{"id":5969,"date":"2016-10-25T18:47:45","date_gmt":"2016-10-25T18:47:45","guid":{"rendered":"https:\/\/courses.ideate.cmu.edu\/15-104\/f2021\/?page_id=5969"},"modified":"2016-10-25T23:45:54","modified_gmt":"2016-10-25T23:45:54","slug":"turtle-graphics","status":"publish","type":"page","link":"https:\/\/courses.ideate.cmu.edu\/15-104\/f2021\/turtle-graphics\/","title":{"rendered":"Turtle Graphics"},"content":{"rendered":"\n

“Turtle Graphics<\/a>“ is a conceptual model for teaching computational thinking, based on a “first-person cursor”. In this schema, developed in the 1960s by computer scientist and constructivist educator Seymour Papert<\/a>, and inspired by Jean Piaget<\/a>‘s studies of children’s learning and embodied cognition, vector graphics are produced using a relative cursor (the “turtle”) upon a Cartesian plane.<\/p>\n

The Turtle object has the following methods or API (application programmer’s interface):<\/p>\n

\/\/ makeTurtle(x, y) -- make a turtle at x, y, facing right, pen down\r\n\/\/ left(d) -- turn left by d degrees\r\n\/\/ right(d) -- turn right by d degrees\r\n\/\/ forward(p) -- move forward by p pixels\r\n\/\/ back(p) -- move back by p pixels\r\n\/\/ penDown() -- pen down\r\n\/\/ penUp() -- pen up\r\n\/\/ goto(x, y) -- go straight to this location\r\n\/\/ setColor(color) -- set the drawing color\r\n\/\/ setWeight(w) -- set line width to w\r\n\/\/ face(d) -- turn to this absolute direction in degrees\r\n\/\/ angleTo(x, y) -- what is the angle from my heading to location x, y?\r\n\/\/ turnToward(x, y, d) -- turn by d degrees toward location x, y\r\n\/\/ distanceTo(x, y) -- how far is it to location x, y?<\/pre>\n
And here is the actual Turtle Graphics implementation for p5.js:<\/p>\n
function turtleLeft(d) {\r\n    this.angle -= d;\r\n}\r\n\r\n\r\nfunction turtleRight(d) {\r\n    this.angle += d;\r\n}\r\n\r\n\r\nfunction turtleForward(p) {\r\n    var rad = radians(this.angle);\r\n    var newx = this.x + cos(rad) * p;\r\n    var newy = this.y + sin(rad) * p;\r\n    this.goto(newx, newy);\r\n}\r\n\r\n\r\nfunction turtleBack(p) {\r\n    this.forward(-p);\r\n}\r\n\r\n\r\nfunction turtlePenDown() {\r\n    this.penIsDown = true;\r\n}\r\n\r\n\r\nfunction turtlePenUp() {\r\n    this.penIsDown = false;\r\n}\r\n\r\n\r\nfunction turtleGoTo(x, y) {\r\n    if (this.penIsDown) {\r\n      stroke(this.color);\r\n      strokeWeight(this.weight);\r\n      line(this.x, this.y, x, y);\r\n    }\r\n    this.x = x;\r\n    this.y = y;\r\n}\r\n\r\n\r\nfunction turtleDistTo(x, y) {\r\n    return sqrt(sq(this.x - x) + sq(this.y - y));\r\n}\r\n\r\n\r\nfunction turtleAngleTo(x, y) {\r\n    var absAngle = degrees(atan2(y - this.y, x - this.x));\r\n    var angle = ((absAngle - this.angle) + 360) % 360.0;\r\n    return angle;\r\n}\r\n\r\n\r\nfunction turtleTurnToward(x, y, d) {\r\n    var angle = this.angleTo(x, y);\r\n    if (angle < 180) {\r\n        this.angle += d;\r\n    } else {\r\n        this.angle -= d;\r\n    }\r\n}\r\n\r\n\r\nfunction turtleSetColor(c) {\r\n    this.color = c;\r\n}\r\n\r\n\r\nfunction turtleSetWeight(w) {\r\n    this.weight = w;\r\n}\r\n\r\n\r\nfunction turtleFace(angle) {\r\n    this.angle = angle;\r\n}\r\n\r\n\r\nfunction makeTurtle(tx, ty) {\r\n    var turtle = {x: tx, y: ty,\r\n                  angle: 0.0, \r\n                  penIsDown: true,\r\n                  color: color(128),\r\n                  weight: 1,\r\n                  left: turtleLeft, right: turtleRight,\r\n                  forward: turtleForward, back: turtleBack,\r\n                  penDown: turtlePenDown, penUp: turtlePenUp,\r\n                  goto: turtleGoTo, angleto: turtleAngleTo,\r\n                  turnToward: turtleTurnToward,\r\n                  distanceTo: turtleDistTo, angleTo: turtleAngleTo,\r\n                  setColor: turtleSetColor, setWeight: turtleSetWeight,\r\n                  face: turtleFace};\r\n    return turtle;\r\n}<\/pre>\n
Turtle Example 1\n
\n<\/h2><\/h2>
Here is an example using Turtle Graphics. Note that in order to post such code on WordPress, the entire Turtle object code must be included into your p5.js sketch file. Note that the Turtle code has been “minified” to save space.<\/p>\n
turtle-ex1<\/a>