Pygame：让球彼此弹开

Question

我试图让球互相弹跳，尝试使用 reflect() 方法来实现，但由于某些原因它无法正常工作。 为了检测球，我使用了 groupcollide 方法，因为我想不到更好的方法，也许这样做是错误的？

import pygame
import random

class Ball(pygame.sprite.Sprite):

    def __init__(self, startpos, velocity, startdir):
        super().__init__()
        self.pos = pygame.math.Vector2(startpos)
        self.velocity = velocity
        self.dir = pygame.math.Vector2(startdir).normalize()
        self.image = pygame.image.load("small_ball.png").convert_alpha()
        self.rect = self.image.get_rect(center = (round(self.pos.x), round(self.pos.y)))

    def reflect(self, NV):
        self.dir = self.dir.reflect(pygame.math.Vector2(NV))

    def update(self):
        self.pos += self.dir * 10
        self.rect.center = round(self.pos.x), round(self.pos.y)

        if self.rect.left <= 0:
            self.reflect((1, 0))
        if self.rect.right >= 700:
            self.reflect((-1, 0))
        if self.rect.top <= 0:
            self.reflect((0, 1))
        if self.rect.bottom >= 700:
            self.reflect((0, -1))

pygame.init()
window = pygame.display.set_mode((700, 700))
pygame.display.set_caption('noname')
clock = pygame.time.Clock()

all_balls = pygame.sprite.Group()

start, velocity, direction = (200, 200), 10, (random.random(), random.random())
ball_1 = Ball(start, velocity, direction)

start, velocity, direction = (200, 200), 10, (random.random(), random.random())
ball_2 = Ball(start, velocity, direction)

all_balls.add(ball_1, ball_2)

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

    all_balls.update()

    hits = pygame.sprite.groupcollide(all_balls, all_balls, False, False)
    for _, hit_sprites in hits.items():
        if len(hit_sprites) > 1:
            sprite_1 = hit_sprites[0]
            sprite_2 = hit_sprites[1]
            sprite_1.reflect((0, 1)) # not working
            print("hit!")

    window.fill(0)
    pygame.draw.rect(window, (255, 0, 0), (0, 0, 700, 700), 1)
    all_balls.draw(window)
    pygame.display.flip()

- Coffee inTime

---

你需要定义一个圆来代表球。然后，你可以使用Pygame如何让球碰撞中的算法来使球弹起。 - Rabbid76

Answer 1

通过球形精灵定义一个圆，并使用Pygame如何让球碰撞中提供的算法编写一个函数，可以计算反弹球的反射：

def reflectBalls(ball_1, ball_2):
    v1 = pygame.math.Vector2(ball_1.rect.center)
    v2 = pygame.math.Vector2(ball_2.rect.center)
    r1 = ball_1.rect.width // 2
    r2 = ball_2.rect.width // 2
    if v1.distance_to(v2) < r1 + r2 - 2:
        nv = v2 - v1
        if nv.length() > 0:
            ball_1.dir = ball_1.dir.reflect(nv)
            ball_2.dir = ball_2.dir.reflect(nv)

确保球的初始位置不同：

start, velocity, direction = (200, 200), 10, (random.random(), random.random())
ball_1 = Ball(start, velocity, direction)

start, velocity, direction = (300, 300), 10, (random.random(), random.random())
ball_2 = Ball(start, velocity, direction)

你也可以通过改进弹跳算法来避免球粘在一起。只有当下一个位置比当前位置更接近时，才会使球弹跳：

def reflectBalls(ball_1, ball_2):
    v1 = pygame.math.Vector2(ball_1.rect.center)
    v2 = pygame.math.Vector2(ball_2.rect.center)
    r1 = ball_1.rect.width // 2
    r2 = ball_2.rect.width // 2
    d = v1.distance_to(v2)
    if d < r1 + r2 - 2:
        dnext = (v1 + ball_1.dir).distance_to(v2 + ball_2.dir)
        nv = v2 - v1
        if dnext < d and nv.length() > 0:
            ball_1.dir = ball_1.dir.reflect(nv)
            ball_2.dir = ball_2.dir.reflect(nv)

测试每个球是否与任何其他球相撞：

ball_list = all_balls.sprites()
for i, b1 in enumerate(ball_list):
    for b2 in ball_list[i+1:]:
        reflectBalls(b1, b2)

---

完整示例： repl.it/@Rabbid76/PyGame-BallsBounceOff

import pygame
import random

class Ball(pygame.sprite.Sprite):

    def __init__(self, startpos, velocity, startdir):
        super().__init__()
        self.pos = pygame.math.Vector2(startpos)
        self.velocity = velocity
        self.dir = pygame.math.Vector2(startdir).normalize()
        self.image = pygame.image.load("small_ball.png").convert_alpha()
        self.rect = self.image.get_rect(center = (round(self.pos.x), round(self.pos.y)))

    def reflect(self, NV):
        self.dir = self.dir.reflect(pygame.math.Vector2(NV))

    def update(self):
        self.pos += self.dir * 10
        self.rect.center = round(self.pos.x), round(self.pos.y)

        if self.rect.left <= 0:
            self.reflect((1, 0))
            self.rect.left = 0
        if self.rect.right >= 700:
            self.reflect((-1, 0))
            self.rect.right = 700
        if self.rect.top <= 0:
            self.reflect((0, 1))
            self.rect.top = 0
        if self.rect.bottom >= 700:
            self.reflect((0, -1))
            self.rect.bottom = 700

pygame.init()
window = pygame.display.set_mode((700, 700))
pygame.display.set_caption('noname')
clock = pygame.time.Clock()

all_balls = pygame.sprite.Group()

start, velocity, direction = (200, 200), 10, (random.random(), random.random())
ball_1 = Ball(start, velocity, direction)

start, velocity, direction = (300, 300), 10, (random.random(), random.random())
ball_2 = Ball(start, velocity, direction)

all_balls.add(ball_1, ball_2)

def reflectBalls(ball_1, ball_2):
    v1 = pygame.math.Vector2(ball_1.rect.center)
    v2 = pygame.math.Vector2(ball_2.rect.center)
    r1 = ball_1.rect.width // 2
    r2 = ball_2.rect.width // 2
    d = v1.distance_to(v2)
    if d < r1 + r2 - 2:
        dnext = (v1 + ball_1.dir).distance_to(v2 + ball_2.dir)
        nv = v2 - v1
        if dnext < d and nv.length() > 0:
            ball_1.reflect(nv)
            ball_2.reflect(nv)

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

    all_balls.update()

    ball_list = all_balls.sprites()
    for i, b1 in enumerate(ball_list):
        for b2 in ball_list[i+1:]:
            reflectBalls(b1, b2)

    window.fill(0)
    pygame.draw.rect(window, (255, 0, 0), (0, 0, 700, 700), 1)
    all_balls.draw(window)
    pygame.display.flip()

- Rabbid76

---

谢谢您的反馈，乍一看我很喜欢这个解决方案，但我注意到有时球会不正确地飞出去，可能是什么问题呢？特别是在三个球的情况下尤为明显。 - Coffee inTime

@CoffeeinTime 这是由于velocity大于1的原因导致的。这会导致在球接触时无法精确检测到碰撞。当检测到碰撞时，球已经重叠了。现在需要你来改进算法。 - Rabbid76