精灵在一定距离限制内遵循另一种灵活的方式[重复]答案

【问题标题】：Sprite follow another flexible way within certain distance limits [duplicate]精灵在一定距离限制内遵循另一种灵活的方式[重复]
【发布时间】：2020-05-20 17:01:32
【问题描述】：

我正在尝试让精灵遵循另一种精灵灵活的方式。

如果主精灵移动得更快，则跟随者会更落后，如果较慢的跟随者靠近。

运动本身适用于以下（伪）代码：

target_vector = Vector2D(mainsprite_x, mainsprite_y)
follower_vector = Vector2D(follower_x, follower_y)

new_follower_vector = Vector2D.lerp(follower_vector, target_vector, LERP_FACTOR)

目前我一直在为LERP_FACTOR 使用各种常量，这些常量“还可以”。

现在我想添加限制跟随者可以落后多少以及它可以有多接近。

我正在使用 Pygame，但这没关系。

我怎样才能做到这一点？

【问题讨论】：

标签： python pygame 2d-games 2d-vector

【解决方案1】：

我建议计算跟随者和精灵之间的距离以及从（follower_x，follower_y）到（mainsprite_x，mainsprite_y）的单位方向向量。
距离可以通过计算Euclidean distance 得到。 Pygame 为此提供了distance_to()。单位方向向量可以通过将方向向量除以距离或通过归一化（normalize()）方向向量来计算：

target_vector = Vector2(mainsprite_x, mainsprite_y)
follower_vector = Vector2(follower_x, follower_y)

distance = follower_vector.distance_to(target_vector)
direction_vector = target_vector - follower_vector
if distance > 0:
    direction_vector /= distance

现在你可以定义一个精确的step_distance 并移动到精灵的follower int 方向：

if distance > 0:
    new_follower_vector = follower_vector + direction_vector * step_distance.

定义一个maximum_distance 和一个minimum_distance。最小步距为：

min_step = max(0, distance - maximum_distance)

最大步距为

max_step = distance - minimum_distance

把它们放在一起：

minimum_distance    = ???
maximum_distance    = ???
target_vector       = Vector2(mainsprite_x, mainsprite_y)
follower_vector     = Vector2(follower_x, follower_y)
new_follower_vector = Vector2(follower_x, follower_y)

distance = follower_vector.distance_to(target_vector)
if distance > minimum_distance:
    direction_vector    = (target_vector - follower_vector) / distance
    min_step            = max(0, distance - maximum_distance)
    max_step            = distance - minimum_distance
    step_distance       = min_step + (max_step - min_step) * LERP_FACTOR
    new_follower_vector = follower_vector + direction_vector * step_distance

最小示例： repl.it/@Rabbid76/PyGame-FollowMouseSmoothly

import pygame

LERP_FACTOR      = 0.05
minimum_distance = 25
maximum_distance = 100

def FollowMe(pops, fpos):
    target_vector       = pygame.math.Vector2(*pops)
    follower_vector     = pygame.math.Vector2(*fpos)
    new_follower_vector = pygame.math.Vector2(*fpos)

    distance = follower_vector.distance_to(target_vector)
    if distance > minimum_distance:
        direction_vector    = (target_vector - follower_vector) / distance
        min_step            = max(0, distance - maximum_distance)
        max_step            = distance - minimum_distance
        step_distance       = min_step + (max_step - min_step) * LERP_FACTOR
        new_follower_vector = follower_vector + direction_vector * step_distance

    return (new_follower_vector.x, new_follower_vector.y) 

pygame.init()
window = pygame.display.set_mode((500, 500))
clock = pygame.time.Clock()

follower = (100, 100)
run = True
while run:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    player   = pygame.mouse.get_pos()
    follower = FollowMe(player, follower)

    window.fill(0)  
    pygame.draw.circle(window, (0, 0, 255), player, 10)
    pygame.draw.circle(window, (255, 0, 0), (round(follower[0]), round(follower[1])), 10)
    pygame.display.flip()

【讨论】：