Held: Friday, 30 October 2015

Back to Outline 32 - Naming Local Procedures. On to Outline 34 - Iteration.

Summary

We explore another imperative model of images, turtle graphics. In this model, we give drawing expressions to simulated robotic turtles.

Related Pages

• Reading: Turtle Graphics
• Lab: Turtle Graphics
• EBoard 33 (Source 33)

Overview

• Modeling images through process: Turtle graphics.
• Some historical notes.
• Turtle graphics in MediaScheme.

Administrivia

• Continue partners.
• QQL day (questions, quiz, lab).
• Notes on lab 30 are still available.
• Notes on exam 2 to be distributed over the weekend.
• Happy Birthday EG!
• Friday PSA.

Upcoming Work

• Reading for Monday: Iteration
• HW 6 due next Tuesday.
  • May be a few bugs in part A.
• Looking ahead: Exam 3, Project Proposal, Project, Exam 4, Done.
• Today's Lab writeup (due before class Tuesday)
  • Email to grader-151-01@cs.grinnell.edu
  • Subject: CSC 151 Lab Writeup Class 33 (Your Names)
  • Exercises:

Extra Credit Opportunities

• If possible, send me these in advance.

Academic

• Any visit to the current show in the Faulconer gallery.
• R.L. Stephens II events Friday.
• Expressing Yourself Inside and Outside the Classroom: A Faculty Panel. Friday, noon, JRC 209. (With Prof. Katya, SamR, Prof. Praitis, Prof. Willig Onwuachi, and Prof. Byrd)
• CS Table Tuesday: Why people support and bully online.
• Sexual Misconduct at Grinnell College: Results from the 2013 and 2015 Sexual Conduct Surveys. 1-3 pm, November 8, JRC 101.

Peer Support

• Thursday at 7pm, Womens BBall (scrimmage vs MCC)
• Spark Tank, Wednesday, 7pm in Roberts Theatre in Bucksbaum.
• Pals of PALS, pals@grinnell.edu, normally Saturday at 7:45 am (breakfast included), Sunday at 4:45, and Mondays at 4:45. Requires sign up in advance.
• Socrates Cafe', Saturdays, Younker, 2pm.
• Pun Club, Saturdays, 4pm, Way over Younker.

Upcoming Peer Support

• November 14, Orchestra Concert, Sebring Lewis, 7:30 p.m.
• Women's Basketball Opening Game, 1pm, Nov. 15, vs. Silver Lake.
• One-act Festival Dec. 5 & 6.

Other Good Stuff to Do

• Women's Soccer Saturday
• Men's Soccer Saturday
• Halloween event Saturday

Modeling the Drawing Process: Turtle Graphics

• We've now seen three (more?) models of making images:
  • We can use drawings-as-values-style graphics to build composite images.
  • We can use GIMP-style graphics to select and then do something with the selection.
  • We can manipulate individual pixels
  • We can transform images
• These models permit us to create a variety of interesting drawings.
• However, they do not model how we normally draw, which involves taking pen (or brush) to paper (or canvas).
• The turtle graphics approach to describing images provides a simple model for how we might describe drawings.
• At any point, the person following the instructions has a pen in hand. You need to give the person information on the direction in which to move the pen and the amount to move it. (That's right, no curves here; just lots and lots of straight lines.)
• We separate the two basic operations: You can tell the person drawing to move forward or to turn in a particular direction.
• "It's so simple, even a turtle can do it."
• What if you don't want continuous lines? You can tell the turtle to lift or drop the pen.
• Turtle graphics has been used to control robots that draw.
• Note that turtle graphics, much like GIMP graphics, is an "imperative" model: You give a series of commands to the thing doing the drawing.

Some Historical Notes

Disclaimer: Although I knew much of this information, I did crib some ideas from Wikipedia and the Web for these notes.

• Turtle graphics were invented by Seymour Papert (at MIT) in part of his development of the LOGO programming language. (1960's and beyond)
• LOGO was designed as a computer language intended to help children think better (or at least more algorithmically).
• The original implementation of LOGO did, in fact, have a kind of robot (commonly referred to as a turtle robot) hooked up to a computer. Hence, it made sense for the language to have some basic operations for the robot.
• As computers became more commonplace, it made sense to simulate the turtle on the screen (since not everyone who had a computer would have a turtle robot).
• And it makes sense to show the turtle's path.
• After awhile, drawing on the screen became as interesting as (or more interesting than?) controlling the physical robot.
• The turtle graphics model has persisted, in various forms, over the years.
• Turtle graphics and LOGO are often used in constructionist approaches to teaching. The goal is that students explore freely, starting with a few basic tools and strategies, they come up with their own problems and develop solutions to those problems.

Turtle Graphics in MediaScheme

• Create a new turtle that draws on a particular image with (turtle-new image).
• Move it forward with (turtle-forward! turtle amt)
• Turn it with (turtle-turn! turtle angle)
• Lift the pen with (turtle-up! turtle)
• Put the pen on paper with (turtle-down! turtle)
• Additional operations for people who can't keep track of position and orientation
  • (turtle-teleport! turtle col row)
  • (turtle-face! turtle angle)
  • (turtle-show! turtle)
• You can also set the turtle's brush and color.

Lab

• Make and predict some fun pictures.