将摄像机限制在范围内

本课属于 Coddy Pygame 学习旅程的“游戏世界”单元。第 22 课，共 36 课。

始终让玩家位于画面中央的摄像机，在关卡开始时会显示关卡左侧的天空，在关卡结束后也会显示同样的天空。让摄像机保持在关卡边界内。

摄像机的最小值是 0：窗口从关卡左边缘开始。最大值是 level_width - WIDTH：窗口的右边缘与关卡的右边缘重合。跟随玩家后进行限制：

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

min 会降低摄像机的位置，避免它偏得太靠右；max 会提高摄像机的位置，避免它偏得太靠左。在关卡中间，两者都不会改变任何内容，摄像机仍像之前一样跟随玩家。靠近关卡两端时，摄像机会停下来，玩家则会向窗口边缘移动，这正是大多数横版卷轴游戏的表现方式。

挑战

简单

让摄像机在关卡两端停下。

找到这一行 camera_x = player.centerx - WIDTH // 2。
在它下面添加 camera_x = max(0, min(camera_x, level_width - WIDTH))。

按下“开始”：开始时，视野不再越过关卡的左边缘。然后按下“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

    camera_x = player.centerx - WIDTH // 2

    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()