Mini-project # 4 - "Pong"

An Introduction to Interactive Programming in Python

Mini-project # 4 - "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 templates 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.

SOLUTION

# 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
ball_pos = [WIDTH/2,HEIGHT/2]
ball_vel = [-random.randrange(60, 180)/60,random.randrange(120, 240)/60]
paddle1_pos = HEIGHT/2
paddle2_pos = HEIGHT/2

# 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[1] = -random.randrange(60, 180)/60
    if direction == "RIGHT":
        ball_vel[0] = random.randrange(120, 240)/60
    else:
        ball_vel[0] = -random.randrange(120, 240)/60

# define event handlers
def new_game():
    global paddle1_pos, paddle2_pos, paddle1_vel, paddle2_vel 
    global score1, score2
    paddle1_pos = HEIGHT/2
    paddle2_pos = HEIGHT/2
    paddle1_vel = 0
    paddle2_vel = 0
    score1 = 0
    score2 = 0
    if random.randrange(0,11) % 2 == 0:
        spawn_ball("RIGHT")
    else:
        spawn_ball("LEFT")

def draw(canvas):
    global score1, score2, paddle1_vel, paddle2_vel, 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],[PAD_WIDTH, HEIGHT], 1, "White")
    canvas.draw_line([WIDTH - PAD_WIDTH, 0],[WIDTH - PAD_WIDTH, HEIGHT], 1, "White")
    
    # draw ball
    canvas.draw_circle(ball_pos, BALL_RADIUS, 2, "Red", "White")
    
    # draw paddles
    canvas.draw_polygon([(0, paddle1_pos - HALF_PAD_HEIGHT), (0, paddle1_pos + HALF_PAD_HEIGHT), (PAD_WIDTH - 2, paddle1_pos + HALF_PAD_HEIGHT), (PAD_WIDTH - 2, paddle1_pos - HALF_PAD_HEIGHT)], PAD_WIDTH - 1, "Green", "Green")
    canvas.draw_polygon([(WIDTH, paddle2_pos - HALF_PAD_HEIGHT), (WIDTH, paddle2_pos + HALF_PAD_HEIGHT), (WIDTH - PAD_WIDTH + 2, paddle2_pos + HALF_PAD_HEIGHT), (WIDTH - PAD_WIDTH + 2, paddle2_pos - HALF_PAD_HEIGHT)], PAD_WIDTH - 1, "Magenta", "Magenta")
    
    # draw scores
    canvas.draw_text(str(score1),[150, 40], 48, "Magenta")
    canvas.draw_text(str(score2),[450, 40], 48, "Green") 
    
    # update paddle's vertical position, keep paddle on the screen
    if paddle1_pos < (HALF_PAD_HEIGHT) and paddle1_vel < 0:
        paddle1_vel = 0
    if paddle2_pos < (HALF_PAD_HEIGHT) and paddle2_vel < 0:
        paddle2_vel = 0
    if paddle1_pos > (HEIGHT - (HALF_PAD_HEIGHT)) and paddle1_vel > 0:
        paddle1_vel = 0
    if paddle2_pos > (HEIGHT - (HALF_PAD_HEIGHT)) and paddle2_vel > 0:
        paddle2_vel = 0    
    paddle1_pos += paddle1_vel
    paddle2_pos += paddle2_vel        
    
    # update ball
    ball_pos[0] += ball_vel[0]
    ball_pos[1] += ball_vel[1]
    if ball_pos[1] >= (HEIGHT - BALL_RADIUS) or ball_pos[1] <= (BALL_RADIUS):
        ball_vel[1] = -ball_vel[1]
    if ball_pos[0] <= (PAD_WIDTH + BALL_RADIUS):
        if ball_pos[1] < (paddle1_pos - HALF_PAD_HEIGHT) or ball_pos[1] > (paddle1_pos + HALF_PAD_HEIGHT):
            spawn_ball("RIGHT")
            score2 += 1
        else:
            ball_vel[0] = -ball_vel[0] * 1.1
            
    if  ball_pos[0] >= (WIDTH - PAD_WIDTH - BALL_RADIUS):
        if ball_pos[1] < (paddle2_pos - HALF_PAD_HEIGHT) or ball_pos[1] > (paddle2_pos + HALF_PAD_HEIGHT):
            spawn_ball("LEFT")
            score1 += 1
        else:
            ball_vel[0] = -ball_vel[0] * 1.1
      
def keydown(key):
    global paddle1_vel, paddle2_vel
    if key == simplegui.KEY_MAP['w']:
        paddle1_vel = -4
    if key == simplegui.KEY_MAP['s']:
        paddle1_vel = 4
    if key == simplegui.KEY_MAP['up']:
        paddle2_vel = -4
    if key == simplegui.KEY_MAP['down']:
        paddle2_vel = 4
   
def keyup(key):
    global paddle1_vel, paddle2_vel
    if key == simplegui.KEY_MAP['w'] or key == simplegui.KEY_MAP['s']:
        paddle1_vel = 0
    if key == simplegui.KEY_MAP['up'] or 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()

The code reference (CodeSkulptor )

http://www.codeskulptor.org/#user30_rZxUigtS8z_1.py