Game Development using Python - Organized by CSEA

Now that you are a Python Ninja,

Let's use a library to build the game

We will use pygame

Otherwise, refer to this slide

Specifications of the game


Screen(Canvas)
    Width: 900
    Height: 600
    Color: Black
    
Ball
    Radius: 20
    Initial position: X=(width/2), Y=(height/2)
    Velocity: random value [Use random.choice() in form of (x, y)] 
    Color: Red
    
Pad
    Width: 10
    Height: 100
    Color: Green
    
Boundary for pad
    Color: White

Refer back to this while coding this later

Let's warm things up...


import pygame

# '#' symbol is used for comments

#always call this before using pygame functions
pygame.init()

Use this link to see the documentation of Pygame!

Documentations might be boring, but no better alternatives exist till date :/

Start with some colors


WHITE = (255,255,255)
RED = (255,255,0)
GREEN = (0,255,0)
BLACK = (0,0,0)

Colors are defined in RGB (Red, Green, Blue) format

Lets get our canvas ready


SCREEN_SIZE = SCREEN_WIDTH, SCREEN_HEIGHT = (900, 600)
screen = pygame.display.set_mode(SCREEN_SIZE)
screen.fill(BLACK)

pygame.display.set_mode() takes a tuple as an argument. That tuple is the width and height.

Moving Ahead with the Ball


ball_centre = (SCREEN_WIDTH/2, SCREEN_HEIGHT/2)
ball_radius = 20
ball = pygame.draw.circle(screen, RED, ball_centre, ball_radius)

pygame.draw.circle() takes in 4 arguments: canvas, color, position and radius

Understanding the math behind the pads

Coding the paddle

Conditional Statements

Enhancing the if-conditions


PADDLE_LENGTH = 100
PADDLE_WIDTH = 10

paddle_1_top = (4, (SCREEN_HEIGHT/2) - (PADDLE_LENGTH/2))
paddle_1_bottom = (4, (SCREEN_HEIGHT/2) + (PADDLE_LENGTH/2))

paddle1 = pygame.draw.line(screen, GREEN, paddle_1_top, paddle_1_bottom, PADDLE_WIDTH)

pygame.draw.line() has 4 mandatory arguments: screen, color, top position, bottom position and 1 optional argument: width

Write the code for paddle 2 and boundary lines

Run your python code... A new static game screen should load

To exit the game, go to terminal again and press Ctrl + C

Hopefully you have made a screen something that looks like this:

In case you don't have the file you made, here's the starter code for you :)

Click here to download the starter code

Say hi to Newton!!

Let's get the Physics of the game

Moving the objects


Ball
	Velocity: (x1, y1)
	Every few milliseconds the position of the ball
	changes by x1 units in X axis and y1 unit in Y axis

Paddle
	Velocity: (0, y2)
	Every keystroke the position of the paddle changes vertically

Some initial velocities:


ball_velocity = (1, random.choice(range(-10, 10)))
paddle1_velocity = (0,0)
paddle2_velocity = (0,0)

Let's make use of functions

Hope you know how to write functions


#function to calculate new position
def get_new_position(pos, vel):
	return (pos[0] + vel[0], pos[1] + vel[1]

Pay special attention to indentation and colon (:)

Let's change the position of the ball

Type this code inside the while loop


#ball_center changes based on the current ball_center 
#and ball velocity specified
ball_center = get_new_position(ball_center, ball_velocity)

#draw the new ball
ball = pygame.draw.circle(screen, RED, ball_center, BALL_RADIUS)

#update the changes on the screen
python.display.update()

Changing the position means changing the coordinates of the centre of the ball

How to train your dragon? :P

Moving Ahead ...

Controlling collisions


# Checking for bottom and top of the screen

if (ball_center[1]+BALL_RADIUS > SCREEN_HEIGHT 
	or ball_center[1]-BALL_RADIUS < 0):
		ball_velocity = (ball_velocity[0], -ball_velocity[1])

Taking care in the Y-axis

Moving Ahead ...

Controlling collisions


if (ball_center[0] + BALL_RADIUS > BOUNDARY_RIGHT_TOP[0] 
		or ball_center[0] - BALL_RADIUS < BOUNDARY_LEFT_TOP[0]):
		ball_velocity = (-ball_velocity[0], ball_velocity[1])

Taking care in the X-axis

BOUNDARY_LEFT_TOP and BOUNDARY_RIGHT_TOP are defined in the starter code

Simplicity of pygame

Events


Examples of Events:
	KEYDOWN
	KEYUP
	QUIT
	MOUSECLICK
	...

All these are inbuilt in Pygame :)

To know more about our events, click here :P

Capturing pygame events

pygame.event.get() -> Returns a list of events

Avoiding Ctrl + C

Activating the 'close' button of the window


for event in pygame.event.get():
		if event.type == pygame.QUIT:
			pygame.quit()
			sys.exit()

Doing things with keyboard

Let's make the paddle move


#.... Continued from if statement after pygame.QUIT
elif event.type == pygame.KEYDOWN:
	if event.key == pygame.K_UP:
		paddle2_velocity = (0, -1)
	elif event.key == pygame.K_DOWN:
		paddle2_velocity = (0,1)
	elif event.key == pygame.K_w:
		paddle1_velocity = (0, -1)
	elif event.key == pygame.K_s:
		paddle1_velocity = (0, 1)

Adding code for KEYUP


#... Continued from the elif statement after pygame.KEYDOWN
elif event.type == pygame.KEYUP:
	if event.key == pygame.K_UP or pygame.K_DOWN:
		paddle2_velocity = (0,0)
	#add KEYUP handler for paddle 1

Update paddle position


paddle2_top = get_new_position(paddle2_top, paddle2_velocity)
paddle2_bottom = get_new_position(paddle2_bottom, paddle2_velocity)

Note: We are using the same function that we made for the ball. Most important use of functions: reusability

Did you notice something?

Your paddle goes beyond the screen. Let's fix that!

Fixing the paddle

Modify the previous code


p2_new_top = get_new_position(paddle2_top, paddle2_velocity)
p2_new_bottom = get_new_position(paddle2_bottom, paddle2_velocity)

if (p2_new_top[1] > 0 and p2_new_bottom[1] < SCREEN_HEIGHT):
		paddle2_top = p2_new_top
		paddle2_bottom = p2_new_bottom

# Do the same for paddle 1

Bounding the statements by an if statement

A lot has been done...

Take a minute to revisit the slides

Now let's add interaction between the paddle and the ball

One final thing before the game can be played...

The ball talks to the paddle :D


if ball_center[0] + BALL_RADIUS > BOUNDARY_RIGHT_TOP[0]:
	if (paddle2_top[1] < ball_center[1] 
		and paddle2_bottom[1] > ball_center[1]):
		ball_velocity = (-ball_velocity[0], ball_velocity[1])
	else:
		ball_center = (SCREEN_WIDTH/2, SCREEN_HEIGHT/2)
		ball_velocity = (-1, random.choice(range(-10, 10)))

Compare your game with ours

Click here

There are few good coding practices we have followed :)

Our source of knowledge

Coursera

Introduction to Interactive Python

Udacity

Programming foundations with Python

Android Development for Beginners

MIT Open Course Ware

Linear Algebra (Mathematics) - Useful in 2nd semester

Show your running code to your friends and volunteers!

That's the complete game for you :)

Additional task : Add a score feature for both the players

If you have doubts, feel free to ask us. We are here to help you :)

Click here to five us a feedback. We will try to improve