加权选择

本课属于 Coddy Pygame 学习旅程的“游戏规则”单元。第 18 课，共 30 课。

如果掉落的东西各不相同，游戏会更有趣。这里一半的掉落物是小石块，有些是大石块，还有少数是价值 5 分的宝石。random.choice 选中每个项目的机会都相同。random.choices 接受 weights，用来指定每个项目出现的频率：

def pick_kind():
    return random.choices(["small", "big", "gem"], weights=[5, 3, 2])[0]

权重 5、3 和 2 相加等于 10，所以每 10 个掉落物中，大约有 5 个小石块、3 个大石块和 2 颗宝石。权重表示比例，不是百分比：[50, 30, 20] 表示的比例相同。

random.choices 可以一次选出多个项目，所以它总是返回一个列表，即使只选一个也是如此。[0] 会从列表中取出该项目。

接着，每种掉落物都会变成不同的 Rect。宝石会放在单独的列表 gems 中，因为碰到宝石是好事。起始代码已经可以移动、绘制和接住宝石，但目前还不会掉落宝石。

挑战

中等

让大石块和宝石与小石块一起出现。

编写 pick_kind()：按权重 5、3 和 2 选择 "small"、"big" 或 "gem"。
触发 SPAWN 时，生成选中的物品：24 乘 24 的小石块、40 乘 40 的大石块（x 从 0 到 440，y 为 -40），或放入 gems 的 20 乘 20 宝石（x 从 0 到 460，y 为 -20）。

按“开始”：大石块和宝石也会落下。然后点击“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
SPAWN = pygame.USEREVENT + 2


def reset():
    global player, rocks, gems, score, lives
    player = pygame.Rect(220, 300, 40, 40)
    rocks = []
    gems = []
    score = 0
    lives = 3
    pygame.time.set_timer(POINT, 1000)
    pygame.time.set_timer(SPAWN, 500)


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))
    pygame.draw.rect(screen, (255, 196, 0), player)
    for rock in rocks:
        pygame.draw.rect(screen, (235, 80, 80), rock)
    for gem in gems:
        pygame.draw.rect(screen, (90, 220, 120), gem)
    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 rocks, gems, score, lives, state
    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())

    kept = []
    for rock in rocks:
        rock.y += 3
        if rock.colliderect(player):
            lives -= 1
        elif rock.top <= 360:
            kept.append(rock)
    rocks = kept
    kept = []
    for gem in gems:
        gem.y += 3
        if gem.colliderect(player):
            score += 5
        elif gem.top <= 360:
            kept.append(gem)
    gems = kept
    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 == SPAWN and state == "play":
            rocks.append(pygame.Rect(random.randint(0, 456), -24, 24, 24))
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_RETURN and state == "menu":
                reset()
                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()

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。

游戏规则中的所有课

自己练习： Pygame 在线编辑器