Snake game in PyGTK
In this part of the PyGTK programming tutorial, we will create a Snake game clone.
Snake is an older classic video game. It was first created in late 70s. Later it was brought to PCs. In this game the player controls a snake. The objective is to eat as many apples as possible. Each time the snake eats an apple, its body grows. The snake must avoid the walls and its own body. This game is sometimes called Nibbles.
The size of each of the joints of a snake is 10px. The snake is controlled with the cursor keys. Initially the snake has three joints. The game starts immediately. If the game is finished, we display "Game Over" message in the middle of the Board.
#!/usr/bin/python # ZetCode PyGTK tutorial # # This is a simple snake game # clone # # author: jan bodnar # website: zetcode.com # last edited: February 2009 import sys import gtk import cairo import random import glib WIDTH = 300 HEIGHT = 270 DOT_SIZE = 10 ALL_DOTS = WIDTH * HEIGHT / (DOT_SIZE * DOT_SIZE) RAND_POS = 26 x =  * ALL_DOTS y =  * ALL_DOTS class Board(gtk.DrawingArea): def __init__(self): super(Board, self).__init__() self.modify_bg(gtk.STATE_NORMAL, gtk.gdk.Color(0, 0, 0)) self.set_size_request(WIDTH, HEIGHT) self.connect("expose-event", self.expose) self.init_game() def on_timer(self): if self.inGame: self.check_apple() self.check_collision() self.move() self.queue_draw() return True else: return False def init_game(self): self.left = False self.right = True self.up = False self.down = False self.inGame = True self.dots = 3 for i in range(self.dots): x[i] = 50 - i * 10 y[i] = 50 try: self.dot = cairo.ImageSurface.create_from_png("dot.png") self.head = cairo.ImageSurface.create_from_png("head.png") self.apple = cairo.ImageSurface.create_from_png("apple.png") except Exception, e: print e.message sys.exit(1) self.locate_apple() glib.timeout_add(100, self.on_timer) def expose(self, widget, event): cr = widget.window.cairo_create() if self.inGame: cr.set_source_rgb(0, 0, 0) cr.paint() cr.set_source_surface(self.apple, self.apple_x, self.apple_y) cr.paint() for z in range(self.dots): if (z == 0): cr.set_source_surface(self.head, x[z], y[z]) cr.paint() else: cr.set_source_surface(self.dot, x[z], y[z]) cr.paint() else: self.game_over(cr) def game_over(self, cr): w = self.allocation.width / 2 h = self.allocation.height / 2 (x, y, width, height, dx, dy) = cr.text_extents("Game Over") cr.set_source_rgb(65535, 65535, 65535) cr.move_to(w - width/2, h) cr.show_text("Game Over") self.inGame = False def check_apple(self): if x == self.apple_x and y == self.apple_y: self.dots = self.dots + 1 self.locate_apple() def move(self): z = self.dots while z > 0: x[z] = x[(z - 1)] y[z] = y[(z - 1)] z = z - 1 if self.left: x -= DOT_SIZE if self.right: x += DOT_SIZE if self.up: y -= DOT_SIZE if self.down: y += DOT_SIZE def check_collision(self): z = self.dots while z > 0: if z > 4 and x == x[z] and y == y[z]: self.inGame = False z = z - 1 if y > HEIGHT - DOT_SIZE: self.inGame = False if y < 0: self.inGame = False if x > WIDTH - DOT_SIZE: self.inGame = False if x < 0: self.inGame = False def locate_apple(self): r = random.randint(0, RAND_POS) self.apple_x = r * DOT_SIZE r = random.randint(0, RAND_POS) self.apple_y = r * DOT_SIZE def on_key_down(self, event): key = event.keyval if key == gtk.keysyms.Left and not self.right: self.left = True self.up = False self.down = False if key == gtk.keysyms.Right and not self.left: self.right = True self.up = False self.down = False if key == gtk.keysyms.Up and not self.down: self.up = True self.right = False self.left = False if key == gtk.keysyms.Down and not self.up: self.down = True self.right = False self.left = False class Snake(gtk.Window): def __init__(self): super(Snake, self).__init__() self.set_title('Snake') self.set_size_request(WIDTH, HEIGHT) self.set_resizable(False) self.set_position(gtk.WIN_POS_CENTER) self.board = Board() self.connect("key-press-event", self.on_key_down) self.add(self.board) self.connect("destroy", gtk.main_quit) self.show_all() def on_key_down(self, widget, event): key = event.keyval self.board.on_key_down(event) Snake() gtk.main()
First we will define some globals used in our game.
HEIGHT constants determine
the size of the Board. The
DOT_SIZE is the size of the apple and the dot
of the snake. The
ALL_DOTS constant defines the maximum number of
possible dots on the Board.
RAND_POS constant is used to calculate a random position of an apple.
DELAY constant determines the speed of the game.
x =  * ALL_DOTS y =  * ALL_DOTS
These two lists store x, y coordinates of all possible joints of a snake.
init_game() method initialises variables, loads
images and starts a timeout function.
self.left = False self.right = True self.up = False self.down = False self.inGame = True self.dots = 3
When the game starts, the snake has three joints. And it is heading to the right.
move() method we have the key algorithm of the game.
To understand it, look at how the snakeis moving. You control the head of the snake.
You can change its direction with the cursor keys. The rest of the joints move
one position up the chain. The second joint moves where the first was,
the third joint where the second was etc.
while z > 0: x[z] = x[(z - 1)] y[z] = y[(z - 1)] z = z - 1
This code moves the joints up the chain.
if self.left: x -= DOT_SIZE
Move the head to the left.
checkCollision() method, we determine if the snake has
hit itself or one of the walls.
while z > 0: if z > 4 and x == x[z] and y == y[z]: self.inGame = False z = z - 1
We finish the game if the snake hits one of its joints with the head.
if y > HEIGHT - DOT_SIZE: self.inGame = False
We finish the game if the snake hits the bottom of the Board.
locate_apple() method locates an apple randomly
on the form.
r = random.randint(0, RAND_POS)
We get a random number from 0 to RAND_POS - 1.
self.apple_x = r * DOT_SIZE ... self.apple_y = r * DOT_SIZE
These line set the x, y coordinates of the apple object.
self.connect("key-press-event", self.on_key_down) ... def on_key_down(self, widget, event): key = event.keyval self.board.on_key_down(event)
We catch the key press event in the Snake class, and delegate the processing to the board object.
on_key_dow() method of the Board class, we
determine which keys the player hit.
if key == gtk.keysyms.Left and not self.right: self.left = True self.up = False self.down = False
If we hit the left cursor key, we set
self.left variable to
True. This variable is used in the
method to change coordinates of the snake object. Notice also that
when the snake is heading to the right, we cannot turn immediately
to the left.
This was the Snake computer game programmed using PyGTK programming library.