如何让蛇生长并锁住蛇身体的运动？

Question

我想实现一个贪吃蛇游戏。蛇蜿蜒穿过操场。每次当蛇吃一些食物，蛇的长度增加一个元素。 蛇身的元素像链条一样跟随它的头部。

snake_x, snake_y = WIDTH//2, HEIGHT//2
body = []
move_x, move_y = (1, 0)
food_x, food_y = new_food(body)

run = True
while run:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT: move_x, move_y = (-1, 0)
            elif event.key == pygame.K_RIGHT: move_x, move_y = (1, 0)
            elif event.key == pygame.K_UP: move_x, move_y = (0, -1)
            elif event.key == pygame.K_DOWN: move_x, move_y = (0, 1)

    snake_x = (snake_x + move_x) % WIDTH
    snake_y = (snake_y + move_y) % HEIGHT 
    if snake_x == food_x and snake_y == food_y:
        food_x, food_y = new_food(body)
        body.append((snake_x, snake_x))

    # [...]

当蛇头向前移动时，我如何实现身体部位跟随蛇头的路径？

Answer 1

一般来说，你必须区分两种不同类型的蛇.在第一种情况下，蛇在一个网格中移动，蛇每移动一次，它就会在网格中向前迈出一个领域。在另一种类型中，蛇的位置不在光栅中，也没有捕捉到网格的区域，位置是自由的，蛇在区域中顺利滑动。
在前者中，身体的每个元素都被捕捉到网格的区域，就像头部一样。另一个更诡异，因为身体元素的位置取决于元素的大小和蛇头的动态、先前位置。

---

首先是蛇, 捕捉到网格。

蛇的元素可以存储在元组列表中。每个元组包含网格中 snakes 元素的列和行。列表中项目的变化直接跟随蛇的移动。如果蛇移动，则将新位置添加到列表的头部并删除列表的尾部。

例如，我们有一条具有以下元素的蛇：

body = [(3, 3), (3, 4), (4, 4), (5, 4), (6, 4)]

当蛇头从(3, 3)移动到(3, 2)时，新的头部位置被添加到列表的头部(body.insert(0, (3, 2))：

body = [(3, 2), (3, 3), (3, 4), (4, 4), (5, 4), (6, 4)]

最后去掉了ist的尾巴（del body[-1]）：

body = [(3, 2), (3, 3), (3, 4), (4, 4), (5, 4)]

最小的例子： repl.it/@Rabbid76/PyGame-SnakeMoveInGrid

import pygame
import random

pygame.init()
COLUMNS, ROWS, SIZE = 10, 10, 20
screen = pygame.display.set_mode((COLUMNS*SIZE, ROWS*SIZE))
clock  = pygame.time.Clock()

background = pygame.Surface((COLUMNS*SIZE, ROWS*SIZE))
background.fill((255, 255, 255))
for i in range(1, COLUMNS):
    pygame.draw.line(background, (128, 128, 128), (i*SIZE-1, 0), (i*SIZE-1, ROWS*SIZE), 2)
for i in range(1, ROWS):
    pygame.draw.line(background, (128, 128, 128), (0, i*SIZE-1), (COLUMNS*SIZE, i*SIZE-1), 2)

def random_pos(body):
    while True:
        pos = random.randrange(COLUMNS), random.randrange(ROWS)
        if pos not in body:
            break     
    return pos

length = 1
body = [(COLUMNS//2, ROWS//2)]
dir = (1, 0)
food = random_pos(body)

run = True
while run:
    clock.tick(5)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT: dir = (-1, 0)
            elif event.key == pygame.K_RIGHT: dir = (1, 0)
            elif event.key == pygame.K_UP: dir = (0, -1)
            elif event.key == pygame.K_DOWN: dir = (0, 1)

    body.insert(0, body[0][:])    
    body[0] = (body[0][0] + dir[0]) % COLUMNS, (body[0][1] + dir[1]) % ROWS
    if body[0] == food:
        food = random_pos(body)
        length += 1
    while len(body) > length:
        del body[-1] 
    
    screen.blit(background, (0, 0))
    pygame.draw.rect(screen, (255, 0, 255), (food[0]*SIZE, food[1]*SIZE, SIZE, SIZE))
    for i, pos in enumerate(body):
        color = (255, 0, 0) if i==0 else (0, 192, 0) if (i%2)==0 else (255, 128, 0)
        pygame.draw.rect(screen, color, (pos[0]*SIZE, pos[1]*SIZE, SIZE, SIZE))
    pygame.display.flip()

---

现在蛇完全自由定位。

我们必须在列表中跟踪蛇头访问过的所有位置。我们必须将蛇体的元素像链中的珍珠一样放置在列表中的位置上。

关键是计算链中主体的最后一个元素与轨道上后续位置之间的Euclidean distance。 当找到一个距离足够大的新点时，就会将一个新的珍珠（元素）添加到链（主体）中。

dx, dy = body[-1][0]-pos[0], body[-1][1]-pos[1]
if math.sqrt(dx*dx + dy*dy) >= distance:
    body.append(pos)

以下函数有 3 个参数。 track 是头部位置列表。 no_pearls 是 shakes 主体的元素数，distance 是元素之间的 Euclidean distance。该函数创建并返回蛇身体位置的列表。

def create_body(track, no_pearls, distance):
    body = [(track[0])]
    track_i = 1
    for i in range(1, no_pearls):
        while track_i < len(track):
            pos = track[track_i]
            track_i += 1
            dx, dy = body[-1][0]-pos[0], body[-1][1]-pos[1]
            if math.sqrt(dx*dx + dy*dy) >= distance:
                body.append(pos)
                break
    while len(body) < no_pearls:
        body.append(track[-1])
    del track[track_i:]
    return body

最小的例子： repl.it/@Rabbid76/PyGame-SnakeMoveFree

import pygame
import random
import math

pygame.init()
COLUMNS, ROWS, SIZE = 10, 10, 20
WIDTH, HEIGHT = COLUMNS*SIZE, ROWS*SIZE
screen = pygame.display.set_mode((WIDTH, HEIGHT))
clock  = pygame.time.Clock()

background = pygame.Surface((WIDTH, HEIGHT))
background.fill((255, 255, 255))
for i in range(1, COLUMNS):
    pygame.draw.line(background, (128, 128, 128), (i*SIZE-1, 0), (i*SIZE-1, ROWS*SIZE), 2)
for i in range(1, ROWS):
    pygame.draw.line(background, (128, 128, 128), (0, i*SIZE-1), (COLUMNS*SIZE, i*SIZE-1), 2)

def hit(pos_a, pos_b, distance):
    dx, dy = pos_a[0]-pos_b[0], pos_a[1]-pos_b[1]
    return math.sqrt(dx*dx + dy*dy) < distance

def random_pos(body):
    pos = None
    while True:
        pos = random.randint(SIZE//2, WIDTH-SIZE//2), random.randint(SIZE//2, HEIGHT-SIZE//2)
        if not any([hit(pos, bpos, 20) for bpos in body]):
            break    
    return pos

def create_body(track, no_pearls, distance):
    body = [(track[0])]
    track_i = 1
    for i in range(1, no_pearls):
        while track_i < len(track):
            pos = track[track_i]
            track_i += 1
            dx, dy = body[-1][0]-pos[0], body[-1][1]-pos[1]
            if math.sqrt(dx*dx + dy*dy) >= distance:
                body.append(pos)
                break
    while len(body) < no_pearls:
        body.append(track[-1])
    del track[track_i:]
    return body

length = 1
track = [(WIDTH//2, HEIGHT//2)]
dir = (1, 0)
food = random_pos(track)

run = True
while run:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT: dir = (-1, 0)
            elif event.key == pygame.K_RIGHT: dir = (1, 0)
            elif event.key == pygame.K_UP: dir = (0, -1)
            elif event.key == pygame.K_DOWN: dir = (0, 1)

    track.insert(0, track[0][:])    
    track[0] = (track[0][0] + dir[0]) % WIDTH, (track[0][1] + dir[1]) % HEIGHT

    body = create_body(track, length, 20)

    if hit(body[0], food, 20):
        food = random_pos(body)
        length += 1 
        
    screen.blit(background, (0, 0))
    pygame.draw.circle(screen, (255, 0, 255), food, SIZE//2)
    for i, pos in enumerate(body):
        color = (255, 0, 0) if i==0 else (0, 192, 0) if (i%2)==0 else (255, 128, 0)
        pygame.draw.circle(screen, color, pos, SIZE//2)
    pygame.display.flip()