Lesson 6

Turtle Graphics

Similar to the Pen Tools extension in Scratch.

Useful for:

drawing polylines
making patterns/art

Turtle Graphics in pycat

In pycat, the Turtle class is a special kind of Sprite that draws line segments whenever it moves_forward.

Turtle Creation

from pycat.extensions.turtle import Turtle

t = w.create_sprite(Turtle)

Turtle Methods

turtle.turn_left(degrees: float)
turtle.turn_right(degrees: float)
turtle.pen_up()
turtle.pen_down()

Turtle Properties

turtle.pen_color
turtle.pen_width

Exercise

Write a program that creates a Turtle and draws a simple shape.

find an image to use for your turtle (make sure it faces right)
experiment with the turtle methods and properties listed above

For Loops

for i in range(4):
    print(i)

What will this draw?

for _ in range(4):
    t.move_forward(10)
    t.rotation += 90

for _ in range(4):
    t.pen_down()
    t.move_forward(5)
    t.pen_up()
    t.move_forward(5)

Exercise

Draw some shapes using for loops. Possible shapes include:

Square
Regular Polygon
Circle
Star
Spiral

After you finish a few different shapes, try to make them using dotted lines.

Functions

Let’s make a function to draw a square together:

def draw_square():
    pass

Exercise

Create functions for the shapes you made in the previous exercise

Function Arguments

Part 1

How can we make our functions more generic/useful?

def draw_square(size: float):
    pass

Exercise

Rewrite your functions to be more generic

Part 2

What if we have multiple turtles in our file?

Exercise

Rewrite your functions to be generic

Extensions

Regular Polygon

def draw_regular_polygon(sides: int, side_length: float):
    pass

def draw_regular_polygon(sides: int, side_length: float, is_dashed: bool):
    pass

User-controlled Turtle

class InteractiveTurtle(Turtle):

    def on_update(dt):
        if w.get_key(KeyCode.W):
           pass

Homework

Homework 4