// Basic turtle graphics implementation:

// https://en.wikipedia.org/wiki/Turtle_graphics

// For more info on Javascript OOP:

// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Introduction_to_Object-Oriented_JavaScript

//

// The turtle's coordinate system uses pixels for distance and degrees for rotations

// 0 degrees is straight right (east); positive degrees are clockwise

​

// Turtle constructor

// takes optional x, y starting coordinates (default is center of sketch)

function Turtle(x, y, pg) {

  // assign default values to x and y if they were not passed

  if (typeof x === "undefined") {

    x = width * 0.5;

  }

  if (typeof y === "undefined") {

    y = height * 0.5;

  }

  this.x = x;

  this.y = y;

  this.bearingRadians = 0;

  this.isPenDown = true;

  this._stateStack = [];

  this.pg = pg;

}

​

// moveTo instantly transports the turtle to the provided x, y location, drawing a line if pen is down

Turtle.prototype.moveTo = function (newX, newY) {

  let adjustedX = newX;

  if( adjustedX >= width ){

    adjustedX = width;

  }else if( adjustedX <= 0 ){

    adjustedX = 0;

  }

  let adjustedY = newY;

  if( adjustedY >= height ){

    adjustedY = height;

  }else if( adjustedY <= 0 ){

    adjustedY = 0;

  }

  if (this.isPenDown) {

    if( this.pg ){

      this.pg.line(this.x, this.y, adjustedX, adjustedY);

    }else{

      line(this.x, this.y, adjustedX, neadjustedYwY);

    }

  }

  this.x = adjustedX;

  this.y = adjustedY;

};

​

// moveForward moves the turtle along its current bearing, drawing a line if pen is down

Turtle.prototype.moveForward = function (distance) {

  var newX = this.x + cos(this.bearingRadians) * distance;

  var newY = this.y + sin(this.bearingRadians) * distance;

  this.moveTo(newX, newY);

};

​

// moveBackward moves the turtle backward from its current bearing, drawing a line if pen is down

Turtle.prototype.moveBackward = function (distance) {

  this.moveForward(-distance);

};

​

// turnTo changes the turtle's bearing to the provided angle in degrees

Turtle.prototype.turnTo = function (angleDegrees) {

  this.bearingRadians = radians(angleDegrees);

};

​

// turnRight rotates the turtle's bearing clockwise by the provided angle in degrees

Turtle.prototype.turnRight = function (amountDegrees) {

  this.bearingRadians += radians(amountDegrees);

};

​

// turnLeft rotates the turtle's bearing counter-clockwise by the provided angle in degrees

Turtle.prototype.turnLeft = function (amountDegrees) {

  this.bearingRadians -= radians(amountDegrees);

};

​

// penUp tells the turtle to move without drawing

Turtle.prototype.penUp = function () {

  this.isPenDown = false;

};

​

// penDown tells the turtle to draw a line when it moves

Turtle.prototype.penDown = function () {

  this.isPenDown = true;

};

​

// pushState records the turtle's current state (position, bearing, etc.) to a stack so that changes can be undone easily

Turtle.prototype.pushState = function () {

  this._stateStack.push({

    x: this.x,

    y: this.y,

    bearingRadians: this.bearingRadians,

    isPenDown: this.isPenDown,

  });

};

​

// popState restores the turtle's state to the top recorded state on the stack

Turtle.prototype.popState = function () {

  if (this._stateStack.length === 0) {

    console.error(

      "Turtle: No states left on stack. Make sure your calls to .pushState and .popState are balanced."

    );

    return;

  }

  var state = this._stateStack.pop();

  this.x = state.x;

  this.y = state.y;

  this.bearingRadians = state.bearingRadians;

  this.isPenDown = state.isPenDown;

};

​

// image draws and image centered on the turtle's current location and alligned with the turtle's rotation (forward = up)

Turtle.prototype.image = function (i, w, h, pg) {

  // w, h are optional parameters to this function and to p5's image

  // p5's image function will draw the image at its "normal" size if w and h are undefined

  if( pg ){

    pg.push();

    pg.translate(this.x, this.y);

    pg.rotate(this.bearingRadians + PI * 0.5);

    pg.imageMode(CENTER);

    pg.image(i, 0, 0, w, h);

    pg.pop();

  }else{

    if( this.pg ){

      this.pg.push();

      this.pg.translate(this.x, this.y);

      this.pg.rotate(this.bearingRadians + PI * 0.5);

      this.pg.imageMode(CENTER);

      this.pg.image(i, 0, 0, w, h);

      this.pg.pop();

    }else{

      push();

      translate(this.x, this.y);

      rotate(this.bearingRadians + PI * 0.5);

      imageMode(CENTER);

      image(i, 0, 0, w, h);

      pop();

    }

  }

};