Class 33: Turtle Graphics
Held: Monday, 3 April 2017
We explore another imperative model of images, *turtle graphics. In this model, we give drawing instructions to simulated robotic turtles.*
Preliminaries
Overview
- {“Modeling images through process”=>”Turtle graphics”}
- Some historical notes
- Turtle graphics in MediaScheme
Related Pages
-
Reading: Turtle Graphics
-
Lab: Turtle Graphics
Updates
News / Etc.
- New partners!
- Welcome back from break. I hope that you found it enjoyable and relaxing.
- I’m pausing on returning exams for a few days. Sorry, but there are good reasons.
- Congrats to baseball for sweeping Blueboys!
Rotating reminders
- Get news! Feel free to ask me to sign you up for the department mailing list.
Upcoming Work
- Lab writeup: TBD.
- Homework 7 to be distributed Wednesday. Our last homework! (We do have two exams and a project left.)
- Reading for Tuesday: Iteration
Extra credit (Academic/Artistic)
- Today at 4:15 p.m., JRC 101: “Sad! Or Stronger Than Ever? American Journalism in the Age of Fake News, Social Media, and Donald Trump.”
- Tomorrow at 4:15 p.m. JRC 101: The 1st Mando lecture. “Reflections By Pulitzer-Prize-winning writer Dale Maharidge & photographer Michael Williamson.”
- BAX Opening Reception (plus Robert Hodierne photographs) Friday 4:30-5:30
Extra credit (Peer)
- Baseball games Saturday at 1pm and 3:30 pm vs. Monmouth (if it ever stops raining)
Extra credit (Misc)
None right now.
Good things to do
- Track and Field Saturday at Cornell at 11 am. (Do we have any Trackers or Fielders?)
- Women’s Tennis Saturday at 10:00 am
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.