Tutorial #4

Collision With Snack

Now that we’ve created the snack we need to draw it and see if the head of our snake collides with it.

Our redrawWindow() function should now look like this:

def redrawWindow(surface):
    global rows, width, s, snack # ADD snack to this line
    surface.fill((0,0,0))
    s.draw(surface)
    snack.draw(surface) # NEW
    drawGrid(width,rows, surface)
    pygame.display.update()

To check for collision we will add the following lines into our game loop within the main() function.

if s.body[0] == snake.pos:  # Checks if the head collides with the snack
    s.addCube()  # Adds a new cube to the snake
    snack = cube(randomSnack(rows, s), color=(0,255,0))  # creates a new snack object

Snake Class – addCube() Method

The last step to adding a cube is to add it to the end of our snake object. We will do this from the addCube() method.

class snake():
    ...    
    def addCube(self):
        tail = self.body[-1]
        dx, dy = tail.dirnx, tail.dirny
        
        # We need to know which side of the snake to add the cube to.
        # So we check what direction we are currently moving in to determine if we
        # need to add the cube to the left, right, above or below.
        if dx == 1 and dy == 0:
            self.body.append(cube((tail.pos[0]-1,tail.pos[1])))
        elif dx == -1 and dy == 0:
            self.body.append(cube((tail.pos[0]+1,tail.pos[1])))
        elif dx == 0 and dy == 1:
            self.body.append(cube((tail.pos[0],tail.pos[1]-1)))
        elif dx == 0 and dy == -1:
            self.body.append(cube((tail.pos[0],tail.pos[1]+1)))
        
        # We then set the cubes direction to the direction of the snake.
        self.body[-1].dirnx = dx
        self.body[-1].dirny = dy

Ending the Game

We lose the game when our snake object collides with itself. To check this we add the following line to our main() function inside the game loop.

for x in range(len(s.body)):
    if s.body[x].pos in list(map(lambda z:z.pos,s.body[x+1:])): # This will check if any of the positions in our body list overlap
        print('Score: ', len(s.body))
        message_box('You Lost!', 'Play again...')
        s.reset((10,10))
        break

Snake Class – reset() Method

Now we will code the reset() method from within the snake class. All this will do is reset the snake so we can play again afterwards.

class snake():
    ...
    def reset(self, pos):
        self.head = cube(pos)
        self.body = []
        self.body.append(self.head)
        self.turns = {}
        self.dirnx = 0
        self.dirny = 1

Displaying a Message Box

When the user losses we want to display a message box telling them that they lost.

We are going to do this using tkinter and inside of our message_box() function.

import tkinter as tk
from tkinter import messagebox

def message_box(subject, content):
    root = tk.Tk()
    root.attributes("-topmost", True)
    root.withdraw()
    messagebox.showinfo(subject, content)
    try:
        root.destroy()
    except:
        pass

And now our game is finished!

Full Code

#Snake Tutorial Python

import math
import random
import pygame
import tkinter as tk
from tkinter import messagebox

class cube(object):
    rows = 20
    w = 500
    def __init__(self,start,dirnx=1,dirny=0,color=(255,0,0)):
        self.pos = start
        self.dirnx = 1
        self.dirny = 0
        self.color = color

        
    def move(self, dirnx, dirny):
        self.dirnx = dirnx
        self.dirny = dirny
        self.pos = (self.pos[0] + self.dirnx, self.pos[1] + self.dirny)

    def draw(self, surface, eyes=False):
        dis = self.w // self.rows
        i = self.pos[0]
        j = self.pos[1]

        pygame.draw.rect(surface, self.color, (i*dis+1,j*dis+1, dis-2, dis-2))
        if eyes:
            centre = dis//2
            radius = 3
            circleMiddle = (i*dis+centre-radius,j*dis+8)
            circleMiddle2 = (i*dis + dis -radius*2, j*dis+8)
            pygame.draw.circle(surface, (0,0,0), circleMiddle, radius)
            pygame.draw.circle(surface, (0,0,0), circleMiddle2, radius)
        



class snake(object):
    body = []
    turns = {}
    def __init__(self, color, pos):
        self.color = color
        self.head = cube(pos)
        self.body.append(self.head)
        self.dirnx = 0
        self.dirny = 1

    def move(self):
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()

            keys = pygame.key.get_pressed()

            for key in keys:
                if keys[pygame.K_LEFT]:
                    self.dirnx = -1
                    self.dirny = 0
                    self.turns[self.head.pos[:]] = [self.dirnx, self.dirny]

                elif keys[pygame.K_RIGHT]:
                    self.dirnx = 1
                    self.dirny = 0
                    self.turns[self.head.pos[:]] = [self.dirnx, self.dirny]

                elif keys[pygame.K_UP]:
                    self.dirnx = 0
                    self.dirny = -1
                    self.turns[self.head.pos[:]] = [self.dirnx, self.dirny]

                elif keys[pygame.K_DOWN]:
                    self.dirnx = 0
                    self.dirny = 1
                    self.turns[self.head.pos[:]] = [self.dirnx, self.dirny]

        for i, c in enumerate(self.body):
            p = c.pos[:]
            if p in self.turns:
                turn = self.turns[p]
                c.move(turn[0],turn[1])
                if i == len(self.body)-1:
                    self.turns.pop(p)
            else:
                if c.dirnx == -1 and c.pos[0] <= 0: c.pos = (c.rows-1, c.pos[1])
                elif c.dirnx == 1 and c.pos[0] >= c.rows-1: c.pos = (0,c.pos[1])
                elif c.dirny == 1 and c.pos[1] >= c.rows-1: c.pos = (c.pos[0], 0)
                elif c.dirny == -1 and c.pos[1] <= 0: c.pos = (c.pos[0],c.rows-1)
                else: c.move(c.dirnx,c.dirny)
        

    def reset(self, pos):
        self.head = cube(pos)
        self.body = []
        self.body.append(self.head)
        self.turns = {}
        self.dirnx = 0
        self.dirny = 1


    def addCube(self):
        tail = self.body[-1]
        dx, dy = tail.dirnx, tail.dirny

        if dx == 1 and dy == 0:
            self.body.append(cube((tail.pos[0]-1,tail.pos[1])))
        elif dx == -1 and dy == 0:
            self.body.append(cube((tail.pos[0]+1,tail.pos[1])))
        elif dx == 0 and dy == 1:
            self.body.append(cube((tail.pos[0],tail.pos[1]-1)))
        elif dx == 0 and dy == -1:
            self.body.append(cube((tail.pos[0],tail.pos[1]+1)))

        self.body[-1].dirnx = dx
        self.body[-1].dirny = dy
        

    def draw(self, surface):
        for i, c in enumerate(self.body):
            if i ==0:
                c.draw(surface, True)
            else:
                c.draw(surface)


def drawGrid(w, rows, surface):
    sizeBtwn = w // rows

    x = 0
    y = 0
    for l in range(rows):
        x = x + sizeBtwn
        y = y + sizeBtwn

        pygame.draw.line(surface, (255,255,255), (x,0),(x,w))
        pygame.draw.line(surface, (255,255,255), (0,y),(w,y))
        

def redrawWindow(surface):
    global rows, width, s, snack
    surface.fill((0,0,0))
    s.draw(surface)
    snack.draw(surface)
    drawGrid(width,rows, surface)
    pygame.display.update()


def randomSnack(rows, item):

    positions = item.body

    while True:
        x = random.randrange(rows)
        y = random.randrange(rows)
        if len(list(filter(lambda z:z.pos == (x,y), positions))) > 0:
            continue
        else:
            break
        
    return (x,y)


def message_box(subject, content):
    root = tk.Tk()
    root.attributes("-topmost", True)
    root.withdraw()
    messagebox.showinfo(subject, content)
    try:
        root.destroy()
    except:
        pass


def main():
    global width, rows, s, snack
    width = 500
    rows = 20
    win = pygame.display.set_mode((width, width))
    s = snake((255,0,0), (10,10))
    snack = cube(randomSnack(rows, s), color=(0,255,0))
    flag = True

    clock = pygame.time.Clock()
    
    while flag:
        pygame.time.delay(50)
        clock.tick(10)
        s.move()
        if s.body[0].pos == snack.pos:
            s.addCube()
            snack = cube(randomSnack(rows, s), color=(0,255,0))

        for x in range(len(s.body)):
            if s.body[x].pos in list(map(lambda z:z.pos,s.body[x+1:])):
                print('Score: ', len(s.body))
                message_box('You Lost!', 'Play again...')
                s.reset((10,10))
                break

            
        redrawWindow(win)

main()

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