IPP-Project 4

“Pong”

In this project, we will build a version of Pong, one of the first arcade video games (1972). While Pong is not particularly exciting compared to today’s video games, Pong is relatively simple to build and provides a nice opportunity to work on the skills that you will need to build a game like Asteroids. As usual, we have provided a program template that can be used to guide your development of Pong.

Mini-project development process

1. Add code to the program template that draws a ball moving across the Pong table. We recommend that you add the positional update for the ball to the draw handler as shown in the second part of the “Motion” video.
2. Add code to the function spawn_ball that spawns a ball in the middle of the table and assigns the ball a fixed velocity (for now). Ignore the parameter direction at this point.
3. Add a call to spawn_ball in the function new_game which starts a game of Pong. Note that the program template also includes an initial call to new_game in the main body of your program to get a game going immediately.
4. Modify your code such that the ball collides with and bounces off of the top and bottom walls. Experiment with different hard-coded initial velocities to test your code.
5. Add randomization to the velocity in spawn_ball(direction) The velocity of the ball should be upwards and towards the right if direction == RIGHT and upwards and towards the left if direction == LEFT. The exact values for the horizontal and vertical components of this velocity should be generated using random.randrange(). For the horizontal velocity, we suggest a speed of around random.randrange(120, 240) pixels per second. For the vertical velocity, we suggest a speed of around random.randrange(60, 180) pixels per second. (You will need to set the signs of velocities appropriately.)
6. Add code to the draw handler that tests whether the ball touches/collides with the left and right gutters. (Remember that the gutters are offset from the left and right edges of the canvas by the width of the paddle as described in the “Pong” video.) When the ball touches a gutter, use either spawn_ball(LEFT) or spawn_ball(RIGHT) to respawn the ball in the center of the table headed towards the opposite gutter.
7. Next, add code that draws the left and right paddles in their respective gutters. The vertical positions of these two paddles should depend on two global variables. (In the template, the variables were paddle1_pos and paddle2_pos.)
8. Add code that modifies the values of these vertical positions via an update in the draw handler. The update should reference two global variables that contain the vertical velocities of the paddles. (In the template, the variables were paddle1_vel and paddle2_vel.)
9. Update the values of these two vertical velocities using key handlers. The “w” and “s” keys should control the vertical velocity of the left paddle while the “Up arrow” and “Down arrow” key should control the velocity of the right paddle. In our version of Pong, the left paddle moves up at a constant velocity if the “w” key is pressed and moves down at a constant velocity if the “s” is pressed and is motionless if neither is pressed. (The motion if both are pressed is up to you.) To achieve this effect, you will need to use both a keydown and a keyup handler to increase/decrease the vertical velocity in an appropriate manner.
10. Restrict your paddles to stay entirely on the canvas by adding a check before you update the paddles’ vertical positions in the draw handler. In particular, test whether the current update for a paddle’s position will move part of the paddle off of the screen. If it does, don’t allow the update.
11. Modify your collision code for the left and right gutters in step 6 to check whether the ball is actually striking a paddle when it touches a gutter. If so, reflect the ball back into play. This collision model eliminates the possibility of the ball striking the edge of the paddle and greatly simplifies your collision/reflection code.
12. To moderately increase the difficulty of your game, increase the velocity of the ball by 10% each time it strikes a paddle.
13. Add scoring to the game as shown in the Pong video lecture. Each time the ball strikes the left or right gutter (but not a paddle), the opposite player receives a point and ball is respawned appropriately.
14. Finally, add code to new_game which resets the score before calling spawn_ball. Add a “Restart” button that calls new_game to reset the score and relaunch the ball.

Your final version of Pong should be remarkably similar to the original arcade Pong game. Our full implementation of Pong took a little more than 100 lines of code with comments.

Grading Rubric - 19 pts total (scaled to 100 pts)

• 1 pt - The ball spawns in the middle of the canvas with either an upward left or an upward right velocity. No credit if the ball moves only horizontally left or right. Bleh, that would be boring!
• 2 pts - The ball bounces off of the top and bottom walls correctly. (1 pt each)
• 2 pts - The ball respawns in the middle of the screen when it strikes the left or right gutter but not the paddles. (1 pt for each side) Give credit for this item even if the ball hits the edge of the canvas instead of the gutter.
• 1 pt - The left and right gutters (instead of the edges of the canvas) are properly used as the edges of the table.
• 1 pt - The ball spawns moving towards the player that won the last point.
• 2 pts - The ‘w’ and ‘s’ keys correctly control the velocity of the left paddle as described above. Please test each key in isolation. (1 pt if the paddle moves, but in an incorrect manner in response to ‘w’ and ‘s’ key presses.)
• 2 pts - The up and down arrows keys correctly control the velocity of the right paddle as described above. Please test each key in isolation. (1 pt if the paddle moves, but in an incorrect manner in response to up and down arrow key presses.)
• 2 pts - The edge of each paddle is flush with the gutter. (1 pt per paddle)
• 2 pts - The paddles stay on the canvas at all times. (1 pt per paddle)
• 2 pts - The ball correctly bounces off the left and right paddles. (1 pt per paddle)
• 1 pt - The scoring text is positioned and updated appropriately. The positioning need only approximate that in the video.
• 1 pt - The game includes a “Restart” button that resets the score and relaunches the ball.

Submission

# Implementation of classic arcade game Pong

import simplegui
import random

# initialize globals - pos and vel encode vertical info for paddles
WIDTH = 600
HEIGHT = 400       
BALL_RADIUS = 20
PAD_WIDTH = 8
PAD_HEIGHT = 80
HALF_PAD_WIDTH = PAD_WIDTH / 2
HALF_PAD_HEIGHT = PAD_HEIGHT / 2
LEFT = False
RIGHT = True

# initialize ball_pos and ball_vel for new bal in middle of table
# if direction is RIGHT, the ball's velocity is upper right, else upper left
def spawn_ball(direction):
    global ball_pos, ball_vel # these are vectors stored as lists
    ball_pos = [WIDTH / 2, HEIGHT / 2]
    ball_vel = [0, 0]
    ball_vel[0] = random.randrange(120, 240) / 60
    # ball should be upwards
    ball_vel[1] = - random.randrange(60, 180) / 60
    if not direction:
        ball_vel[0] = - ball_vel[0]

        
# define event handlers
def new_game():
    global paddle1_pos, paddle2_pos, paddle1_vel, paddle2_vel  # these are numbers
    global score1, score2  # these are ints
    paddle1_pos = HEIGHT / 2
    paddle2_pos = HEIGHT / 2
    paddle1_vel = 0
    paddle2_vel = 0    
    score1 = 0
    score2 = 0
        
    spawn_ball(random.choice([RIGHT, LEFT]))

    
# define canva    
def draw(canvas):
    global score1, score2, paddle1_pos, paddle2_pos, ball_pos, ball_vel
         
    # draw mid line and gutters
    canvas.draw_line([WIDTH / 2, 0],[WIDTH / 2, HEIGHT], 1, "White")
    canvas.draw_line([PAD_WIDTH + 0.5, 0],[PAD_WIDTH + 0.5, HEIGHT], 1, "White")
    canvas.draw_line([WIDTH - PAD_WIDTH - 0.5, 0],[WIDTH - PAD_WIDTH - 0.5, HEIGHT], 1, "White")
        
    # update ball
    ball_pos[0] += ball_vel[0]
    ball_pos[1] += ball_vel[1]
    
    # ball collides with the top and bottom walls
    if ball_pos[1] <= BALL_RADIUS:
        ball_vel[1] = - ball_vel[1]
    if ball_pos[1] >= HEIGHT - BALL_RADIUS:
        ball_vel[1] = - ball_vel[1]
            
    # draw ball
    canvas.draw_circle(ball_pos, BALL_RADIUS, 2, "Red", "White")
    
    # update paddle's vertical position, keep paddle on the screen
    global paddle1_vel, paddle2_vel
    if HEIGHT - HALF_PAD_HEIGHT >= paddle1_pos + paddle1_vel >= HALF_PAD_HEIGHT:
        paddle1_pos += paddle1_vel
    if HEIGHT - HALF_PAD_HEIGHT >= paddle2_pos + paddle2_vel >= HALF_PAD_HEIGHT:
        paddle2_pos += paddle2_vel
        
    # draw paddles
    canvas.draw_line([HALF_PAD_WIDTH, paddle1_pos + HALF_PAD_HEIGHT], 
                     [HALF_PAD_WIDTH, paddle1_pos - HALF_PAD_HEIGHT],
                     PAD_WIDTH, "Green")
    canvas.draw_line((WIDTH - HALF_PAD_WIDTH, paddle2_pos + HALF_PAD_HEIGHT),
                     (WIDTH - HALF_PAD_WIDTH, paddle2_pos - HALF_PAD_HEIGHT),
                     PAD_WIDTH, "Blue")
                         
    # determine whether paddle and ball collide    
    # ball hits the left gutter, right player gets 1 pt, respawn towards right
    if ball_pos[0] <= PAD_WIDTH + BALL_RADIUS:
        if (paddle1_pos - HALF_PAD_HEIGHT <= ball_pos[1] <= paddle1_pos + HALF_PAD_HEIGHT):
            ball_vel[0] = - ball_vel[0]
            # increase vel by 10% each time it strikes a paddle
            ball_vel[0] *= 1.1
            ball_vel[1] *= 1.1
        else:
            score2 += 1
            spawn_ball(RIGHT)
    
    # ball hits the right gutter, left player gets 1 pt, respawn towards left
    if ball_pos[0] >= WIDTH - PAD_WIDTH - BALL_RADIUS:
        if (paddle2_pos - HALF_PAD_HEIGHT <= ball_pos[1] <= paddle2_pos + HALF_PAD_HEIGHT):
            ball_vel[0] = - ball_vel[0]
            # increase vel by 10% each time it strikes a paddle
            ball_vel[0] *= 1.1
            ball_vel[1] *= 1.1
        else:
            score1 += 1
            spawn_ball(LEFT)
        
    # draw scores
    canvas.draw_text(str(score1), [100, 50], 40, "Red")
    canvas.draw_text(str(score2), [460, 50], 40, "Red")
    
    
    
def keydown(key):
    global paddle1_vel, paddle2_vel
    vel = 4
    if key == simplegui.KEY_MAP['w']:
        paddle1_vel -= vel
    if key == simplegui.KEY_MAP['s']:
        paddle1_vel += vel
    if key == simplegui.KEY_MAP['up']:
        paddle2_vel -= vel
    if key == simplegui.KEY_MAP['down']:
        paddle2_vel += vel

def keyup(key):
    global paddle1_vel, paddle2_vel
    if key == simplegui.KEY_MAP['w']:
        paddle1_vel = 0
    if key == simplegui.KEY_MAP['s']:
        paddle1_vel = 0
    if key == simplegui.KEY_MAP['up']:
        paddle2_vel = 0
    if key == simplegui.KEY_MAP['down']:
        paddle2_vel = 0

        
# create frame
frame = simplegui.create_frame("Pong", WIDTH, HEIGHT)
frame.set_draw_handler(draw)
frame.set_keydown_handler(keydown)
frame.set_keyup_handler(keyup)
frame.add_button("Restart", new_game, 100)


# start frame
new_game()
frame.start()