// The Nature of Code

// The Coding Train / Daniel Shiffman

// https://youtu.be/OxHJ-o_bbzs

// https://thecodingtrain.com/learning/nature-of-code/5.4-arrive.html

// https://editor.p5js.org/codingtrain/sketches/1eUnUQnwB

​

class Vehicle {

  constructor(x, y) {

    this.pos = createVector(x, y);

    this.vel = createVector(0, 0);

    this.acc = createVector(0, 0);

    this.maxSpeed = Infinity;

    this.maxForce = 1;

    this.r = 16;

  }

​

  evade(vehicle) {

    let pursuit = this.pursue(vehicle);

    pursuit.mult(-1);

    return pursuit;

  }

​

  pursue(vehicle) {

    let target = vehicle.pos.copy();

    let prediction = vehicle.vel.copy();

    prediction.mult(10);

    target.add(prediction);

    fill(0, 255, 0);

    circle(target.x, target.y, 16);

    return this.seek(target);

  }

​

  arrive(target) {

​

    var positionNextFrame = p5.Vector.add(this.pos, this.vel);

    var displacement = p5.Vector.sub(target, positionNextFrame);

    var distance = displacement.mag();

    // "ideal" is the square root, but better reaction to a moving

    // target can be achieved with a slightly higher number.

    // Try setting it slightly below to see why root = 2 is ideal

    var root = 2.15;

    var desiredSpeed = Math.pow(2 * this.maxForce * distance, 1 / root);

​

    // to avoid tiny oscillations

    if (distance < 2)

      desiredSpeed = 0.1 * distance;

    var force = p5.Vector.sub(displacement.setMag(desiredSpeed), this.vel);

    force.limit(this.maxForce);

    return force;

  }

​

  flee(target) {

    return this.seek(target).mult(-1);

  }

​

  seek(target) {

    let force = p5.Vector.sub(target, this.pos);

    var desiredSpeed = this.maxSpeed;

    force.setMag(desiredSpeed);

​

    force.sub(this.vel);

    force.limit(this.maxForce);

    return force;

  }

​

  applyForce(force) {

    this.acc.add(force);

  }

​

  update() {

    this.vel.add(this.acc);

    this.vel.limit(this.maxSpeed);

    this.pos.add(this.vel);

    this.acc.set(0, 0);

  }

​

  show() {

    stroke(255);

    strokeWeight(2);

    fill(255);

    push();

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

    rotate(this.vel.heading());

    triangle(-this.r, -this.r / 2, -this.r, this.r / 2, this.r, 0);

    pop();

  }

​

  edges() {

    if (this.pos.x > width + this.r) {

      this.pos.x = -this.r;

    } else if (this.pos.x < -this.r) {

      this.pos.x = width + this.r;

    }

    if (this.pos.y > height + this.r) {

      this.pos.y = -this.r;

    } else if (this.pos.y < -this.r) {

      this.pos.y = height + this.r;

    }

  }

}

​

class Target extends Vehicle {

  constructor(x, y) {

    super(x, y);

    this.vel = p5.Vector.random2D();

    this.vel.mult(5);

  }

​

  show() {

    stroke(255);

    strokeWeight(2);

    fill("#F063A4");

    push();

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

    circle(0, 0, this.r * 2);

    pop();

  }

}

​