被击中后保持安全

本课属于 Coddy Pygame 学习旅程的“游戏规则”单元。第 10 课，共 30 课。

在这个版本中，站到岩石下面。岩石撞到玩家后不再跳回顶部，而是会穿过玩家，并连续多帧碰到玩家。每一帧都会扣除一条命，所以一块岩石就能结束游戏。

很多游戏会在玩家受击后提供一小段安全时间。要知道经过了多久，可以查看时钟。pygame.time.get_ticks()表示自pygame.init()以来经过的毫秒数。记下受击的时刻，然后用当前时间减去它：

now = pygame.time.get_ticks()
if rock.colliderect(player) and now - hit_time > 1000:
    hit_time = now
    lives -= 1

在reset()中将hit_time设为-2000，这样第一次受击一定会生效。

让玩家闪烁，以显示安全时间。get_ticks() // 100 % 2会先保持 0 十分之一秒，然后变为 1，再变回 0，因此只在值为 0 时绘制玩家，就会让玩家闪烁：

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)

挑战

中等

让每次被击中只损失一条命，而不是三条。

在 reset() 中，将 hit_time = -2000 添加到 global 那一行。
只有在距离上次设置 hit_time 超过 1000 ms 后，被击中才会损失一条命；然后将 hit_time 设置为当前时间。
被击中后的 1000 ms 内，仅当 pygame.time.get_ticks() // 100 % 2 == 0 时绘制玩家。

按“开始”并被击中一次：一颗心会消失，玩家会闪烁。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)


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


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)
    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
    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)
        score += 1
    if rock.colliderect(player):
        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 == 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()

游戏规则中的所有课

自己练习： Pygame 在线编辑器