Branch Assignment

Reference

Lindenmayer system

Array

push

pop

OpenGL

glPushMatrix

glPopMatrix

Code to Investigate

LogoTurtle

The turtle you will use in this assignment is inspired by the Turtle Graphics in the [Logo Programming Language] created by Wally Feurzeig, Seymour Papert, and Cynthia Solomon. The turtle was a robot which would draw with a pen on paper place on the floor. We will less excitingly draw on the screen with OpenGL.

A primer on how to use a turtle in its native habitat.

The provided class LogoTurtle below provides methods to get and set its pen color and width, pick the pen up and put it down, move forward, and turn right in degrees.

Note: attr_accessor :pen_color, :pen_width provides pen_color, pen_color=, pen_width, and pen_width= methods.

class LogoTurtle
  attr_accessor :pen_color, :pen_width
  def initialize
    super
    @is_pen_down = true
    @pen_width = 0.005
    @pen_color = Color::WHITE
  end

  def pen_up
    @is_pen_down = true
  end

  def pen_down
    @is_pen_down = false
  end


  def forward(amount)
    y = amount
    x = @pen_width
    if @is_pen_down
      glColor3f(@pen_color.red, @pen_color.green, @pen_color.blue)
      glBegin(GL_QUADS)
      glVertex2d(-x, 0.0)
      glVertex2d(-x, y)
      glVertex2d(x, y)
      glVertex2d(x, 0.0)
      glEnd()
    end
    glTranslatef(0,y,0)
  end

  def right(degrees)
    glRotatef(degrees, 0, 0, 1)
  end
end

Flower Client

In this example client, a square is drawn by repeatedly moving forward and turning right 90 degrees. The flower is drawn by repeatedly drawing slightly turned from each other squares.

class Flower
  def initialize
    super
    @turtle = LogoTurtle.new
  end

  def render
    flower
  end

  private

  def square
    4.times do
      @turtle.forward 0.5
      @turtle.right 90
    end
  end

  def flower
    36.times do
      @turtle.right 10
      square
    end
  end
end

file to run:

src/main/ruby/render/logo/flower.rb

Code to Implement

TeleportingTurtle

file:	src/main/ruby/branch/teleporting_turtle.rb
class:	TeleportingTurtle
superclass:	Turtle
methods:	preserve_yield_restore

This utility method will simply preserve the current state, yield to the block passed by the client, and then restore the preserved state.

Note: the private preserve_state and restore_state methods have been provided to you.

Branch

file:	src/main/ruby/branch/branch.rb
class:	Branch
superclass:	Object
methods:	push_do_pop render

The goal of this assignment is to render a branch that looks something akin to the progression of max_depth branches below.

Note: the initialize method constructs a new instance of TeleportingTurtle as well as hangs onto the parameter values in instance variables.

max_depth: 0	max_depth: 1	max_depth: 2	max_depth: 3	max_depth: 4	max_depth: 5

branch(length, line_width_in_pixels, depth_remaining)

Pass a block to #push_do_pop to handle the preservation and restoration of the necessary OpenGL and LogoTurtle state.

Note: to produce the reference images the code below was used:

      next_length = length * 0.5
      next_line_width_in_pixels = line_width_in_pixels * 0.8

Note: the child branches in the reference images are located at one third and at two thirds from the beginning to the end.

Note: the child branches in the reference images are rotated 30.0 degrees and -30.0 degrees from their parent branch.

Note: in the recursive case the child branches were drawn before the line at the current depth to allow the green to be beneath the brown.

Do NOT worry if your images are not exact matches of the reference images.

Run

file to run:

src/main/ruby/render/branch/branch.rb

Visual Comparison

file to run:

src/main/ruby/drawings_snapshots/part_a_snapshots_web_page_generator.rb