What's the turtle chomping?

OK, so now you have your turtle which you can move around the screen. If it bumps into any of the borders, your turtle will bounce off at 180°.

Now we need an objective for the game, something for your turtle to do and to score points for doing. For this game, you are going to have your turtle chase and chomp space cabbages (because we are making a green, circle object for your turtle to chase). You could choose a different colour and shape such as space cheese (e.g. yellow triangle).

Step 1.

Create the goal/objective, type the following under a # Create food section after player.speed(0)

# Create food
food = turtle.Turtle()
food.color("lightgreen")
food.shape("circle")
food.penup()
food.speed(0)

Step 2.

Save the game as kbgame4.py and then run the module.

Step 3.

Now we are going to set the cabbage in a position by typing the following after food.speed(0):

food.setposition(-100, 100) 

Step 4.

Save and run module kbgame4.

Step 5.

Next, we need to add collision detection, as this will allow us to determine when your turtle collides with (chomps) the space cabbage. We do this by using a bit of math to work out where the turtle and cabbage is and if they are touching or the distance between them is small. For the math nerds here, we will use the the Pythagorean theorem. To do that we need to import the math libraries at the top of our application after import turtle:

# Turtle Graphics Game – Space Turtle Chomp
import turtle
import math

Step 6.

Now, we will write the math formula. It takes the X-coordinate of the turtle, subtracts it from the X-coordinate of the cabbage, squares the result, does the same for the Y-coordinates, and finally calculates the square root. It’s OK not to completely understand (I’m not sure I do 😄) but you need to type the following at the end of your While Loop:

    # Collision checking
    d = math.sqrt(math.pow(player.xcor() - food.xcor(), 2) + math.pow(player.ycor() - food.ycor(),2))
    if d < 20:
        food.hideturtle()

Here we have that if the distance between the turtle and cabbage is less than 20 the cabbage (food) will hide.

Step 7.

Save and run the module, move your turtle to collide with the cabbage.

Now that works, we want to make the game more interesting as it will be a fairly boring game just to hide the cabbage. To make it more interesting, once the turtle collides with (chomps) the cabbage, we will move it to a random position.

For this to work we first need to import the random library at the top of your code just under the import math line:

import random

Step 8.

Now you set the random position within the x and y coordinates by replacing the line food.hideturtle to:

   
    if d < 20:
        food.setposition(random.randint(-290, 290), random.randint(-290, 290))

Step 9.

Save and run the module. We now have the basis of our game.

Step 10.

Now you can use the same random position option to randomise where the cabbage appears at the start of the game by replacing the food.setposition under the #create food section:

food.setposition(random.randint(-290, 290), random.randint(-290, 290))

Step 11.

Save and Run kbgame4.

Your code should now look like this:

#Turtle Graphics Game
import turtle
import math
import random

#Set up screen
turtle.setup(650,650)
wn = turtle.Screen()
wn.bgcolor("Navy")

#Draw border
mypen = turtle.Turtle()
mypen.color("white")
mypen.penup()
mypen.setposition(-300,-300)
mypen.pendown()
mypen.pensize(3)
for side in range(4):
    mypen.forward(600)
    mypen.left(90)
mypen.hideturtle()

#Create player turtle
player = turtle.Turtle()
player.color("darkorange")
player.shape("turtle")
player.penup()
player.speed(0)

#Create food
food = turtle.Turtle()
food.color("lightgreen")
food.shape("circle")
food.penup()
food.speed(0)
food.setposition(random.randint(-290, 290), random.randint(-290, 290))

#Set speed variable
speed = 1

#Define functions

def turn_left():
    player.left(30)

def turn_right():
    player.right(30)

def increase_speed():
    global speed
    speed += 1

#Set keyboard bindings
turtle.listen()
turtle.onkey(turn_left, "Left")
turtle.onkey(turn_right, "Right")
turtle.onkey(increase_speed, "Up")


while True:
    player.forward(speed)

    #Boundary Checking x coordinate
    if player.xcor() > 290 or player.xcor() < -290:
        player.right(180)
    #Boundary Checking y coordinate
    if player.ycor() > 290 or player.ycor() < -290:
        player.right(180)

    #Collision checking
    d = math.sqrt(math.pow(player.xcor()-food.xcor(),2) + math.pow(player.ycor()-food.ycor(),2))
    if d < 20:
        food.setposition(random.randint(-290, 290), random.randint(-290, 290))


delay = input("Press Enter to finish.")