Slimes on Patrol

Part of the Projects section of Coddy's Pygame journey. Lesson 24 of 31.

Each S on the map is a slime that slides along its row, 2 pixels a frame, and turns back at a wall.

An Enemy sprite keeps its own speed, dx and dy, so the same class can later make monsters that go up and down. Its update moves it, and if it now overlaps a block it steps back and reverses:

def update(self, blocks):
    self.rect.x += self.dx
    self.rect.y += self.dy
    if self.rect.collidelist(blocks) != -1:
        self.rect.x -= self.dx
        self.rect.y -= self.dy
        self.dx = -self.dx
        self.dy = -self.dy

rect.collidelist(rects) gives the index of the first Rect in the list that overlaps, or -1 when none does.

The slimes live in a Group, room.enemies. room.enemies.update(room.walls + [room.door]) calls update on every slime with that list. The door is always in it, so a slime never wanders out of an open door.

random.choice([-2, 2]) starts each slime left or right, so no two games play the same.

Challenge

Medium

Add import random at the top.
Write class Enemy(pygame.sprite.Sprite) with __init__(self, image, rect, dx, dy), which keeps all four as attributes, and the update method above.
In Room, set self.enemies = pygame.sprite.Group(). An S adds Enemy(slime_img, cell_rect(col, row), speed, 0) with speed = random.choice([-2, 2]).
Each frame, after the door, call room.enemies.update(room.walls + [room.door]).
Draw each enemy with draw(enemy.image, enemy.rect), before the knight.

Try it yourself

import pygame

TILE = 48
MAP = [
    "##############",
    "#............#",
    "#.P......K...#",
    "#............#",
    "#....##......D",
    "#....##......#",
    "##.#######.###",
    "#............#",
    "#...S....H...#",
    "##############",
]

pygame.init()
screen = pygame.display.set_mode((672, 480))
pygame.display.set_caption("Rune Keep")
clock = pygame.time.Clock()
font = pygame.font.Font("assets/fonts/pixel.ttf", 32)


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")
door_img = load("dungeon_door.png")
key_img = load("key.png")
slime_img = load("slime.png")
spider_img = load("spider.png")
heart_img = load("heart.png")
empty_img = load("heart_empty.png")
sword_img = load("sword.png")
potion_img = load("potion_red.png")


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


def cell_rect(col, row):
    rect = pygame.Rect(0, 0, 32, 32)
    rect.center = (col * TILE + 24, row * TILE + 24)
    return rect


class Room:
    def __init__(self, lines):
        self.walls = []
        self.start = (72, 72)
        self.has_key = False
        self.door_open = False
        for row, line in enumerate(lines):
            for col, char in enumerate(line):
                if char == "#":
                    self.walls.append(pygame.Rect(col * TILE, row * TILE, TILE, TILE))
                elif char == "P":
                    self.start = cell_rect(col, row).center
                elif char == "K":
                    self.key = cell_rect(col, row)
                elif char == "D":
                    self.door = pygame.Rect(col * TILE, row * TILE, TILE, TILE)

    def blocks(self):
        if self.door_open:
            return self.walls
        return self.walls + [self.door]


class Knight(pygame.sprite.Sprite):
    def __init__(self, center):
        super().__init__()
        self.image = knight_img
        self.rect = pygame.Rect(0, 0, 32, 32)
        self.rect.center = center

    def move(self, dx, dy, blocks):
        self.rect.x += dx
        for block in blocks:
            if self.rect.colliderect(block):
                if dx > 0:
                    self.rect.right = block.left
                elif dx < 0:
                    self.rect.left = block.right
        self.rect.y += dy
        for block in blocks:
            if self.rect.colliderect(block):
                if dy > 0:
                    self.rect.bottom = block.top
                elif dy < 0:
                    self.rect.top = block.bottom


room = Room(MAP)
knight = Knight(room.start)

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

    keys = pygame.key.get_pressed()
    dx = 0
    dy = 0
    if keys[pygame.K_LEFT]:
        dx = -3
    if keys[pygame.K_RIGHT]:
        dx = 3
    if keys[pygame.K_UP]:
        dy = -3
    if keys[pygame.K_DOWN]:
        dy = 3
    knight.move(dx, dy, room.blocks())
    knight.rect.clamp_ip(screen.get_rect())

    if not room.has_key and knight.rect.colliderect(room.key):
        room.has_key = True
    if room.has_key and knight.rect.inflate(8, 8).colliderect(room.door):
        room.door_open = True

    for row in range(10):
        for col in range(14):
            screen.blit(floor_img, (col * TILE, row * TILE))
    for wall in room.walls:
        screen.blit(wall_img, wall)
    if not room.door_open:
        screen.blit(door_img, room.door)
    if not room.has_key:
        draw(key_img, room.key)
    draw(knight.image, knight.rect)
    if room.has_key:
        screen.blit(key_img, (136, 6))
    pygame.display.flip()
    clock.tick(60)

pygame.quit()

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Projects

Practice on your own: Pygame playground