Activities/Turtle Art-0.86


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Where to get Turtle Art

 

Version 32 .xo | Source | FLOSS Manual | laptop.org Turtle Art page | Student Guide | Portfolio (fork) | Turtle Art Gallery

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.

           


 
Calculating the hypotenuse and approximating the angle of a right triangle.
 
Stepping through the program is a nice way to visualize the process of approximation.
 
The final result of the approximation.


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

Turtle Art can export its projects to Logo (using the Save as Logo button on the Project Toolbar)

 
a Turtle Art project
 
the UCB Logo version

Note: The project is saved to the Journal as "logosession.lg". UCB Logo does not yet access the Journal directly, so it is necessary to copy the project out of the Journal using the "cppy-from-journal" command in the Terminal Activity and then accessing the project using the File menu within the UCB Logo Activity.

copy-from-journal -t logosession.lg

Internals

Some procedures for setting up the palette and the shade functionality:

to tasetpalette :i :r :g :b :myshade
make "s ((:myshade - 50) / 50)
ifelse lessp :s 0 [
make "s (1 + (:s *0.8))
make "r (:r * :s) 
make "g (:g * :s) 
make "b (:b * :s)
] [
make "s (:s * 0.9)
make "r (:r + ((100-:r) * :s)) 
make "g (:g + ((100-:g) * :s)) 
make "b (:b + ((100-:b) * :s))
]
setpalette :i (list :r :g :b)
end
to rgb :myi :mycolors :myshade
make "myr first :mycolors
make "mycolors butfirst :mycolors
make "myg first :mycolors
make "mycolors butfirst :mycolors
make "myb first :mycolors
make "mycolors butfirst :mycolors
tasetpalette :myi :myr :myg :myb :myshade
output :mycolors
end
to processcolor :mycolors :myshade
if emptyp :mycolors [stop]
make "i :i + 1
processcolor (rgb :i :mycolors :myshade) :myshade
end
to tasetshade :shade
make "myshade modulo :shade 200
if greaterp :myshade 99 [make "myshade (199-:myshade)]
make "i 7
make "mycolors :colors 
processcolor :mycolors :myshade
end
to tasetpencolor :c
make "color modulo round :c 100
setpencolor :color + 8
end
make "colors [
100 0 0 100 5 0 100 10 0 100 15 0 100 20 0 100 25 0 100 30 0 100 35 0 100 40 0 100 45 0 
100 50 0 100 55 0 100 60 0 100 65 0 100 70 0 100 75 0 100 80 0 100 85 0 100 90 0 100 95 0 
100 100 0 90 100 0 80 100 0 70 100 0 60 100 0 50 100 0 40 100 0 30 100 0 20 100 0 10 100 0 
0 100 0 0 100 5 0 100 10 0 100 15 0 100 20 0 100 25 0 100 30 0 100 35 0 100 40 0 100 45 
0 100 50 0 100 55 0 100 60 0 100 65 0 100 70 0 100 75 0 100 80 0 100 85 0 100 90 0 100 95 
0 100 100 0 95 100 0 90 100 0 85 100 0 80 100 0 75 100 0 70 100 0 65 100 0 60 100 0 55 100 
0 50 100 0 45 100 0 40 100 0 35 100 0 30 100 0 25 100 0 20 100 0 15 100 0 10 100 0 5 100 
0 0 100 5 0 100 10 0 100 15 0 100 20 0 100 25 0 100 30 0 100 35 0 100 40 0 100 45 0 100 
50 0 100 55 0 100 60 0 100 65 0 100 70 0 100 75 0 100 80 0 100 85 0 100 90 0 100 95 0 100 
100 0 100 100 0 90 100 0 80 100 0 70 100 0 60 100 0 50 100 0 40 100 0 30 100 0 20 100 0 10]
make "shade 50
tasetshade :shade
to tasetbackground :color :shade
tasetshade :shade
setbackground :color + 8
end

The project:

to ta
clearscreen tasetbackground 21 100 setpensize 25.0 make "box1 0.0 
repeat 300.0 [ tasetpencolor xcor / 6.0 tasetshade heading forward :box1 right 91.0 make "box1 :box1 + 1.0 ] 
end
ta

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]]