Today I will ramble about game development with python . Python is very easy to learn and it is a very easy to prototype games with python. Pygame is a SDL binding fo python , visit pygame.org for more details.
2D Game Development Concepts
Sprites : Sprites are moveable game entities , I bet all of you have played super mario. The mario character you control is basically a sprite .
Game Loop : Game is loop is very common in most of the games , it something of this form( C is psuedo code )
while ( not_game_over)
{
if ( an_event_occurred )
handle_event()
}
Collision detection : In a game you often need to find out when you characters collide , this is called collision detection. There are many ways to perform collision detection. The easiest way is to define a bounding rectangle for the sprite and determine when these two rectangles overlap .
Input handling : While programming your game , you need to determine what needs to be done when user press the keyboard or mouse . With newer operating system this is way too easy you just need to use the services provided by the operating system . Back in the good old days of DOS this was not the case , you need to write a separate keyboard handler , mouse handler etc so that your game responds well.
Sound and Music : You also need to play sound for special game events , eg a sound when you won the game etc
Handling game states : Each game entity and the game itself maintains a state and actions need to be performed based on the current state of the game. One crude way to handle states is to use an enumeration. But when the number of states increase they become very cumbersome to mange. A better way is to use a variation of the state pattern
I am too lazy to write my own game now , i am therefore copy pasting the example games provided by the pygame itself 🙂 . They are well commented and easy to understand
Getting started with pygame
your first pgame program
[sourcecode language=”python”]
import pygame
pygame.init();
dimensions = ( 640 , 480 )
color_red = ( 255 , 0 , 0 )
screen = pygame.display.set_mode(dimensions)
pygame.display.set_caption("Pygame Template")
game_running = True
clock = pygame.time.Clock()
while game_running == True:
for event in pygame.event.get():
if event.type == pygame.QUIT:
game_running = False
screen.fill(color_red)
pygame.display.flip();
clock.tick(20)
pygame.quit()
[/sourcecode]
Chimp line by line example
[sourcecode language=”python”]
#!/usr/bin/env python
"""
This simple example is used for the line-by-line tutorial
that comes with pygame. It is based on a ‘popular’ web banner.
Note there are comments here, but for the full explanation,
follow along in the tutorial.
"""
#Import Modules
import os, pygame
from pygame.locals import *
from pygame.compat import geterror
if not pygame.font: print (‘Warning, fonts disabled’)
if not pygame.mixer: print (‘Warning, sound disabled’)
main_dir = os.path.split(os.path.abspath(__file__))[0]
data_dir = os.path.join(main_dir, ‘data’)
#functions to create our resources
def load_image(name, colorkey=None):
fullname = os.path.join(data_dir, name)
try:
image = pygame.image.load(fullname)
except pygame.error:
print (‘Cannot load image:’, fullname)
raise SystemExit(str(geterror()))
image = image.convert()
if colorkey is not None:
if colorkey is -1:
colorkey = image.get_at((0,0))
image.set_colorkey(colorkey, RLEACCEL)
return image, image.get_rect()
def load_sound(name):
class NoneSound:
def play(self): pass
if not pygame.mixer or not pygame.mixer.get_init():
return NoneSound()
fullname = os.path.join(data_dir, name)
try:
sound = pygame.mixer.Sound(fullname)
except pygame.error:
print (‘Cannot load sound: %s’ % fullname)
raise SystemExit(str(geterror()))
return sound
#classes for our game objects
class Fist(pygame.sprite.Sprite):
"""moves a clenched fist on the screen, following the mouse"""
def __init__(self):
pygame.sprite.Sprite.__init__(self) #call Sprite initializer
self.image, self.rect = load_image(‘fist.bmp’, -1)
self.punching = 0
def update(self):
"move the fist based on the mouse position"
pos = pygame.mouse.get_pos()
self.rect.midtop = pos
if self.punching:
self.rect.move_ip(5, 10)
def punch(self, target):
"returns true if the fist collides with the target"
if not self.punching:
self.punching = 1
hitbox = self.rect.inflate(-5, -5)
return hitbox.colliderect(target.rect)
def unpunch(self):
"called to pull the fist back"
self.punching = 0
class Chimp(pygame.sprite.Sprite):
"""moves a monkey critter across the screen. it can spin the
monkey when it is punched."""
def __init__(self):
pygame.sprite.Sprite.__init__(self) #call Sprite intializer
self.image, self.rect = load_image(‘chimp.bmp’, -1)
screen = pygame.display.get_surface()
self.area = screen.get_rect()
self.rect.topleft = 10, 10
self.move = 9
self.dizzy = 0
def update(self):
"walk or spin, depending on the monkeys state"
if self.dizzy:
self._spin()
else:
self._walk()
def _walk(self):
"move the monkey across the screen, and turn at the ends"
newpos = self.rect.move((self.move, 0))
if self.rect.left < self.area.left or \
self.rect.right > self.area.right:
self.move = -self.move
newpos = self.rect.move((self.move, 0))
self.image = pygame.transform.flip(self.image, 1, 0)
self.rect = newpos
def _spin(self):
"spin the monkey image"
center = self.rect.center
self.dizzy = self.dizzy + 12
if self.dizzy >= 360:
self.dizzy = 0
self.image = self.original
else:
rotate = pygame.transform.rotate
self.image = rotate(self.original, self.dizzy)
self.rect = self.image.get_rect(center=center)
def punched(self):
"this will cause the monkey to start spinning"
if not self.dizzy:
self.dizzy = 1
self.original = self.image
def main():
"""this function is called when the program starts.
it initializes everything it needs, then runs in
a loop until the function returns."""
#Initialize Everything
pygame.init()
screen = pygame.display.set_mode((468, 60))
pygame.display.set_caption(‘Monkey Fever’)
pygame.mouse.set_visible(0)
#Create The Backgound
background = pygame.Surface(screen.get_size())
background = background.convert()
background.fill((250, 250, 250))
#Put Text On The Background, Centered
if pygame.font:
font = pygame.font.Font(None, 36)
text = font.render("Pummel The Chimp, And Win $$$", 1, (10, 10, 10))
textpos = text.get_rect(centerx=background.get_width()/2)
background.blit(text, textpos)
#Display The Background
screen.blit(background, (0, 0))
pygame.display.flip()
#Prepare Game Objects
clock = pygame.time.Clock()
whiff_sound = load_sound(‘whiff.wav’)
punch_sound = load_sound(‘punch.wav’)
chimp = Chimp()
fist = Fist()
allsprites = pygame.sprite.RenderPlain((fist, chimp))
#Main Loop
going = True
while going:
clock.tick(60)
#Handle Input Events
for event in pygame.event.get():
if event.type == QUIT:
going = False
elif event.type == KEYDOWN and event.key == K_ESCAPE:
going = False
elif event.type == MOUSEBUTTONDOWN:
if fist.punch(chimp):
punch_sound.play() #punch
chimp.punched()
else:
whiff_sound.play() #miss
elif event.type == MOUSEBUTTONUP:
fist.unpunch()
allsprites.update()
#Draw Everything
screen.blit(background, (0, 0))
allsprites.draw(screen)
pygame.display.flip()
pygame.quit()
#Game Over
#this calls the ‘main’ function when this script is executed
if __name__ == ‘__main__’:
main()
[/sourcecode]
The aliens example
[sourcecode language=”python”]
#!/usr/bin/env python
import random, os.path
#import basic pygame modules
import pygame
from pygame.locals import *
#see if we can load more than standard BMP
if not pygame.image.get_extended():
raise SystemExit("Sorry, extended image module required")
#game constants
MAX_SHOTS = 2 #most player bullets onscreen
ALIEN_ODDS = 22 #chances a new alien appears
BOMB_ODDS = 60 #chances a new bomb will drop
ALIEN_RELOAD = 12 #frames between new aliens
SCREENRECT = Rect(0, 0, 640, 480)
SCORE = 0
main_dir = os.path.split(os.path.abspath(__file__))[0]
def load_image(file):
"loads an image, prepares it for play"
file = os.path.join(main_dir, ‘data’, file)
try:
surface = pygame.image.load(file)
except pygame.error:
raise SystemExit(‘Could not load image "%s" %s’%(file, pygame.get_error()))
return surface.convert()
def load_images(*files):
imgs = []
for file in files:
imgs.append(load_image(file))
return imgs
class dummysound:
def play(self): pass
def load_sound(file):
if not pygame.mixer: return dummysound()
file = os.path.join(main_dir, ‘data’, file)
try:
sound = pygame.mixer.Sound(file)
return sound
except pygame.error:
print (‘Warning, unable to load, %s’ % file)
return dummysound()
# each type of game object gets an init and an
# update function. the update function is called
# once per frame, and it is when each object should
# change it’s current position and state. the Player
# object actually gets a "move" function instead of
# update, since it is passed extra information about
# the keyboard
class Player(pygame.sprite.Sprite):
speed = 10
bounce = 24
gun_offset = -11
images = []
def __init__(self):
pygame.sprite.Sprite.__init__(self, self.containers)
self.image = self.images[0]
self.rect = self.image.get_rect(midbottom=SCREENRECT.midbottom)
self.reloading = 0
self.origtop = self.rect.top
self.facing = -1
def move(self, direction):
if direction: self.facing = direction
self.rect.move_ip(direction*self.speed, 0)
self.rect = self.rect.clamp(SCREENRECT)
if direction < 0:
self.image = self.images[0]
elif direction > 0:
self.image = self.images[1]
self.rect.top = self.origtop – (self.rect.left//self.bounce%2)
def gunpos(self):
pos = self.facing*self.gun_offset + self.rect.centerx
return pos, self.rect.top
class Alien(pygame.sprite.Sprite):
speed = 13
animcycle = 12
images = []
def __init__(self):
pygame.sprite.Sprite.__init__(self, self.containers)
self.image = self.images[0]
self.rect = self.image.get_rect()
self.facing = random.choice((-1,1)) * Alien.speed
self.frame = 0
if self.facing < 0:
self.rect.right = SCREENRECT.right
def update(self):
self.rect.move_ip(self.facing, 0)
if not SCREENRECT.contains(self.rect):
self.facing = -self.facing;
self.rect.top = self.rect.bottom + 1
self.rect = self.rect.clamp(SCREENRECT)
self.frame = self.frame + 1
self.image = self.images[self.frame//self.animcycle%3]
class Explosion(pygame.sprite.Sprite):
defaultlife = 12
animcycle = 3
images = []
def __init__(self, actor):
pygame.sprite.Sprite.__init__(self, self.containers)
self.image = self.images[0]
self.rect = self.image.get_rect(center=actor.rect.center)
self.life = self.defaultlife
def update(self):
self.life = self.life – 1
self.image = self.images[self.life//self.animcycle%2]
if self.life <= 0: self.kill()
class Shot(pygame.sprite.Sprite):
speed = -11
images = []
def __init__(self, pos):
pygame.sprite.Sprite.__init__(self, self.containers)
self.image = self.images[0]
self.rect = self.image.get_rect(midbottom=pos)
def update(self):
self.rect.move_ip(0, self.speed)
if self.rect.top <= 0:
self.kill()
class Bomb(pygame.sprite.Sprite):
speed = 9
images = []
def __init__(self, alien):
pygame.sprite.Sprite.__init__(self, self.containers)
self.image = self.images[0]
self.rect = self.image.get_rect(midbottom=
alien.rect.move(0,5).midbottom)
def update(self):
self.rect.move_ip(0, self.speed)
if self.rect.bottom >= 470:
Explosion(self)
self.kill()
class Score(pygame.sprite.Sprite):
def __init__(self):
pygame.sprite.Sprite.__init__(self)
self.font = pygame.font.Font(None, 20)
self.font.set_italic(1)
self.color = Color(‘white’)
self.lastscore = -1
self.update()
self.rect = self.image.get_rect().move(10, 450)
def update(self):
if SCORE != self.lastscore:
self.lastscore = SCORE
msg = "Score: %d" % SCORE
self.image = self.font.render(msg, 0, self.color)
def main(winstyle = 0):
# Initialize pygame
pygame.init()
if pygame.mixer and not pygame.mixer.get_init():
print (‘Warning, no sound’)
pygame.mixer = None
# Set the display mode
winstyle = 0 # |FULLSCREEN
bestdepth = pygame.display.mode_ok(SCREENRECT.size, winstyle, 32)
screen = pygame.display.set_mode(SCREENRECT.size, winstyle, bestdepth)
#Load images, assign to sprite classes
#(do this before the classes are used, after screen setup)
img = load_image(‘player1.gif’)
Player.images = [img, pygame.transform.flip(img, 1, 0)]
img = load_image(‘explosion1.gif’)
Explosion.images = [img, pygame.transform.flip(img, 1, 1)]
Alien.images = load_images(‘alien1.gif’, ‘alien2.gif’, ‘alien3.gif’)
Bomb.images = [load_image(‘bomb.gif’)]
Shot.images = [load_image(‘shot.gif’)]
#decorate the game window
icon = pygame.transform.scale(Alien.images[0], (32, 32))
pygame.display.set_icon(icon)
pygame.display.set_caption(‘Pygame Aliens’)
pygame.mouse.set_visible(0)
#create the background, tile the bgd image
bgdtile = load_image(‘background.gif’)
background = pygame.Surface(SCREENRECT.size)
for x in range(0, SCREENRECT.width, bgdtile.get_width()):
background.blit(bgdtile, (x, 0))
screen.blit(background, (0,0))
pygame.display.flip()
#load the sound effects
boom_sound = load_sound(‘boom.wav’)
shoot_sound = load_sound(‘car_door.wav’)
if pygame.mixer:
music = os.path.join(main_dir, ‘data’, ‘house_lo.wav’)
pygame.mixer.music.load(music)
pygame.mixer.music.play(-1)
# Initialize Game Groups
aliens = pygame.sprite.Group()
shots = pygame.sprite.Group()
bombs = pygame.sprite.Group()
all = pygame.sprite.RenderUpdates()
lastalien = pygame.sprite.GroupSingle()
#assign default groups to each sprite class
Player.containers = all
Alien.containers = aliens, all, lastalien
Shot.containers = shots, all
Bomb.containers = bombs, all
Explosion.containers = all
Score.containers = all
#Create Some Starting Values
global score
alienreload = ALIEN_RELOAD
kills = 0
clock = pygame.time.Clock()
#initialize our starting sprites
global SCORE
player = Player()
Alien() #note, this ‘lives’ because it goes into a sprite group
if pygame.font:
all.add(Score())
while player.alive():
#get input
for event in pygame.event.get():
if event.type == QUIT or \
(event.type == KEYDOWN and event.key == K_ESCAPE):
return
keystate = pygame.key.get_pressed()
# clear/erase the last drawn sprites
all.clear(screen, background)
#update all the sprites
all.update()
#handle player input
direction = keystate[K_RIGHT] – keystate[K_LEFT]
player.move(direction)
firing = keystate[K_SPACE]
if not player.reloading and firing and len(shots) < MAX_SHOTS:
Shot(player.gunpos())
shoot_sound.play()
player.reloading = firing
# Create new alien
if alienreload:
alienreload = alienreload – 1
elif not int(random.random() * ALIEN_ODDS):
Alien()
alienreload = ALIEN_RELOAD
# Drop bombs
if lastalien and not int(random.random() * BOMB_ODDS):
Bomb(lastalien.sprite)
# Detect collisions
for alien in pygame.sprite.spritecollide(player, aliens, 1):
boom_sound.play()
Explosion(alien)
Explosion(player)
SCORE = SCORE + 1
player.kill()
for alien in pygame.sprite.groupcollide(shots, aliens, 1, 1).keys():
boom_sound.play()
Explosion(alien)
SCORE = SCORE + 1
for bomb in pygame.sprite.spritecollide(player, bombs, 1):
boom_sound.play()
Explosion(player)
Explosion(bomb)
player.kill()
#draw the scene
dirty = all.draw(screen)
pygame.display.update(dirty)
#cap the framerate
clock.tick(40)
if pygame.mixer:
pygame.mixer.music.fadeout(1000)
pygame.time.wait(1000)
pygame.quit()
#call the "main" function if running this script
if __name__ == ‘__main__’: main()
[/sourcecode]