摄像机偏移

本课属于 Coddy Pygame 学习旅程的“游戏世界”单元。第 20 课，共 36 课。

这一关宽 48 个瓦片，相当于 3 个屏幕窗口。所有内容的位置都保持在关卡坐标中，由 camera 决定窗口显示关卡的哪一部分。摄像机的位置由一个数字表示，即 camera_x：窗口左边缘对应的关卡 x 坐标。

要绘制某个对象，请从它的关卡 x 坐标中减去摄像机的位置：

for wall in walls:
    screen.blit(block_img, (wall.x - camera_x, wall.y))
screen.blit(player_img, (player.x - camera_x, player.y))

当 camera_x = 0 时，你会看到关卡起点。当 camera_x = 600 时，x = 800 处的墙会绘制在 200 的位置。只有绘制位置会变化：walls 和 player 中的 Rect 会保持各自在关卡中的位置，因此碰撞仍会像之前一样正常工作。

在这个程序中，摄像机会自行向右移动，每帧移动 2 个像素，直到显示关卡终点。起始代码会移动 camera_x，但绘制时没有用到它，所以画面不会移动。

挑战

简单

通过摄像机绘制关卡。

在 (wall.x - camera_x, wall.y) 处绘制每面墙。
在 (player.x - camera_x, player.y) 处绘制玩家。
保持让 camera_x 持续移动的那一行不变。

按下“开始”：关卡会自动向左滑动。然后按“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("Camera")
clock = pygame.time.Clock()

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

    if camera_x < level_width - WIDTH:
        camera_x += 2

    screen.fill((140, 200, 240))
    for wall in walls:
        screen.blit(block_img, (wall.x, wall.y))
    screen.blit(player_img, (player.x, player.y))
    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