Snake AI in Pygame


In this article we will show you how to create basic game AI.

Adding the computer player:
We extend the code with a new class called Computer which will be our computer player. This contains routines to draw and move the computer snake.

class Computer:
    x = [0]
    y = [0]
    step = 44
    direction = 0
    length = 3
 
    updateCountMax = 2
    updateCount = 0
 
    def __init__(self, length):
       self.length = length
       for i in range(0,2000):
           self.x.append(-100)
           self.y.append(-100)
 
       # initial positions, no collision.
       self.x[0] = 1*44
       self.y[0] = 4*44
 
    def update(self):
 
        self.updateCount = self.updateCount + 1
        if self.updateCount > self.updateCountMax:
 
            # update previous positions
            for i in range(self.length-1,0,-1):
                self.x[i] = self.x[i-1]
                self.y[i] = self.y[i-1]
 
            # update position of head of snake
            if self.direction == 0:
                self.x[0] = self.x[0] + self.step
            if self.direction == 1:
                self.x[0] = self.x[0] - self.step
            if self.direction == 2:
                self.y[0] = self.y[0] - self.step
            if self.direction == 3:
                self.y[0] = self.y[0] + self.step
 
            self.updateCount = 0
 
 
    def moveRight(self):
        self.direction = 0
 
    def moveLeft(self):
        self.direction = 1
 
    def moveUp(self):
        self.direction = 2
 
    def moveDown(self):
        self.direction = 3 
 
    def draw(self, surface, image):
        for i in range(0,self.length):
            surface.blit(image,(self.x[i],self.y[i]))

We then call the update and drawing method of the computer.

    def on_loop(self):
        self.player.update()
        self.computer.update()
 
....
 
    def on_render(self):
        self._display_surf.fill((0,0,0))
        self.player.draw(self._display_surf, self._image_surf)
        self.apple.draw(self._display_surf, self._apple_surf)
        self.computer.draw(self._display_surf, self._image_surf)
        pygame.display.flip()

This will make the computer snake move and be drawn on the screen. It has the same properties as the human player.

Adding the intelligence to the computer player
Because this is a simple game, we do not need to create a complete thinking machine inside the game.  We simply need some basic  intelligence exhibited by our computer player.  Intelligence in games is often quite limited because most of the time more complexity is not neccesary or there simply is not the time available to implement clever algorithms.

The algorithm we will add will simply go to the destination. It will neglect any obstacles (the human player).

    def target(self,dx,dy):
        if self.x[0] > dx:
            self.moveLeft()
 
        if self.x[0] < dx:
            self.moveRight()
 
        if self.x[0] == dx:
            if self.y[0] < dy:
                self.moveDown()
 
            if self.y[0] > dy:
                self.moveUp()

Complete code
We end up with this complete code:

from pygame.locals import *
from random import randint
import pygame
import time
 
class Apple:
    x = 0
    y = 0
    step = 44
 
    def __init__(self,x,y):
        self.x = x * self.step
        self.y = y * self.step
 
    def draw(self, surface, image):
        surface.blit(image,(self.x, self.y)) 
 
 
class Player:
    x = [0]
    y = [0]
    step = 44
    direction = 0
    length = 3
 
    updateCountMax = 2
    updateCount = 0
 
    def __init__(self, length):
       self.length = length
       for i in range(0,2000):
           self.x.append(-100)
           self.y.append(-100)
 
       # initial positions, no collision.
       self.x[0] = 1*44
       self.x[0] = 2*44
 
    def update(self):
 
        self.updateCount = self.updateCount + 1
        if self.updateCount > self.updateCountMax:
 
            # update previous positions
            for i in range(self.length-1,0,-1):
                self.x[i] = self.x[i-1]
                self.y[i] = self.y[i-1]
 
            # update position of head of snake
            if self.direction == 0:
                self.x[0] = self.x[0] + self.step
            if self.direction == 1:
                self.x[0] = self.x[0] - self.step
            if self.direction == 2:
                self.y[0] = self.y[0] - self.step
            if self.direction == 3:
                self.y[0] = self.y[0] + self.step
 
            self.updateCount = 0
 
 
    def moveRight(self):
        self.direction = 0
 
    def moveLeft(self):
        self.direction = 1
 
    def moveUp(self):
        self.direction = 2
 
    def moveDown(self):
        self.direction = 3 
 
    def draw(self, surface, image):
        for i in range(0,self.length):
            surface.blit(image,(self.x[i],self.y[i])) 
 
 
 
class Computer:
    x = [0]
    y = [0]
    step = 44
    direction = 0
    length = 3
 
    updateCountMax = 2
    updateCount = 0
 
    def __init__(self, length):
       self.length = length
       for i in range(0,2000):
           self.x.append(-100)
           self.y.append(-100)
 
       # initial positions, no collision.
       self.x[0] = 1*44
       self.y[0] = 4*44
 
    def update(self):
 
        self.updateCount = self.updateCount + 1
        if self.updateCount > self.updateCountMax:
 
            # update previous positions
            for i in range(self.length-1,0,-1):
                self.x[i] = self.x[i-1]
                self.y[i] = self.y[i-1]
 
            # update position of head of snake
            if self.direction == 0:
                self.x[0] = self.x[0] + self.step
            if self.direction == 1:
                self.x[0] = self.x[0] - self.step
            if self.direction == 2:
                self.y[0] = self.y[0] - self.step
            if self.direction == 3:
                self.y[0] = self.y[0] + self.step
 
            self.updateCount = 0
 
 
    def moveRight(self):
        self.direction = 0
 
    def moveLeft(self):
        self.direction = 1
 
    def moveUp(self):
        self.direction = 2
 
    def moveDown(self):
        self.direction = 3 
 
 
    def target(self,dx,dy):
        if self.x[0] > dx:
            self.moveLeft()
 
        if self.x[0] < dx:
            self.moveRight()
 
        if self.x[0] == dx:
            if self.y[0] < dy:
                self.moveDown()
 
            if self.y[0] > dy:
                self.moveUp()
 
    def draw(self, surface, image):
        for i in range(0,self.length):
            surface.blit(image,(self.x[i],self.y[i])) 
 
 
class Game:
    def isCollision(self,x1,y1,x2,y2,bsize):
        if x1 >= x2 and x1 <= x2 + bsize:
            if y1 >= y2 and y1 <= y2 + bsize:
                return True
        return False
 
class App:
 
    windowWidth = 800
    windowHeight = 600
    player = 0
    apple = 0
 
    def __init__(self):
        self._running = True
        self._display_surf = None
        self._image_surf = None
        self._apple_surf = None
        self.game = Game()
        self.player = Player(5) 
        self.apple = Apple(8,5)
        self.computer = Computer(5)
 
    def on_init(self):
        pygame.init()
        self._display_surf = pygame.display.set_mode((self.windowWidth,self.windowHeight), pygame.HWSURFACE)
 
        pygame.display.set_caption('Pygame pythonspot.com example')
        self._running = True
        self._image_surf = pygame.image.load("pygame.png").convert()
        self._apple_surf = pygame.image.load("apple.png").convert()
 
    def on_event(self, event):
        if event.type == QUIT:
            self._running = False
 
    def on_loop(self):
        self.computer.target(self.apple.x, self.apple.y)
        self.player.update()
        self.computer.update()
 
        # does snake eat apple?
        for i in range(0,self.player.length):
            if self.game.isCollision(self.apple.x,self.apple.y,self.player.x[i], self.player.y[i],44):
                self.apple.x = randint(2,9) * 44
                self.apple.y = randint(2,9) * 44
                self.player.length = self.player.length + 1
 
        # does computer eat apple?
        for i in range(0,self.player.length):
            if self.game.isCollision(self.apple.x,self.apple.y,self.computer.x[i], self.computer.y[i],44):
                self.apple.x = randint(2,9) * 44
                self.apple.y = randint(2,9) * 44
                #self.computer.length = self.computer.length + 1
 
 
        # does snake collide with itself?
        for i in range(2,self.player.length):
            if self.game.isCollision(self.player.x[0],self.player.y[0],self.player.x[i], self.player.y[i],40):
                print "You lose! Collision: "
                print "x[0] (" + str(self.player.x[0]) + "," + str(self.player.y[0]) + ")"  
                print "x[" + str(i) + "] (" + str(self.player.x[i]) + "," + str(self.player.y[i]) + ")"  
                exit(0)
 
        pass
 
    def on_render(self):
        self._display_surf.fill((0,0,0))
        self.player.draw(self._display_surf, self._image_surf)
        self.apple.draw(self._display_surf, self._apple_surf)
        self.computer.draw(self._display_surf, self._image_surf)
        pygame.display.flip()
 
    def on_cleanup(self):
        pygame.quit()
 
    def on_execute(self):
        if self.on_init() == False:
            self._running = False
 
        while( self._running ):
            pygame.event.pump()
            keys = pygame.key.get_pressed() 
 
            if (keys[K_RIGHT]):
                self.player.moveRight()
 
            if (keys[K_LEFT]):
                self.player.moveLeft()
 
            if (keys[K_UP]):
                self.player.moveUp()
 
            if (keys[K_DOWN]):
                self.player.moveDown()
 
            if (keys[K_ESCAPE]):
                self._running = False
 
            self.on_loop()
            self.on_render()
 
            time.sleep (50.0 / 1000.0);
        self.on_cleanup()
 
if __name__ == "__main__" :
    theApp = App()
    theApp.on_execute()
python snake
python snake

Conclusion
You learned how to create a basic computer player using an very simple AI algorithm.

Next:  Learn basic sidescroller logic