A Monster

Lesson 5 of 20 in Coddy's Pygame Project: Hold the Keep course.

A monster walks straight at the knight. pygame.Vector2 holds an x and a y that can have decimals, and you can add and subtract whole Vector2s:

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

step points from the monster to the knight, however far away. normalize() keeps its direction but makes it 1 pixel long, so times self.speed the monster moves exactly its speed each frame, in any direction. A Rect holds whole numbers only, so the exact place lives in self.pos and the Rect follows it.

Each kind of monster gets one row in a table, so adding a kind later is one line:

MONSTERS = {
    "slime": {"image": load("slime.png"), "speed": 1.0},
}

Monsters come in from outside the window. edge_point() picks a side with random.randint(0, 3) and a random place along it, 24 pixels out.

Challenge

Medium

import random and add the MONSTERS table with the slime.
Write edge_point(): side 0 is (random.randint(0, WIDTH), -24), 1 the same at HEIGHT + 24, 2 is (-24, random.randint(0, HEIGHT)) and 3 the same at WIDTH + 24.
Write class Monster(pygame.sprite.Sprite): __init__(self, kind, pos) keeps kind, image and speed from the table, pos as a Vector2 and a 28 by 28 rect centred on it; update(self, target) walks as above.
In Night: self.monsters = pygame.sprite.Group() with one slime at edge_point(); update calls self.monsters.update(self.knight.rect.center). Draw every monster with draw before the knight.

Try it yourself

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")

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 Night:
    def __init__(self):
        self.knight = Knight()
        self.time = 0

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


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
    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()