Pong on pygame, ball always bouncing despite not colliding with the paddle

Question

I'm failly new to programming in general and this is my second game ever so sorry in advance. I made a pong game with only one paddle for now, but the ball keeps bouncing even when it's not hitting the paddle. This is my draw ball function:

    def draw_ball(self): 
        self.sc.blit(ball, (self.bx,self.by))
        self.bx += self.speedx
        self.by += self.speedy

        if self.bx >= 1000:#check goals
            self.bx = 250
            self.by = 340

        if self.bx <= 38: #check coalision
            self.speedx *= -1
        if self.by<= 12: 
            self.speedy *= -1
        if  self.by>= 725: 
            self.speedy *= -1
        
        #check coalision with the paddle 
        #px and py are the coordinates of the paddle 
        if self.bx > (self.px - 35) and (self.by < (self.py + 196) and  (self.by + 38) > self.py) : 
            self.speedx *= -1

Here is the main loop:

#global variables
WIN_HEIGHT = 1024 
WIN_WIDTH = 768 
SPEED = 5 
PX = 956
PY  = 320 
MOVEMENT = 5
BALL = Ball(550, 60, screen, .5, .4, PX, PY)


running = True 
while running: 

  redraw_screen()

  for event in pygame.event.get():
    if event.type == pygame.QUIT:
      running = False
    mouse_pos = pygame.mouse.get_pos()
    if event.type == pygame.MOUSEBUTTONDOWN and START_BUTTON.is_clicked(mouse_pos):
      running = False
      playing = True

     while playing: 
        screen.fill((0,0,0))
        BALL.draw_ball()
        PLAYER.draw_player()
        pygame.display.flip()

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

Thanks for your help.

Check all of the places where you are changing `speedx`. Does the surrounding logic all make sense? (Hint: it doesn't) — 0x5453, Sep 04 '20 at 20:49
You've got `(self.py - 38) < self.by < (self.py + 196).` Is that what you need? What are the dimensions of the paddle re: `self.py`? — GAEfan, Sep 04 '20 at 20:53
38 is the dimension of the ball (38x38), 196x38 are the dimensions of the paddle. — stunerr, Sep 04 '20 at 22:23
The logic looks right. Do you have the full code posted somewhere for testing? — Mike67, Sep 04 '20 at 22:54

score 1 · Accepted Answer · answered Sep 05 '20 at 07:14

I recommend to use pygame.Rect objects and the method .colliderect()

Define rectangles for the ball, paddle and screen or get the rectangles from a pygame.Surface by .get_rect():

ball_rect = ball.get_rect(topleft = (self.bx, self.by))
right_paddle_rect = pygame.Rect(self.px, self.py, 38, 196)
screen_rect = self.sc.get_rect()

Test the collision of the ball and the borders of the screen:

if ball_rect.top < screen_rect.top or ball_rect.bottom > screen_rect.bottom:
    self.speedy *= -1
if ball_rect.left < screen_rect.left:
    self.speedx *= -1
if ball_rect.right > screen_rect.right:
    self.bx = 250
    self.by = 340

Be carful when you test the collision between the ball and the paddle. See Sometimes the ball doesn't bounce off the paddle in pong game:

if ball_rect.colliderect(right_paddle_rect):
            self.speedx = -abs(self.speedx)

Complete method draw_ball:

def draw_ball(self):
    self.sc.blit(ball, (self.bx, self.by))

    self.bx += self.speedx
    self.by += self.speedy

    ball_rect = ball.get_rect(topleft = (self.bx, self.by))
    right_paddle_rect = pygame.Rect(self.px, self.py, 38, 196)
    screen_rect = self.sc.get_rect()

    if ball_rect.top < screen_rect.top or ball_rect.bottom > screen_rect.bottom:
        self.speedy *= -1
    if ball_rect.left < screen_rect.left:
        self.speedx *= -1
    if ball_rect.right > screen_rect.right:
        self.bx = 250
        self.by = 340

    if ball_rect.colliderect(right_paddle_rect):
        self.speedx = -abs(self.speedx)

Minimal example:

import pygame

class Game:
    def __init__(self, screen):
        self.sc = screen
        self.bx, self.by = 250, 340
        self.speedx, self.speedy = 5, 5
        self.px, self.py = 700, 200

    def draw_ball(self):
        self.sc.blit(ball, (self.bx, self.by))

        self.bx += self.speedx
        self.by += self.speedy

        ball_rect = ball.get_rect(topleft = (self.bx, self.by))
        right_paddle_rect = pygame.Rect(self.px, self.py, 38, 196)
        screen_rect = self.sc.get_rect()

        if ball_rect.top < screen_rect.top or ball_rect.bottom > screen_rect.bottom:
            self.speedy *= -1
        if ball_rect.left < screen_rect.left:
            self.speedx *= -1
        if ball_rect.right > screen_rect.right:
            self.bx = 250
            self.by = 340

        if ball_rect.colliderect(right_paddle_rect):
            self.speedx = -abs(self.speedx) 

pygame.init()
screen = pygame.display.set_mode((800, 600))
clock = pygame.time.Clock()

ball = pygame.Surface((38, 38), pygame.SRCALPHA)
pygame.draw.circle(ball, (255, 255, 255), (19, 19), 19)
game = Game(screen)

run = True
while run:
    clock.tick(60)

    # event loop
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
        if event.type == pygame.KEYDOWN:
            print(pygame.key.name(event.key))

    keys = pygame.key.get_pressed()
    pspeed = 5
    if keys[pygame.K_UP]:
       game.py = max(0, game.py - pspeed) 
    if keys[pygame.K_DOWN]:
       game.py = min(screen.get_height()-196, game.py + pspeed) 

    screen.fill(0)
    game.draw_ball()
    pygame.draw.rect(screen, (255, 255, 255), (game.px, game.py, 38, 196)) 
    pygame.display.flip()

Thanks a lot! I still can't find whats wrong with my initial code but it has to do with the logic most likely but this works perfectly well. Much appreciated. — stunerr, Sep 06 '20 at 09:28

Pong on pygame, ball always bouncing despite not colliding with the paddle

1 Answers1