Pong Tutorial using Pygame – Adding a Bouncing Ball

This tutorial is the third tutorial in a series of five Pygame tutorials:

• Pong Tutorial 1: Getting Started
• Pong Tutorial 2: Adding the Paddles
• Pong Tutorial 3: Controlling the Paddles
• Pong Tutorial 4: Adding a Bouncing Ball
• Pong Tutorial 5: Adding a Scoring system
• Extra: Pygame How To’s?

Our aim is to add the bouncing ball to our Pong game. To do so we will create a new class called Ball.

Bouncing Algorithm

• frame n: Sprite Coordinates: (x,y)
• frame n+1: Sprite Coordinates: (x+Vx,y+Vy)

As the sprite moves across the screen, it may need to bounce against another sprite or against the edge of the screen.

Let’s investigate how the velocity vector is affected when the sprite bounces against vertical and horizontal walls/edges.

Right Wall/EdgeLeft Wall/EdgeTop Wall/EdgeBottom Wall/Edge

Ball Class

import pygame
from random import randint
BLACK = (0,0,0)

class Ball(pygame.sprite.Sprite):
    #This class represents a ball. It derives from the "Sprite" class in Pygame.
    
    def __init__(self, color, width, height):
        # Call the parent class (Sprite) constructor
        super().__init__()
        
        # Pass in the color of the ball, its width and height.
        # Set the background color and set it to be transparent
        self.image = pygame.Surface([width, height])
        self.image.fill(BLACK)
        self.image.set_colorkey(BLACK)
 
        # Draw the ball (a rectangle!)
        pygame.draw.rect(self.image, color, [0, 0, width, height])
        
        self.velocity = [randint(4,8),randint(-8,8)]
        
        # Fetch the rectangle object that has the dimensions of the image.
        self.rect = self.image.get_rect()
        
    def update(self):
        self.rect.x += self.velocity[0]
        self.rect.y += self.velocity[1]

Adding the ball to the game

We will also apply the bouncing algorithm to check if it needs to bounce against any of the four walls. (See lines 67 to 75)

# Import the pygame library and initialise the game engine
import pygame
from paddle import Paddle
from ball import Ball

pygame.init()

# Define some colors
BLACK = (0,0,0)
WHITE = (255,255,255)

# Open a new window
size = (700, 500)
screen = pygame.display.set_mode(size)
pygame.display.set_caption("Pong")

paddleA = Paddle(WHITE, 10, 100)
paddleA.rect.x = 20
paddleA.rect.y = 200

paddleB = Paddle(WHITE, 10, 100)
paddleB.rect.x = 670
paddleB.rect.y = 200

ball = Ball(WHITE,10,10)
ball.rect.x = 345
ball.rect.y = 195

#This will be a list that will contain all the sprites we intend to use in our game.
all_sprites_list = pygame.sprite.Group()

# Add the paddles and the ball to the list of objects
all_sprites_list.add(paddleA)
all_sprites_list.add(paddleB)
all_sprites_list.add(ball)

# The loop will carry on until the user exits the game (e.g. clicks the close button).
carryOn = True
 
# The clock will be used to control how fast the screen updates
clock = pygame.time.Clock()
 
# -------- Main Program Loop -----------
while carryOn:
    # --- Main event loop
    for event in pygame.event.get(): # User did something
        if event.type == pygame.QUIT: # If user clicked close
              carryOn = False # Flag that we are done so we exit this loop
        elif event.type==pygame.KEYDOWN:
                if event.key==pygame.K_x: #Pressing the x Key will quit the game
                     carryOn=False
 
    #Moving the paddles when the use uses the arrow keys (player A) or "W/S" keys (player B) 
    keys = pygame.key.get_pressed()
    if keys[pygame.K_w]:
        paddleA.moveUp(5)
    if keys[pygame.K_s]:
        paddleA.moveDown(5)
    if keys[pygame.K_UP]:
        paddleB.moveUp(5)
    if keys[pygame.K_DOWN]:
        paddleB.moveDown(5)    
 
    # --- Game logic should go here
    all_sprites_list.update()
 
    #Check if the ball is bouncing against any of the 4 walls:
    if ball.rect.x>=690:
        ball.velocity[0] = -ball.velocity[0]
    if ball.rect.x<=0:
        ball.velocity[0] = -ball.velocity[0]
    if ball.rect.y>490:
        ball.velocity[1] = -ball.velocity[1]
    if ball.rect.y<0:
        ball.velocity[1] = -ball.velocity[1] 

    # --- Drawing code should go here
    # First, clear the screen to black. 
    screen.fill(BLACK)
    #Draw the net
    pygame.draw.line(screen, WHITE, [349, 0], [349, 500], 5)
    
    #Now let's draw all the sprites in one go. (For now we only have 2 sprites!)
    all_sprites_list.draw(screen) 
 
    # --- Go ahead and update the screen with what we've drawn.
    pygame.display.flip()
     
    # --- Limit to 60 frames per second
    clock.tick(60)
 
#Once we have exited the main program loop we can stop the game engine:
pygame.quit()

Collision Detection

So first, let’s add a new method called bounce() to our Ball class.

Then, in the main program loop, let’s add some code to detect if the ball sprite collides with the paddleA or paddleB sprites. If it does we will call the bounce() method of the Ball class.

import pygame
from random import randint
BLACK = (0, 0, 0)

class Ball(pygame.sprite.Sprite):
    #This class represents a ball. It derives from the "Sprite" class in Pygame.
    
    def __init__(self, color, width, height):
        # Call the parent class (Sprite) constructor
        super().__init__()
        
        # Pass in the color of the ball, and its x and y position, width and height.
        # Set the background color and set it to be transparent
        self.image = pygame.Surface([width, height])
        self.image.fill(BLACK)
        self.image.set_colorkey(BLACK)
 
        # Draw the ball (a rectangle!)
        pygame.draw.rect(self.image, color, [0, 0, width, height])
        
        self.velocity = [randint(4,8),randint(-8,8)]
        
        # Fetch the rectangle object that has the dimensions of the image.
        self.rect = self.image.get_rect()
        
    def update(self):
        self.rect.x += self.velocity[0]
        self.rect.y += self.velocity[1]
        
    def bounce(self):
        self.velocity[0] = -self.velocity[0]
        self.velocity[1] = randint(-8,8)

# Import the pygame library and initialise the game engine
import pygame
from paddle import Paddle
from ball import Ball

pygame.init()

# Define some colors
BLACK = (0,0,0)
WHITE = (255,255,255)

# Open a new window
size = (700, 500)
screen = pygame.display.set_mode(size)
pygame.display.set_caption("Pong")

paddleA = Paddle(WHITE, 10, 100)
paddleA.rect.x = 20
paddleA.rect.y = 200

paddleB = Paddle(WHITE, 10, 100)
paddleB.rect.x = 670
paddleB.rect.y = 200

ball = Ball(WHITE,10,10)
ball.rect.x = 345
ball.rect.y = 195

#This will be a list that will contain all the sprites we intend to use in our game.
all_sprites_list = pygame.sprite.Group()

# Add the paddles and the ball to the list of sprites
all_sprites_list.add(paddleA)
all_sprites_list.add(paddleB)
all_sprites_list.add(ball)

# The loop will carry on until the user exit the game (e.g. clicks the close button).
carryOn = True
 
# The clock will be used to control how fast the screen updates
clock = pygame.time.Clock()
 
# -------- Main Program Loop -----------
while carryOn:
    # --- Main event loop
    for event in pygame.event.get(): # User did something
        if event.type == pygame.QUIT: # If user clicked close
              carryOn = False # Flag that we are done so we exit this loop
        elif event.type==pygame.KEYDOWN:
                if event.key==pygame.K_x: #Pressing the x Key will quit the game
                     carryOn=False
 
    #Moving the paddles when the use uses the arrow keys (player A) or "W/S" keys (player B) 
    keys = pygame.key.get_pressed()
    if keys[pygame.K_w]:
        paddleA.moveUp(5)
    if keys[pygame.K_s]:
        paddleA.moveDown(5)
    if keys[pygame.K_UP]:
        paddleB.moveUp(5)
    if keys[pygame.K_DOWN]:
        paddleB.moveDown(5)    
 
    # --- Game logic should go here
    all_sprites_list.update()

    #Check if the ball is bouncing against any of the 4 walls:
    if ball.rect.x>=690:
        ball.velocity[0] = -ball.velocity[0]
    if ball.rect.x<=0:
        ball.velocity[0] = -ball.velocity[0]
    if ball.rect.y>490:
        ball.velocity[1] = -ball.velocity[1]
    if ball.rect.y<0:
        ball.velocity[1] = -ball.velocity[1] 
 
    #Detect collisions between the ball and the paddles
    if pygame.sprite.collide_mask(ball, paddleA) or pygame.sprite.collide_mask(ball, paddleB):
      ball.bounce()
 
    # --- Drawing code should go here
    # First, clear the screen to black. 
    screen.fill(BLACK)
    #Draw the net
    pygame.draw.line(screen, WHITE, [349, 0], [349, 500], 5)
    
    #Now let's draw all the sprites in one go. (For now we only have 2 sprites!)
    all_sprites_list.draw(screen) 
 
    # --- Go ahead and update the screen with what we've drawn.
    pygame.display.flip()
     
    # --- Limit to 60 frames per second
    clock.tick(60)
 
#Once we have exited the main program loop we can stop the game engine:
pygame.quit()

Next Step?