四面八方

Coddy Pygame 项目：守住城堡课程的第 6 课，共 25 课。

一只史莱姆还算不上大群。怪物应该从窗口外的任意一侧进入。一个函数用 random.randint(0, 3) 选一侧，然后在这一侧随机选一个位置，距离边缘 24 像素。顶部和底部的写法如下：

side = random.randint(0, 3)
if side == 0:
    return (random.randint(0, WIDTH), -24)
if side == 1:
    return (random.randint(0, WIDTH), HEIGHT + 24)

然后每秒生成一个新的怪物。self.time % 60 每 60 帧会有一次结果为 0。创建新对象称为生成；为此单独编写一个方法 spawn，因为接下来的课会改变生成频率和怪物种类。

在怪物移动之前，在 update 中调用它，这样新怪物出现的那一帧就会迈出第一步。

挑战

简单

每秒从随机边缘生成一个史莱姆。

添加 import random 并编写 edge_point()：边缘 0 和 1 与上面相同，边缘 2 返回 (-24, random.randint(0, HEIGHT))，边缘 3 则在 WIDTH + 24 处生成。
从 Night.__init__ 中移除第一个史莱姆。
编写 spawn(self)：每 60 帧在 edge_point() 处生成一个史莱姆。在骑士移动后，于 update 中调用它。

按“开始”：每秒都会有一个史莱姆从边缘出现。然后点击“检查”。

亲手试试

import pygame

WIDTH, HEIGHT = 720, 480
TILE = 48
NIGHT = 60 * 60 * 4
WHITE = (240, 240, 240)

pygame.init()
screen = pygame.display.set_mode((WIDTH, HEIGHT))
pygame.display.set_caption("Hold the Keep")
clock = pygame.time.Clock()
font = pygame.font.Font("assets/fonts/pixel.ttf", 24)


def load(name):
    return pygame.image.load("assets/images/" + name).convert_alpha()


floor_img = load("floor.png")
wall_img = load("wall.png")
knight_img = load("knight.png")
MONSTERS = {
    "slime": {"image": load("slime.png"), "speed": 1.0},
}

courtyard = pygame.Rect(TILE, TILE, WIDTH - 2 * TILE, HEIGHT - 2 * TILE)
background = pygame.Surface((WIDTH, HEIGHT))
for row in range(HEIGHT // TILE):
    for col in range(WIDTH // TILE):
        x = col * TILE
        y = row * TILE
        if courtyard.collidepoint(x, y):
            background.blit(floor_img, (x, y))
        else:
            background.blit(wall_img, (x, y))


def draw(image, center):
    screen.blit(image, image.get_rect(center=center))


def clock_text(frames):
    seconds = frames // 60
    return f"{seconds // 60}:{seconds % 60:02d}"


class Knight(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        self.image = knight_img
        self.rect = pygame.Rect(0, 0, 24, 24)
        self.rect.center = courtyard.center
        self.speed = 3

    def move(self, keys):
        if keys[pygame.K_LEFT]:
            self.rect.x -= self.speed
        if keys[pygame.K_RIGHT]:
            self.rect.x += self.speed
        if keys[pygame.K_UP]:
            self.rect.y -= self.speed
        if keys[pygame.K_DOWN]:
            self.rect.y += self.speed
        self.rect.clamp_ip(courtyard)


class Monster(pygame.sprite.Sprite):
    def __init__(self, kind, pos):
        super().__init__()
        self.kind = kind
        self.image = MONSTERS[kind]["image"]
        self.speed = MONSTERS[kind]["speed"]
        self.pos = pygame.Vector2(pos)
        self.rect = pygame.Rect(0, 0, 28, 28)
        self.rect.center = self.pos

    def update(self, target):
        step = pygame.Vector2(target) - self.pos
        if step.length() > 0:
            self.pos += step.normalize() * self.speed
        self.rect.center = self.pos


class Night:
    def __init__(self):
        self.knight = Knight()
        self.time = 0
        self.monsters = pygame.sprite.Group()
        self.monsters.add(Monster("slime", (0, 0)))

    def update(self, keys):
        self.time += 1
        self.knight.move(keys)
        self.monsters.update(self.knight.rect.center)


night = Night()

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    night.update(pygame.key.get_pressed())

    screen.blit(background, (0, 0))
    knight = night.knight
    for monster in night.monsters:
        draw(monster.image, monster.rect.center)
    draw(knight.image, knight.rect.center)
    left = font.render(clock_text(max(0, NIGHT - night.time)) + " until dawn", True, WHITE)
    screen.blit(left, left.get_rect(center=(WIDTH // 2, 24)))
    pygame.display.flip()
    clock.tick(60)

pygame.quit()

Pygame 项目：守住城堡中的所有课

自己练习： Pygame 在线编辑器