我怎样才能让一个块跟随pygame中的另一个块[重复]

Question

我有两个块，一个由用户控制。当我移动我的街区时，我希望另一个街区跟随我。我试着做这样的事情

def follow():
    distance = math.hypot(abs(m.x - p.x), abs(m.y - p.y))
    angle_radians = math.atan2(abs(m.y - p.y), abs(m.x - p.x))
    if distance !=  0:
        p.y += math.sin(angle_radians)
        p.x += math.cos(angle_radians)

但是，块最终向与我完全相反的方向移动。任何帮助将不胜感激。

Answer 1

要使算法有效，您必须使用浮点数进行操作。如果m 和p 是pygame.Rect 对象，那么算法将不起作用，pygame.Rect 使用整数运算，小数部分会丢失。
注意 math.sin(angle_radians) 和 math.cos(angle_radians) 是

这意味着您必须将对象的位置存储在单独的变量中。假设您有浮点坐标 (mx, my) 和 (py, py)

你必须找到从（mx，my）到（px，py）的Unit vector。
单位向量可以通过将向量从 (mx, m.y) 到 (px, py) 除以它的长度来找到。
向量的长度可以通过Euclidean distance 来计算。
最后将向量乘以不大于点之间距离的比例（step）并将其添加到位置。例如：

stepDist = 1

# vector from (`mx`,  `my`) to (`px`, `py`)
dx, dy = p.y - mx, py - px

# [Euclidean distance](https://en.wikipedia.org/wiki/Euclidean_distance)
len = math.sqrt(dx*dx + dy*dy)

if len > 0:
    # [Unit vector](https://en.wikipedia.org/wiki/Unit_vector)
    ndx, ndy = dx/len, dy/len

    # minimum of step size and distance to target
    step = min(len, stepDist)

    # step forward
    px += ndx * step
    py += ndy * step

如果需要pygame.Rect对象，则可以设置矩形的位置。例如：

m.topleft = round(mx), round(my)
p.topleft = round(px), round(py)

但您不必分别将位置存储在 (mx, my) (px, py)。如果你分别做mx, my = m.topleft 和px, py = p.topleft，那么算法就会失败，因为分数部分会丢失。

Answer 2

如果我从 atan2() 中删除 abs()，代码对我有用

---

import pygame
import random
import math

# --- constants --- (UPPER_CASE_NAMES)

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600

FPS = 25 # for more than 220 it has no time to update screen

BLACK = (0, 0, 0)
WHITE = (255, 255, 255)

# --- classes --- (CamelCaseNames)

class Player(pygame.sprite.Sprite):

    def __init__(self, x=SCREEN_WIDTH//2, y=SCREEN_HEIGHT//2):
        super().__init__()
        self.image = pygame.image.load("image.png").convert()
        #self.rect = self.image.get_rect(x=x, y=y)
        self.rect = self.image.get_rect(centerx=x, centery=y)

    def update(self):
        #self.rect.centerx = random.randint(0, SCREEN_WIDTH)
        #self.rect.centery = random.randint(0, SCREEN_HEIGHT)
        move_x = random.randint(-15, 15)
        move_y = random.randint(-15, 15)
        self.rect.move_ip(move_x,move_y)

    def draw(self, surface):
        surface.blit(self.image, self.rect)

class Follower(Player):

    def update(self, player):
        distance = math.hypot(abs(player.rect.x - self.rect.x), abs(player.rect.y - self.rect.y))
        angle_radians = math.atan2((player.rect.y - self.rect.y), (player.rect.x - self.rect.x))

        if distance !=  0:
            self.rect.y += 5*math.sin(angle_radians)
            self.rect.x += 5*math.cos(angle_radians)        

# --- functions --- (lower_case_names)

# --- main ---

pygame.init()

screen = pygame.display.set_mode( (SCREEN_WIDTH, SCREEN_HEIGHT) )

player = Player()
follower = Follower(0, 0)

# --- mainloop ---

clock = pygame.time.Clock()

running = True
while running:

    # --- events ---
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

        elif event.type == pygame.KEYUP:
            if event.key == pygame.K_ESCAPE:
                running = False


    # --- changes/moves/updates ---

    if not pygame.key.get_pressed()[pygame.K_SPACE]:
        player.update()
        follower.update(player)
    # --- draws ---

    screen.fill(BLACK)

    player.draw(screen)
    follower.draw(screen)

    pygame.display.flip()

    # --- FPS ---

    ms = clock.tick(FPS)
    #pygame.display.set_caption('{}ms'.format(ms)) # 40ms for 25FPS, 16ms for 60FPS
    fps = clock.get_fps()
    pygame.display.set_caption('FPS: {}'.format(fps))

# --- end ---

pygame.quit()