Snake game in PyGTK
last modified October 18, 2023
In this part of the PyGTK programming tutorial, we create a Snake game clone.
Snake game
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.
Development
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 = [0] * ALL_DOTS
y = [0] * 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[0] == self.apple_x and y[0] == 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[0] -= DOT_SIZE
if self.right:
x[0] += DOT_SIZE
if self.up:
y[0] -= DOT_SIZE
if self.down:
y[0] += DOT_SIZE
def check_collision(self):
z = self.dots
while z > 0:
if z > 4 and x[0] == x[z] and y[0] == y[z]:
self.inGame = False
z = z - 1
if y[0] > HEIGHT - DOT_SIZE:
self.inGame = False
if y[0] < 0:
self.inGame = False
if x[0] > WIDTH - DOT_SIZE:
self.inGame = False
if x[0] < 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 define some globals used in our game.
The WIDTH and 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.
The RAND_POS constant is used to calculate a random position of an apple.
The DELAY constant determines the speed of the game.
x = [0] * ALL_DOTS y = [0] * ALL_DOTS
These two lists store x, y coordinates of all possible joints of a snake.
The 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.
In the 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[0] -= DOT_SIZE
Move the head to the left.
In the checkCollision method, we determine if the snake has
hit itself or one of the walls.
while z > 0:
if z > 4 and x[0] == x[z] and y[0] == 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[0] > HEIGHT - DOT_SIZE:
self.inGame = False
We finish the game if the snake hits the bottom of the Board.
The 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.
In the 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 move
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.
