Introduction to Game Programming Tutorial

Game Programming
LCA 2010
Richard Jones

The Basics
• Displaying something
• Controlling animation
• User input
• Gameplay mechanics
• Playing sound effects and music
• Further stuff

Displaying Something

• Opening a window
• Reading images
• Displaying images

Controlling Animation

• Image position on screen
• Updates over time
• Accounting for frame rate

User Input

• Getting events
• Distinct keyboard events vs. keyboard state

Gameplay Mechanics

• Interaction of game objects
• Detecting important events (game won or
game over)

Detecting Collisions

• Pixel-Perfect
• Axis-Aligned Bounding Box
• Circle-Circle
• Hash Map

Sound

• Reading sound ﬁles
• Playing sounds and background music

Opening a Window

import pyglet

w = pyglet.window.Window()

pyglet.app.run()

Clearing the Window
import pyglet


@w.event
def on_draw():
w.clear()

pyglet.app.run()

Drawing
import pyglet


ship_image = pyglet.image.load('data/ship.png')

@w.event
def on_draw():
w.clear()
ship_image.blit(100, 100)

pyglet.app.run()

Better Drawing
import pyglet


ship = pyglet.sprite.Sprite(ship_image)
ship.position = (100, 100)

@w.event
def on_draw():
w.clear()
ship_image.blit(100, 100)
ship.draw()

pyglet.app.run()

Animation
...
w.clear()
ship.draw()

def update(dt):
ship.x += 1

pyglet.clock.schedule_interval(update, 1./30)

pyglet.app.run()

Better Animation
...
w.clear()
ship.draw()

def update(dt):
ship.x += 1
ship.x += 100 * dt


pyglet.app.run()

Adding Asteroids
import random
import pyglet


def center_anchor(img):
img.anchor_x = img.width / 2
img.anchor_y = img.height / 2

...

Adding Asteroids
...
center_anchor(ship_image)

big_asteroid_image = pyglet.image.load('data/big_asteroid.png')
center_anchor(big_asteroid_image)
asteroids = []
for i in range(3):
x = random.randint(0, w.width)
y = random.randint(0, w.height)
s = pyglet.sprite.Sprite(big_asteroid_image, x, y)
s.dx = random.randint(-100, 100)
s.dy = random.randint(-100, 100)
asteroids.append(s)

@w.event
...

Adding Asteroids

...
@w.event
def on_draw():
w.clear()
for asteroid in asteroids:
asteroid.draw()
ship.draw()
...

Adding Asteroids

...
def update(dt):
ship.x += 100 * dt
asteroid.x += asteroid.dx*dt
asteroid.y += asteroid.dy*dt
...

A Little Refactoring

...
ship.dx = 100
ship.dy = 0

...

Screen Wrapping
...
def update(dt):
ship.x += 100 * dt
asteroid.x += asteroid.dx*dt
asteroid.y += asteroid.dy*dt
for a in asteroids + [ship]:
a.x += a.dx*dt
a.y += a.dy*dt
if a.x - a.width/2 > w.width:
a.x -= w.width + a.width
elif a.x + a.width/2 < 0:
a.x += w.width + a.width
if a.y - a.height/2 > w.height:
a.y -= w.height + a.height
elif a.y + a.height/2 < 0:
a.y += w.height + a.height
...

Control

import math
import random
import pyglet


...

Control
...
keys = pyglet.window.key.KeyStateHandler()
w.push_handlers(keys)

def update(dt):
if keys[pyglet.window.key.LEFT]:
ship.rotation -= 360*dt
if keys[pyglet.window.key.RIGHT]:
ship.rotation += 360*dt
rotation = math.radians(ship.rotation)
rotation_x = math.cos(-rotation)
rotation_y = math.sin(-rotation)
if keys[pyglet.window.key.UP]:
ship.dx += 200 * rotation_x * dt
ship.dy += 200 * rotation_y * dt

...

Rotation

...
ship.dx = 100
ship.dy = 0
ship.position = (w.width/2, w.height/2)
ship.dx = ship.dy = ship.dr = 0

...

Rotation

...
s = pyglet.sprite.Sprite(big_asteroid_image, x, y)
s.dx = random.randint(-100, 100)
s.dy = random.randint(-100, 100)
s.dr = random.randint(-100, 100)
asteroids.append(s)

...

Rotation
...
def update(dt):
if keys[pyglet.window.key.LEFT]:
ship.rotation -= 360*dt
if keys[pyglet.window.key.RIGHT]:
ship.rotation += 360*dt
ship.dr = (keys[pyglet.window.key.RIGHT] - keys[pyglet.window.key.LEFT]) * 360
rotation = math.pi * ship.rotation / 180.0
...
a.x += a.dx*dt
a.y += a.dy*dt
a.rotation += a.dr * dt
if a.x - a.width/2 > w.width:
a.x -= w.width + a.width

Collision Detection

distance

Collision Detection

import sys
import math
import random
import pyglet

...

Collision Detection

...
w.push_handlers(keys)

def distance(a, b):
return math.sqrt((a.x-b.x)**2 + (a.y-b.y)**2)

def update(dt):
...

Collision Detection

...

for a in asteroids:
if distance(a, ship) < (a.width/2 + ship.width/2):
sys.exit('GAME OVER')

...

Shooting

ship.position = (w.width/2, w.height/2)
ship.dx = ship.dy = ship.dr = 0
ship.gun_cooldown = 0

bullet_image = pyglet.image.load('data/bullet.png')
center_anchor(bullet_image)
bullets = []

...

...
Shooting
ship.dy += 200 * rotation_y * dt

if ship.gun_cooldown:
ship.gun_cooldown = max(0, ship.gun_cooldown - dt)
elif keys[pyglet.window.key.SPACE] and len(bullets) < 2:
b = pyglet.sprite.Sprite(bullet_image, ship.x, ship.y)
b.dx = rotation_x * 500
b.dy = rotation_y * 500
b.dr = 0
b.life = 1
bullets.append(b)
ship.gun_cooldown = .5

for b in list(bullets):
b.life -= dt
if b.life < 0:
bullets.remove(b)

for a in asteroids + [ship] + bullets:
a.x += a.dx*dt
...

Shooting

...
@w.event
def on_draw():
w.clear()
asteroid.draw()
for s in asteroids + bullets:
s.draw()
ship.draw()
...

Shooting ... and Hitting

...
def distance(a, b):
return math.sqrt((a.x-b.x)**2 + (a.y-b.y)**2)
def collide(a, b):
return distance(a, b) < (a.width/2 + b.width/2)
...

Shooting ... and Hitting
...

for a in asteroids:
if distance(a, ship) < (a.width/2 + ship.width/2):
for a in list(asteroids):
if collide(a, ship):
if collide(a, b):
bullets.remove(b)
asteroids.remove(a)

if not asteroids:
sys.exit('YOU WIN')

...

Chunks

...
center_anchor(bullet_image)
bullets = []

small_asteroid_image = pyglet.image.load('data/small_asteroid.png')
center_anchor(small_asteroid_image)
medium_asteroid_image = pyglet.image.load('data/medium_asteroid.png')
center_anchor(medium_asteroid_image)
big_asteroid_image = pyglet.image.load('data/big_asteroid.png')
center_anchor(big_asteroid_image)
...

...
Chunks
if collide(a, b):
bullets.remove(b)
asteroids.remove(a)
if a.image is big_asteroid_image.texture:
for i in range(2):
s = pyglet.sprite.Sprite(medium_asteroid_image, a.x, a.y)
s.dx = a.dx + random.randint(-50, 50)
s.dy = a.dy + random.randint(-50, 50)
s.dr = a.dr + random.randint(-50, 50)
asteroids.append(s)
elif a.image is medium_asteroid_image.texture:
for i in range(2):
s = pyglet.sprite.Sprite(small_asteroid_image, a.x, a.y)
s.dx = a.dx + random.randint(-50, 50)
s.dy = a.dy + random.randint(-50, 50)
s.dr = a.dr + random.randint(-50, 50)
asteroids.append(s)

if not asteroids:
sys.exit('YOU WIN')
...

Sound Effects

...
asteroids.append(s)

explosion_sound = pyglet.media.load('data/explosion.wav', streaming=False)
bullet_sound = pyglet.media.load('data/bullet.wav', streaming=False)

@w.event
def on_draw():
...

Sound Effects

...
bullets.append(b)
ship.gun_cooldown = .5
bullet_sound.play()

...

Sound Effects

...
bullets.remove(b)
asteroids.remove(a)
explosion_sound.play()
if a.image is big_asteroid_image.texture:

Further Stuff

• Opening screen
• Options menu
• Game won / game over screen
• Special effects

Other screen / menu

• Use libraries like Cocos2d (Scenes, Layers,
Sprites, Animations)

Special Effects

• Simple image animations
• Use libraries like lepton

Where To From Here?

• http://pyglet.org
• http://pygame.org
• http://los-cocos.org
• http://inventwithpython.com/
• http://pyweek.org

Introduction to Game Programming Tutorial

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