let speed = 50;

let view_distance = 150;

​

function setup() {

  createCanvas(400, 400);

  let rangle;

  for (i = 0; i < 40; i++) {

    rangle = random(0, 2 * Math.PI);

    boids.push(new Boid(

      random(0, width),

      random(0, height),

      speed * Math.cos(rangle),

      speed * Math.sin(rangle)

    ));

  }

}

​

function draw() {

  background(220);

  boids.forEach(boid => boid.update());

  boids.forEach(boid => boid.draw());

  let lineStart = [boids[0].pos.x, boids[0].pos.y];

  let lineEnd = [boids[0].pos.x + boids[0].vel.x,

                 boids[0].pos.y + boids[0].vel.y];

  line(lineStart[0], lineStart[1], lineEnd[0], lineEnd[1]);

  noFill();

  circle(lineStart[0], lineStart[1], 150);

}

​

class Boid {

  constructor(initX, initY, initVX, initVY) {

    this.pos = createVector(initX, initY);

    this.vel = createVector(initVX, initVY);

  }

  update() {

    this.pos.add(this.new_pos(deltaTime / 1000));

    this.edge_check();

    this.stray_from_others();

  }

  draw() {

    push()

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

    rotate(this.vel.heading());

    noStroke();

    fill("#b00");

    triangle(-5, -5, -5, 5, 10, 0);

    pop()

  }

  edge_check() {

    let offset = 10

    if (this.pos.x < - offset) {

      this.pos.x += width + offset*2;

    }

    else if (this.pos.x > width + offset) {

      this.pos.x -= width + offset*2;

    }

    if (this.pos.y < -offset) {

      this.pos.y += height + offset*2;

    }

    else if (this.pos.y > height + offset) {

      this.pos.y -= height + offset*2;

    }

  }

  stray_from_others() {

    let dist_sq;

    for (var boid of boids) {

      let sep_vec = p5.Vector.sub(boid.pos, this.pos);

      dist_sq = sep_vec.magSq();

      if (dist_sq == 0) {

        continue

      }

      else if (dist_sq > view_distance**2) {

        continue

      }

      let dist_sq_inv = 1 / dist_sq**(0.7);

      let cross = p5.Vector.cross(this.vel, sep_vec);

      let direc = (cross.z < 0) ? 1: -1;

      this.vel.rotate(direc * dist_sq_inv * Math.PI / 2);

    }

  }

  new_pos(dt) {

    return p5.Vector.mult(this.vel, dt);

  }

}