视差

本课属于 Coddy Pygame 学习旅程的“游戏世界”单元。第 23 课，共 36 课。

从行驶中的火车向外看：栅栏飞快地掠过，远处的山丘几乎没有移动。画远处的物体时让它们比近处的物体移动得慢，会让平面游戏更有纵深感。这叫作视差。

绘制云朵背景时，让它随摄像机移动的距离只有三分之一。背景每隔 72 像素就会重复，所以只需关注 camera_x // 3 % 72：图片滑过整张后，看起来就会和之前一样。

shift = camera_x // 3 % 72
for y in range(0, 360, 72):
    for x in range(-shift, WIDTH, 72):
        screen.blit(background, (x, y))

x 循环从窗口左侧的 -shift 开始，这样第一张副本滑出时仍会覆盖左边缘。瓦片和玩家仍使用完整的 camera_x：它们离得近。

挑战

中等

让背景比关卡滚动得慢。

不要使用 screen.fill，而是以 72 像素为间隔绘制背景（已在起始代码中加载）。
每一帧，将 shift = camera_x // 3 % 72 设为偏移量，并让每一行副本从 x = -shift 开始，以 72 为步长绘制，直到 WIDTH。
之后再绘制图块和玩家。

按“开始”并向右走：云朵会落在地面后面。然后点击“检查”。

亲手试试

import pygame

TILE = 36
WIDTH = 576
SPEED = 4
GRAVITY = 1
JUMP = -15
MAX_FALL = 12

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

pygame.init()
screen = pygame.display.set_mode((WIDTH, 360))
pygame.display.set_caption("Parallax")
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)

level_width = len(LEVEL[0]) * TILE
player = player_img.get_rect(midbottom=start)
vel_y = 0
on_ground = False
camera_x = 0

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

    camera_x = player.centerx - WIDTH // 2
    camera_x = max(0, min(camera_x, level_width - WIDTH))

    screen.fill((140, 200, 240))
    for wall in walls:
        screen.blit(block_img, (wall.x - camera_x, wall.y))
    screen.blit(player_img, (player.x - camera_x, player.y))
    pygame.display.flip()
    clock.tick(60)

pygame.quit()

自我测试

这节课包含一个小测验。开始学习即可作答，并记录你的进度。

游戏世界中的所有课

自己练习： Pygame 在线编辑器