W2514 Emergence & Lindenmayer Systems (Part 4)

Within these castle walls be forged Mavens of Computer Science ...

— Merlin, The Coder

Emergence & Lindenmayer Systems (Part 4)

Fractal Tree

Prerequisites

• Emergence & Lindenmayer Systems (Part 3)

Research

• Read Stacks
• Review those Lindenmayer Systems that require use of a stack (pop/push). One example is a "Fractal Tree".

Experiment

Getting Started

Continue with the previous project.

Enter into the Sources directory of the new project.

cd ~/projects/IgisShell-LSystems/Sources/IgisShell/

First Steps

Stack

Turtle objects are able to remember their current state and restore that state at a later point. The state is stored on a stack and is therefore in LIFO order. A turtle's state includes:

• location
• angle
• pen color
• pen width

Consider a Fractal Tree with the following translation mechanisms:

• 0: draw a line segment (ending in a leaf)
• 1: draw a line segment
• [: push position and angle, turn left 45 degrees
• ]: pop position and angle, turn right 45 degrees

When encountering a push or pop operation we can use the turtle's functionality as follows:

           case "[":
                turtle.push()
                turtle.left(degrees:45)
           case "]":
                turtle.pop()
                turtle.right(degrees:45)

Exercises

1. Add a Fractal Tree as one of the Lindenmayer Systems in your cycle
2. Add a Fractal Plant as one of the Lindenmayer Systems in your cycle

Key Concepts

• A Stack is an abstract data-type which is a collection of elements with two principal operations:
  • Push adds the specified element to the collection
  • Pop removes the most recently added element
• LIFO means Last in, first out