Turtle Art


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Turtle Art
Image:Turtleart.png This activity was bundled
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Brian Silverman

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Turtle Art is an activity with a Logo-inspired graphical "turtle" that draws colorful art based on Scratch-like snap-together visual programming elements.

There are many restrictions compared to LOGO. The two allowed user-defined procedures can't have parameters. Only two numeric global variables are available, no lists or other data-structures. You can't make user defined functions which return a value. The conditionals and some of the functions only take constants or variables, not expressions. Limited screen real-estate makes building large programs unfeasible.

Help write the Turtle Art student guide!



There are five palettes of program elements available for program construction. You add blocks to your program by dragging them from the palette to the main area. You can delete a block by dragging it back onto the palette. Click anywhere on an existing "stack" of blocks to start executing that stack.

Turtle (green)

  • Clean - clear the screen and reset the turtle to center, pointed up (pen down, bright red)
  • Forward(n)
  • Back(n)
  • Left(angle)
  • Right(angle)
  • Arc(angle,radius)
  • SetYX(x,y)
  • SetH(heading)
  • Turtle state values (can plug into a parameter)
    • X, Y, heading (Zeros for each are center screen, pointed up. Heading is degrees clockwise.)
    • angles are degrees from 0 to 360 (for larger values and smaller values all multiples of 360 are substracted or added to get the value into the range 0..360).
    • Example: 90 means a right angle clockwise, -30 means a 30 degree angle counterclockwise

Pen (cyan)

  • Pen Up
  • Pen Down
  • Set Pen Size(n)
  • Set Color(n)
  • Set Shade(n)
  • Fill Screen(color,shade)
  • Pen state values (can plug into a parameter)
    • Pen size, color, shade
    • Colors and shades are represented by a number from 0 through 99. Using a number outside of this range is allowed, and will cause the value to be "wrapped around" (via a modulo, or "clock arithmetic" operation) to the 0 - 99 range.

This image shows the correspondence between the color's representative number and the actual color itself. NOTE: Some of these colors will appear differently on the XO screen than they do on a standard computer screen. This image is taken from a screenshot on a Macintosh Mini using Firefox to view this webpage.


Here is a photograph of the Browser Activity on the XO displaying the original website for the preceding image. It should be taken with a large grain of salt, since it is a photo of a laptop screen, and is thus a pretty poor way to reliably show colors. To see the colors available in Turtle Art, the original website should be viewed on an actual XO.


Numbers (violet)

  • Values (can plug into a parameter)
    • Number (constant)
    • Infix operators(left,right)
      • +, -, *, /, mod
    • Random(min, max) (constants or boxes only)
  • Conditions (oval, plugs into an If block)
    • <, >, = (takes two constants or boxes)
    • and, or, not (takes other conditions)
  • Print(n) - Debugging output. When in full screen mode (Alt-Enter), show a numeric value at the bottom of the screen.

Flow (orange)

  • Wait(n)
  • Forever[stack] (no continuation)
  • Repeat(n)[stack]
  • If(condition)[then]
  • If(condition)[then][else]
  • Stop (no continuation)
  • Connectors:
    • jog right
    • jog down

My blocks (yellow)

  • Stack1,2 - a rhombus which tops a stack, equivalent to a procedure definition (but without parameters).
  • "Stack1,2" - blocks for invoking a stack (no parameters)
  • Store in "box" 1,2(n) - blocks for setting a variable
  • "Box1,2" (plugs into a parameter)
    • A glaring limitation: you cannot rename these objects. Thus, you are limited to two procedures and two global variables! Madness! --IanOsgood 13:59, 30 December 2007 (EST)

Program control icons

There are also some icons at the bottom right for user control:

  • Show/Hide the current program
  • Eraser - clear the screen and reset the turtle (same as the Clean block)
  • Stop (for infinite loops)

Project tab

The Project tab at the top left gives access to sample programs shipped with the activity.

See also


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