撞到头

本课属于 Coddy Pygame 学习旅程的“游戏世界”单元。第 17 课，共 36 课。

跳到平台下方时，玩家会穿过平台向上移动，然后落在平台顶上。实体平台应该挡住玩家的头部。向上移动时，vel_y 是负数，所以在垂直循环中添加另一种情况：

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

玩家的头部会移到墙的底部，并且两种情况下速度都会变为 0。碰撞后，重力会立刻让玩家开始下落。如果没有 vel_y = 0，玩家会继续尝试向上移动，并卡在平台下方，直到重力耗尽这次跳跃的效果。

vel_y 的正负表示玩家是从哪一侧接触墙壁的，就像 dx 对墙壁的作用一样：下落时，玩家碰到墙的顶部；上升时，则碰到墙的底部。

挑战

简单

头部撞到平台时停止跳跃。

在垂直碰撞循环中，添加条件 vel_y < 0：player.top = wall.bottom。
在这两种情况下都设置 vel_y = 0，这样撞到平台时上升就会停止。

按“开始”并跳跃：头部会停在上方平台的下方。然后按“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("Head Bump")
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()

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)

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
                vel_y = 0
                on_ground = True

    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)
    screen.blit(player_img, player)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()

游戏世界中的所有课

自己练习： Pygame 在线编辑器