Activities/Turtle Art-0.86

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Where to get Turtle Art

Note: The first time you run Turtle Art, it takes about 30 seconds to load. You'll see a mostly blank screen after the initial flashing of the icon. Subsequently, the loading time is ~5 seconds (on an OLPC-XO-1 laptop).

Background

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

Turtle Art is intended to be a stepping stone to the Logo programming language, but there are many restrictions compared to Logo. (Only numeric global variables and stack items are available, no lists or other data-structures. The conditionals and some of the functions only take constants or variables, not expressions. Limited screen real-estate makes building large programs unfeasible.) However, you can export your Turtle Art creations to Berkeley Logo. Turtle Art also has a (limited) facility for sensor input, so, for example, you can move the Turtle based upon sound volume or pitch.

Turtle Art was written by Brian Silverman and is maintained by Walter Bender. Arjun Sarwal added the sensor features. Luis Michelena contributed to the "named" action and box blocks..

Learning with Turtle Art

Play with Turtle Art to draw colorful art patterns using a turtle that accepts instructions for movement.

With visual programming blocks, you can snap together programs by compiling (combining) them in ways to create anything you can imagine.

What am I learning?

You are learning how to build a set of instructions for a pretend turtle to follow. With repeating instructions and conditional following of the instructions, your pretend turtle can draw shapes and lines over and over again with interesting results.

Why is this important?

You learn to predict what each instruction will cause the turtle to create with line art. It helps you detect patterns, understand the repetition of instructions, and understand following instructions only when a certain condition is met, which is important in computer programming, mathematics, and science.

Getting Started

Start by clicking on (or dragging) blocks from the Turtle palette. Use multiple blocks to create drawings; as the turtle moves under your control, colorful lines are drawn.

You add blocks to your program by clicking on or dragging them from the palette to the main area. You can delete a block by dragging it back onto the palette. Click anywhere on a "stack" of blocks to start executing that stack or by clicking in the Rabbit (fast) or Turtle (slow) buttons on the Project Toolbar.

Project Toolbar

From left to right: show/hide palette; show/hide blocks; run project fast; run project slow; stop project; erase canvas; load sample project; save as Logo

Keyboard short cuts for the above: palette; blocks; run; walk; stop; erase

Notes: The run buttons are tied to the Start Block. If no Start Block is used, then all blocks are run when either run button is clicked. The "rabbit" button runs the blocks at maximum speed. The "turtle" button pauses and displays the turtle between each step.

Palettes

There are six palettes of program elements available for program construction: Turtle movements; Pen attributes; Numeric operators; Sensor inputs; Logical operators; and Logical blocks

The Turtle Palette (green)

examples (1)

descriptions (1)

	Clean	clear the screen and reset the turtle to center, pointed up (pen down, bright red)
	Forward (number)	move turtle forward
	Back (number)	move turtle backward
	Left (angle in degrees)	turn turtle counterclockwise
	Right (angle in degrees)	turn turtle clockwise
	Arc (angle in degrees,radius)	move turtle along an arc
	Setyx (xcor, ycor)	move turtle to position (xcor, ycor) [(0, 0) is in the center of the screen.]
	Seth (heading)	set the heading of the turtle [0 is towards the top of the screen.]
	Text (size)	draw text next to the turtle
	Image	draw image (click on the Journal icon to search for an image from the Journal
	X coordinate	holds current x-coordinate value of the turtle (can be used in place of a number block)
	Y coordinate	holds current y-coordinate value of the turtle (can be used in place of a number block)
	Heading	holds current heading value of the turtle (can be used in place of a number block)

Turtle state values (can plug into a parameter):

X, Y – Zeros for each are at center screen. Negative values are left and down; positive values are right and up.
Heading – Zero is pointed up. Heading is in degrees clockwise.
Angles are degrees from 0 to 360 (for larger values and smaller values all multiples of 360 are subtracted or added to get the value into the range 0..360).

Examples: 90 means a right angle (90 degrees), clockwise; –30 means a 30-degree angle, counterclockwise

The Pen Palette (cyan)

examples (2)

descriptions (2)

	Pen Up	turtle will not draw when moved
	Pen Down	turtle will draw when moved
	Set Pen Size (number)	set size of the line drawn by the turtle
	Set Pen Color (number)	set color of the line drawn by the turtle
	Set Pen Shade (number)	set shade of the line drawn by the turtle
	Set Text Color (number)	set color of text drawn by the turtle
	Fill Screen(color,shade)	fills the background with (color, shade)
	Pen size
	Pen color
	Pen 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. Color specifies a hue and shade specifies an admixture of white or black to the color.

The Numbers Palette (purple)

examples (3)

descriptions (3)

	number	used as numeric input in mathematic operators
	addition	adds two numeric inputs
	subtraction	subtracts bottom numeric input from top numeric input
	product	multiplies two numeric inputs
	division	divides top numeric input (numerator) by bottom numeric input (denominator)
	mod	modular (remainder) operator
	numeric extensions	identity operators used for extending blocks (See example above)
	square root	calculate square root
	random	returns random number between minimum (left) and maximum (right) values
	equal?	logical = operator (plugs into an If blocks on the Flow Palette)
	greater?	logical > operator (plugs into an If blocks on the Flow Palette)
	less?	logical < operator (plugs into an If blocks on the Flow Palette)
	and	logical ⋀ (and) operator (links conditional)
	or	logical ⋁ (or) operator (links conditional)
	not	logical ￢ (not) operator (links conditional)
	print	Prints value in status block at bottom of the canvas (See example above)

The Sensors Palette (red)

(OLPC XO-1 only)

examples (4)

descriptions (4)

	volume	microphone input volume
	pitch	microphone input pitch
	voltage	(OLPC XO-1 only)
	resistance	(OLPC XO-1 only)

More details on how to use the sensors can be found on the Measure Activity page.

The Flow Palette (orange)

examples (5)

descriptions (5)

	Wait(number)	wait specified number of seconds
	Forever[stack]	(no continuation)
	Repeat(number)[stack]	loop specified number of times
	If(condition)[then]	uses boolean operators from Numbers palette
	-If(condition)[then][else]	uses boolean operators from Numbers palette
	Stop Stack	No continuation of current action
	horizontal spacer	jog stack right
	vertical spacer	jog stack down

The My Blocks Palette (yellow)

examples (6)

descriptions (6)

	start	connects action to toolbar run buttons
	action 1 "hat"	top of action 1 stack
	action 1	invoke action 1 stack
	action 2 "hat"	top of action 2 stack
	action 2	invoke action 2 stack
	nameable action "hat"	top of named action stack
	nameable action	invoke named action stack
	store in box 1	store numeric value in variable 1
	box 1	variable 1 (numeric value)
	store in box 2	store numeric value in variable 2
	box 2	variable 2 (numeric value)
	store in nameable box	store numeric value in named variable
	nameable box	named variable (numeric value)
	push	push value onto FILO (first-in last-out) heap
	pop	pop value off FILO
	show heap	show FILO in status block at bottom of canvas
	empty heap	empty FILO

Looking under the hood

Turtle Art projects are stored as two files: (1) a .ta file contains a json-encoded serialization of the project; and (2) a .png file of the canvas.

The json encoding of a repeat 4 forward 100 right 90 project:

[[0,"repeat",331,158,[null,1,2,null]],[1,["number","4"],417,167,[0,null]],[2,"forward",426,207,[0,3,4]],[3,["number","100"],500,216,[2,null]],[4,"right",426,246,[2,5,null]],[5,["number","90"],500,255,[4,null]],[-1,"turtle",0,0,0,0,50,5]]