不明白为什么物体会从墙上弹起 / Pygame

Question

So I was trying to do the DVD bounce on pygame and couldn't get it to hit the walls and bounce off but I eventually found someones elses method and used it but I can't figure out why it actually works , i don't understand why the DVD logo actually bounces off. If someone could help that would be very much appreciated.

import pygame
import os


os.chdir("C:\\Users\\user\\Documents\\Pythonscript\\DVD")

pygame.init()


def gameloop():

    width = 600
    height = 500
    screen = pygame.display.set_mode((width, height))
    pygame.display.set_caption('DVD')
    black = (0,0,0)
    dvd_logo = pygame.image.load("DVD Red.png")
    rect = dvd_logo.get_rect()
    clock = pygame.time.Clock()                             
    game = False
    move_speed = [2, 2]

    while not game:
            for event in pygame.event.get():
                    if event.type == pygame.QUIT:
                            game= True

            if rect.left < 0:
                move_speed[0] = -move_speed[0]
                dvd_logo = pygame.image.load("DVD Pink.png")
            if rect.right > width:
                move_speed[0] = -move_speed[0]
                dvd_logo = pygame.image.load("DVD Blue.png")
            if rect.top < 0:
                move_speed[1] = -move_speed[1]
                dvd_logo = pygame.image.load("DVD Yellow.png")
            if rect.bottom > height:
                move_speed[1] = -move_speed[1]
                dvd_logo = pygame.image.load("DVD Red.png")

            rect.left += move_speed[0]
            rect.top += move_speed[1]       
            screen.fill(black)
            screen.blit(dvd_logo, rect)
            pygame.display.flip()
            clock.tick(60)


gameloop()      
pygame.quit()
quit()

Answer 1

So the rect object represents the position and size of the dvd_logo image. In each frame, the code checks if the left of rect is less than zero (left edge of window), if right is greater than width (right edge of window), if top is less than zero (top edge of window), or bottom is greater than height (bottom edge of window). If the left or right are beyond the left or right edges, the move_speed[0] (left/right speed) is negated, and the same is true for top / bottom with move_speed[1] .

If your move_speed[0] is -2 (moving left) and rect.left is less than zero, move_speed[0] becomes 2 , so it'll move right instead of left. Again, same concept for top/bottom and move_speed[1].