PyGame 如何让球从墙上反弹？

Question

在你批评我没有谷歌搜索或没有做研究之前，我事先做了研究但无济于事。

我正在尝试创建 Atari Breakout 游戏。我目前坚持让球从墙上反弹。我对此进行了研究，发现很多博客和 YouTube 视频（以及 Stack Overflow 问题： and ）都在谈论 PyGame 的 vector2 class。我还阅读了关于 vector2 的 PyGame 文档，但我不知道如何让它工作。

我目前正在编写一个脚本，让球从墙上反弹。一开始，要求玩家按下空格键，球会自动向东北方向移动。它应该在撞到顶壁时弹开，但相反，它进入了内部。这是我的方法：

import pygame
pygame.init()

screenWidth = 1200
screenHeight = 700

window = pygame.display.set_mode((screenWidth,screenHeight))
pygame.display.set_caption('Atari Breakout')

class Circle():

    def __init__(self, x, y, radius):
        self.x = x
        self.y = y
        self.radius = radius
        self.vel_x = 1
        self.vel_y = 1


def check_hit():
    global hit
    if (((screenWidth-box.x)<=box.radius) or ((box.x)<=box.radius) or ((box.y)<=box.radius) or ((screenHeight-box.y)<=box.radius)):
        # meaning  hit either four walls
        if (((screenWidth-box.x)<=box.radius) or ((box.x)<=box.radius)):
            # hit right, left
            print('hit right, left')
            hit = True
        elif (((box.y)<=box.radius) or ((screenHeight-box.y)<=box.radius)):
            # hit top, bottom
            print('hit top, bottom')
            hit = True
            

# main loop
run = True
box = Circle(600,300,10)
hit = False
                                                  # (screenWidth-box.x)<=box.radius     hit right wall
while run:                                        # (box.x)<=box.radius                 hit left wall
                                                  # (box.y)<=box.radius                 hit top wall                        
    pygame.time.Clock().tick(60)                  # (screenHeight-box.y)<=box.radius    hit bottom wall

    for event in pygame.event.get():
        if event == pygame.QUIT:
            run = False

    keys = pygame.key.get_pressed()

    if keys[pygame.K_SPACE] and (box.y)>box.radius:
        while True:
            box.y -= box.vel_y        
            box.x += box.vel_x

            window.fill((0,0,0))
            pygame.draw.circle(window, (44,176,55), (box.x, box.y), box.radius)
            pygame.display.update()

            check_hit()
            if hit == False:
                continue
            elif hit == True:
                break

        if (box.y)<=box.radius or (screenHeight-box.y)<=box.radius:
            # hit top, bottom
            box.vel_x *= 1
            box.vel_y *= -1
            print('changed')

            if (box.y)<=box.radius:
                # hit top
                print('hi')
                while True:
                    box.x += box.vel_x               # <-- myguess is this is the problem
                    box.y += box.vel_y


                    window.fill((0,0,0))
                    pygame.draw.circle(window, (44,176,55), (box.x, box.y), box.radius)
                    pygame.display.update()
                



        elif (screenWidth-box.x)<=box.radius or (box.x)<=box.radius:
            # hit right, left
            box.vel_x *= -1
            box.vel_y *= 1






    window.fill((0,0,0))
    pygame.draw.circle(window, (44,176,55), (box.x, box.y), box.radius)
    pygame.display.update()


    print('Where are you going')

pygame.quit()

我想问题出在我标记的地方。这是在这里：

        if (box.y)<=box.radius or (screenHeight-box.y)<=box.radius:
            # hit top, bottom
            box.vel_x *= 1
            box.vel_y *= -1
            print('changed')

            if (box.y)<=box.radius:
                # hit top
                print('hi')
                while True:
                    box.x += box.vel_x               # <-- myguess is this is the problem
                    box.y += box.vel_y


                    window.fill((0,0,0))
                    pygame.draw.circle(window, (44,176,55), (box.x, box.y), box.radius)
                    pygame.display.update()

但我不知道为什么。我的理论是：球向上移动，它撞到顶壁，check_hit() 踢进并使 hit = True，然后 vel_x 和 vel_y 相应改变（如果撞到顶墙，vel_x 应该保持不变，而 vel_y 应该乘以 -1）。然后它会向下移动，因此从顶壁“反弹”。

注意：目前我只有顶墙在工作。等我能想出如何先从顶墙上弹下来的时候再做其他三个。

你能帮我看看是什么问题吗？而如果这种操作需要用到vector2class，能不能解释一下或者给个学习的地方？

Answer 1

问题在于多个嵌套循环。你有一个应用程序循环，所以使用它。
在循环中连续移动球：

box.y -= box.vel_y        
box.x += box.vel_x

通过pygame.Rect对象为球定义一个矩形区域：

bounds = window.get_rect() # full screen

或

bounds = pygame.Rect(450, 200, 300, 200)  # rectangular region

改变球出界时的运动方向：

if box.x - box.radius < bounds.left or box.x + box.radius > bounds.right:
    box.vel_x *= -1 
if box.y - box.radius < bounds.top or box.y + box.radius > bounds.bottom:
    box.vel_y *= -1

看例子：

box = Circle(600,300,10)

run = True
start = False
clock = pygame.time.Clock()

while run:                     
    clock.tick(120)  

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    keys = pygame.key.get_pressed()
    if keys[pygame.K_SPACE]:
        start = True

    bounds = pygame.Rect(450, 200, 300, 200)
    if start:
        box.y -= box.vel_y        
        box.x += box.vel_x

        if box.x - box.radius < bounds.left or box.x + box.radius > bounds.right:
            box.vel_x *= -1 
        if box.y - box.radius < bounds.top or box.y + box.radius > bounds.bottom:
            box.vel_y *= -1 

    window.fill((0,0,0))
    pygame.draw.rect(window, (255, 0, 0), bounds, 1)
    pygame.draw.circle(window, (44,176,55), (box.x, box.y), box.radius)
    pygame.display.update()

PyGame 如何让球从墙上反弹？

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