// The Nature of Code

// The Coding Train / Daniel Shiffman

// https://youtu.be/Q4MU7pkDYmQ

// https://thecodingtrain.com/learning/nature-of-code/5.3-flee-pursue-evade.html

​

// Flee: https://editor.p5js.org/codingtrain/sketches/v-VoQtETO

// Pursue: https://editor.p5js.org/codingtrain/sketches/Lx3PJMq4m

// Evade: https://editor.p5js.org/codingtrain/sketches/X3ph02Byx

// Pursue Bouncing Ball: https://editor.p5js.org/codingtrain/sketches/itlyDq3ZB

// Pursue Wander: https://editor.p5js.org/codingtrain/sketches/EEnmY04lt

// Pursue Slider Prediction: https://editor.p5js.org/codingtrain/sketches/l7MgPpTUB

​

class Vehicle {

  constructor(x, y) {

    this.pos = createVector(x, y);

    this.vel = createVector(0, 0);

    this.acc = createVector(0, 0);

    this.maxSpeed = 5;

    this.maxForce = 0.25;

    this.r = 8;

  }

​

  evade(vehicle) {

    let pursuit = this.pursue(vehicle);

    pursuit.mult(-1);

    return pursuit;

  }

​

  pursue(vehicle) {

    // Use the Law of Sines (https://en.wikipedia.org/wiki/Law_of_sines)

    // to predict the right collision point

    const speed_ratio = vehicle.vel.mag() / this.maxSpeed;

    const target_angle = vehicle.vel.angleBetween(p5.Vector.sub(this.pos, vehicle.pos));

    const my_angle = asin(sin(target_angle) * speed_ratio);

    const dist = this.pos.dist(vehicle.pos);

    const prediction = dist * sin(my_angle) / sin(PI - my_angle - target_angle);

    const target = vehicle.vel.copy().setMag(prediction).add(vehicle.pos);

    drawArrow(vehicle.pos, p5.Vector.mult(vehicle.vel, 20), 'red');

    drawArrow(this.pos, p5.Vector.sub(target, this.pos), 'green');

    fill(0, 255, 0);

    circle(target.x, target.y, 8);

    return this.seek(target);

  }

​

  flee(target) {

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

  }

​

  seek(target) {

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

    force.setMag(this.maxSpeed);

    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(4);

  }

​

  show() {

    stroke(255);

    strokeWeight(2);

    fill("#F063A4");

    push();

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

    circle(0, 0, this.r * 2);

    pop();

  }

}

​