我如何链接蛇身体的运动？

Question

我想实现一个蛇游戏。蛇蜿蜒穿过操场。蛇每吃一些食物，蛇的长度就会增加一个元素。蛇身的元素像链子一样跟随它的头部。

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))

    # [...]

当蛇的头部向前移动时，我如何实现身体部位在其路径上跟随蛇的头部？

Answer 1

一般来说，您必须区分 2 种不同类型的蛇。在第一种情况下，蛇在一个网格中移动，每次当蛇移动时，它都会向前跨越网格中的一个领域。在另一种类型中，蛇的位置不在光栅中，也没有在网格的字段上捕捉，位置是自由的，蛇在字段中平滑滑动。
在以前，身体的每个元素都被捕捉到网格的领域，就像头部一样。另一个是更技巧，因为 body 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，它被捕捉到一个网格。

蛇的元素可以存储在元组列表中。每个元组包含网格中蛇元素的列和行。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)]

当蛇头移动(3, 3)到 ( 3, 2) 时，新的头部位置被添加到链表的头部 ( body.insert(0, (3, 2))：

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

最后去掉ist的尾部( 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放在列表中的位置上，就像链中的珍珠一样。

关键是，计算链中身体的最后一个元素与轨道上的后续位置之间的欧几里德距离。当找到距离足够大的新点时，将新珍珠（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然后甩头体的元件的数目和distance为欧几里得距离的元件之间。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()