为什么在我为“ Pong”编码时，球无法在Pygame的代码中移动？ 有人可以帮我检查我的代码吗？

Question

I am a beginner in Pygame. I have coded a function for moving two balls in different direction and I follow the instructions coding it but it seems to be not working. I can draw two balls in screen but they will not move. I fixed it for almost 1 hour but no idea why balls aren't moving.

So, Can someone helps me check my code and just give me some hints. I will really appreciate anyone who helps me!

My code shows below

import pygame,sys,time
from pygame.locals import *

# User define function
def ball_move(Surface,white,pos,rad,speed):
    size=Surface.get_size()
    for item in [0,1]:
        pos[item]=pos[item]+speed[item]
        if pos[item]<rad:
            speed[item]=-speed[item]
        if pos[item]+rad>size[item]:
            speed[item]=-speed[item]

# Open a brand-new window

pygame.init()
Screen_size = (500,400)
Title = ('Pong')
Frame_Delay = 0.01
Surface= pygame.display.set_mode(Screen_size,0,0)
pygame.display.set_caption(Title)

# Set up white color for drawing balls

white=pygame.Color('white')

# Now, we start to draw two balls

pos1=(100,200)
pos2=(400,200)
rad=10
ball1=pygame.draw.circle(Surface,white,pos1,rad,0)
ball2=pygame.draw.circle(Surface,white,pos2,rad,0)
pygame.display.update()

# Now, define speed
speed1=(2,-2)
speed2=(-2,2)

# Now, we define a loop
while ball1:
    for event in pygame.event.get():
        if event.type == pygame.QUIT: 
            sys.exit()

# Now, we move the ball
ball1move=ball_move(Surface,white,pos1,rad,speed1)
ball2move=ball_move(Surface,white,pos2,rad,speed2)
pygame.draw.circle(Surface,white,pos1,rad,0,0)
pygame.draw.circle(Surface,white,pos2,rad,0,0)
surface.fill(pygame.Color('black'))

Answer 1

Part of saulspatz answer is correct, part is incorrect. You don't have to use sprites if you dont want to. pygame.draw is not pretty but perfectly usable. The main problem does seem to be your understanding of what to do in your event loop. All this should go in it:

while running:
    # Handdle your events
    # update your state
    # draw to your display
    pygame.display.update()

Also I notice in your unreachable code after the loop you are filling after your draws. Remember whether you fill , blit , or draw the latest thing goes over the rest. So for your example:

import pygame ,sys, time
from pygame.locals import *

# User define function
def ball_move(surface, pos, rad, speed):
    def _add(l_pos, l_speed, l_size):
        l_pos += l_speed
        if l_pos <= rad or l_pos >= l_size - rad:
            l_speed = -l_speed
        return l_pos, l_speed
    size = surface.get_size()
    pos_x, speed_x = _add(pos[0], speed[0], size[0])
    pos_y, speed_y = _add(pos[1], speed[1], size[1])
    return (pos_x, pos_y), (speed_x, speed_y)

pygame.init()
screen_size = (500, 400)
screen = pygame.display.set_mode(screen_size)
pygame.display.set_caption('Pong')
running = True

pos1 = (100, 200)
pos2 = (400, 200)
speed1 = (2, -2)
speed2 = (-2, 2)
rad = 10

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

    # update your state
    pos1, speed1 = ball_move(screen, pos1, rad, speed1)
    pos2, speed2 = ball_move(screen, pos2, rad, speed2)

    # draw to your display
    screen.fill(pygame.Color('black'))
    pygame.draw.circle(screen, pygame.Color('white'), pos1, rad)
    pygame.draw.circle(screen, pygame.Color('white'), pos2, rad)
    pygame.display.update()

Answer 2

There are a lot of problems with your code. The most basic is that you haven't figured out how event-driven programming works. You need to put the code that moves the balls inside your loop.

Another problem is that I don't think you want to use the pygame.draw module. It's been a long time since I wrote any pygame scripts, but as I remember, this module is useful for drawing fixed objects, like the background. A quick look at the docs seems to confirm this.

For moving objects, I think you need to look at the pygame.sprite module. Even if you got this code to work, it wouldn't move the balls. It would just draw a new ball at another position. So you would have first two balls, then four, then eight, ... . Sprites actually move. Not only is the object drawn at the new position, but it's erased at the old position. Your code don't address erasure at all.

Hope this helps.