落在平台上

本课属于 Coddy Pygame 学习旅程的“游戏世界”单元。第 16 课，共 36 课。

现在让墙壁支撑玩家。修正横向移动后，再沿 y 轴移动，并用同样的方法修正这次移动：如果玩家下落时与墙壁重叠，就把玩家的脚放到墙壁顶部。

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

每一帧开始时，on_ground 都会设为 False，只有落地时才会变为 True。走下平台边缘后，下一帧玩家下方就没有东西了，因此玩家会下落，并且无法在空中跳跃。

这会替换 FLOOR 这一行：地图的最底下一行和其他墙壁一样，都是地面。重力会让玩家每一帧向下陷入地面 1 个像素，而落地检测会把玩家抬回去，因此玩家会保持站立。

挑战

中等

让玩家落在平台上。

删除 FLOOR 行测试。
在 player.y += vel_y 之后，将 on_ground = False，然后遍历 walls。
对于玩家碰到的每面墙，如果 vel_y > 0：player.bottom = wall.top、vel_y = 0、on_ground = True。

按“开始”：玩家会落在下方的平台上。然后点击“检查”。

亲手试试

import pygame

TILE = 36
SPEED = 4
GRAVITY = 1
JUMP = -15
MAX_FALL = 12
FLOOR = 324

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

pygame.init()
screen = pygame.display.set_mode((576, 360))
pygame.display.set_caption("Landing")
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
    if player.bottom > FLOOR:
        player.bottom = FLOOR
        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