((576, 360))
pygame.display.set_caption("Stomp")
clock = pygame.time.Clock()

background = pygame.image.load("assets/backgrounds/clouds.png").convert_alpha()
block_img = pygame.image.load("assets/images/block.png").convert_alpha()
player_img = pygame.image.load("assets/images/player.png").convert_alpha()
blob_img = pygame.image.load("assets/images/blob.png").convert_alpha()


class Blob(pygame.sprite.Sprite):
    def __init__(self, midbottom):
        super().__init__()
        self.image = blob_img
        self.rect = pygame.Rect(0, 0, 30, 26)
        self.rect.midbottom = midbottom
        self.direction = 1

    def update(self):
        self.rect.x += self.direction
        if self.direction > 0:
            ahead = self.rect.right
        else:
            ahead = self.rect.left - 1
        hit_wall = any(self.rect.colliderect(wall) for wall in walls)
        ground_ahead = any(wall.collidepoint(ahead, self.rect.bottom) for wall in walls)
        if hit_wall or not ground_ahead:
            self.rect.x -= self.direction
            self.direction = -self.direction

walls = []
for row, line in enumerate(LEVEL):
    for col, char in enumerate(line):
        if char == "#":
            walls.append(pygame.Rect(col * TILE, row * TILE, TILE, TILE))
        elif char == "P":
            start = (col * TILE + TILE // 2, row * TILE + TILE)

blobs = pygame.sprite.Group(Blob((432, 144)), Blob((432, 324)))
player = player_img.get_rect(midbottom=start)
vel_y = 0
on_ground = False

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        elif event.type == pygame.KEYDOWN and event.key in (pygame.K_SPACE, pygame.K_UP):
            if on_ground:
                vel_y = JUMP
        elif event.type == pygame.KEYUP and event.key in (pygame.K_SPACE, pygame.K_UP):
            if vel_y < -4:
                vel_y = -4

    keys = pygame.key.get_pressed()
    dx = 0
    if keys[pygame.K_LEFT]:
        dx -= SPEED
    if keys[pygame.K_RIGHT]:
        dx += SPEED

    player.x += dx
    for wall in walls:
        if player.colliderect(wall):
            if dx > 0:
                player.right = wall.left
            elif dx < 0:
                player.left = wall.right

    vel_y = min(vel_y + GRAVITY, MAX_FALL)
    player.y += vel_y
    on_ground = False
    for wall in walls:
        if player.colliderect(wall):
            if vel_y > 0:
                player.bottom = wall.top
                on_ground = True
            elif vel_y < 0:
                player.top = wall.bottom
            vel_y = 0

    blobs.update()

    for y in range(0, 360, 72):
        for x in range(0, 576, 72):
            screen.blit(background, (x, y))
    for wall in walls:
        screen.blit(block_img, wall)
    for blob in blobs:
        screen.blit(blob.image, blob.image.get_rect(midbottom=blob.rect.midbottom))
    screen.blit(player_img, player)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()