每 800 ms 出现一块岩石

本课属于 Coddy Pygame 学习旅程的“游戏规则”单元。第 12 课，共 30 课。

一次只掉下一块石头，是个节奏平缓的游戏。设置计时器后，即使其他石头还在下落，每隔 800 ms 也会落下一块新石头。把石头放在列表中：

SPAWN = pygame.USEREVENT + 2
...
if event.type == SPAWN and state == "play":
    rocks.append(pygame.Rect(random.randint(0, 456), -24, 24, 24))

每个事件都有自己的编号，所以 SPAWN 是 USEREVENT + 2，比 POINT 大 1。在另一个计时器旁启动它的计时器，并在 reset() 中设置 rocks = []。

每一帧都移动所有石头，然后只保留仍在窗口内的石头：

for rock in rocks:
    rock.y += 4
rocks = [rock for rock in rocks if rock.top <= 360]

如果没有第二行，所有落下过的石头都会留在列表中。游戏会移动并检测成千上万块无人能看到的石头，而且你玩得越久，游戏就会越慢。

绘制和碰撞检测也会变成遍历 rocks 的循环。

挑战

中等

每隔 800 ms 掉下一块新岩石。

在 reset() 中，将 rock 设为空列表 rocks。
添加 SPAWN = pygame.USEREVENT + 2；reset() 将它的计时器设为 800 ms。
游戏进行时，SPAWN 会在 y 坐标为 -24、x 坐标随机取 0 到 456 的位置添加一块 24 乘 24 的岩石。
让岩石向下移动 4，保留顶部坐标不超过 360 的岩石，并绘制和检测每块岩石的碰撞。

按“开始”：多块岩石会同时落下。然后按“检查”。

亲手试试

import random
import pygame

pygame.init()
screen = pygame.display.set_mode((480, 360))
pygame.display.set_caption("Meteor Dodge")
clock = pygame.time.Clock()
heart = pygame.image.load("assets/images/heart.png").convert_alpha()
heart_empty = pygame.image.load("assets/images/heart_empty.png").convert_alpha()
font = pygame.font.Font("assets/fonts/pixel.ttf", 24)
big_font = pygame.font.Font("assets/fonts/pixel.ttf", 48)
WHITE = (240, 240, 240)
PLATE = (60, 60, 90)
POINT = pygame.USEREVENT + 1


def reset():
    global player, rock, score, lives, hit_time
    player = pygame.Rect(220, 300, 40, 40)
    rock = pygame.Rect(random.randint(0, 456), -24, 24, 24)
    score = 0
    lives = 3
    hit_time = -2000
    pygame.time.set_timer(POINT, 1000)


def draw_menu():
    screen.fill((30, 30, 46))
    title = big_font.render("Meteor Dodge", True, WHITE)
    title_rect = title.get_rect(center=(240, 140))
    pygame.draw.rect(screen, PLATE, title_rect.inflate(24, 12))
    screen.blit(title, title_rect)
    hint = font.render("Press Enter to play", True, WHITE)
    screen.blit(hint, hint.get_rect(center=(240, 200)))


def draw_game():
    screen.fill((30, 30, 46))
    safe = pygame.time.get_ticks() - hit_time < 1000
    if not safe or pygame.time.get_ticks() // 100 % 2 == 0:
        pygame.draw.rect(screen, (255, 196, 0), player)
    pygame.draw.rect(screen, (235, 80, 80), rock)
    score_text = font.render(f"{score:05}", True, WHITE)
    score_rect = score_text.get_rect(topright=(470, 10))
    pygame.draw.rect(screen, PLATE, score_rect.inflate(12, 8))
    screen.blit(score_text, score_rect)
    for i in range(3):
        if i < lives:
            screen.blit(heart, (10 + i * 40, 10))
        else:
            screen.blit(heart_empty, (10 + i * 40, 10))


def play_frame():
    global score, lives, state, hit_time
    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT]:
        player.x -= 6
    if keys[pygame.K_RIGHT]:
        player.x += 6
    player.clamp_ip(screen.get_rect())

    rock.y += 4
    if rock.top > 360:
        rock.y = -24
        rock.x = random.randint(0, 456)
    now = pygame.time.get_ticks()
    if rock.colliderect(player) and now - hit_time > 1000:
        hit_time = now
        lives -= 1
        if lives == 0:
            state = "over"
    draw_game()


def draw_over():
    draw_game()
    message = big_font.render("Game over", True, WHITE)
    screen.blit(message, message.get_rect(center=(240, 160)))
    hint = font.render("Press R to play again", True, WHITE)
    screen.blit(hint, hint.get_rect(center=(240, 200)))


reset()
state = "menu"

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        if event.type == POINT and state == "play":
            score += 1
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_RETURN and state == "menu":
                state = "play"
            elif event.key == pygame.K_r and state == "over":
                reset()
                state = "play"

    if state == "menu":
        draw_menu()
    elif state == "play":
        play_frame()
    else:
        draw_over()
    pygame.display.flip()
    clock.tick(60)

pygame.quit()