// Every particle moves to get closer to one other particle and

// farther than one other particle. They also slowly make their

// way to the centre of the sketch.

​

let avoid_mult = 1.001;

let decay_mult = 0.15;

let N = 3000;

​

let particles;

​

function unitDiff(Q, P) {

  const dx = Q.x - P.x;

  const dy = Q.y - P.y;

  const d = sqrt(dx * dx + dy * dy);

  if (d < 1e-7) {

    return { x: 0, y: 0 };

  } else {

    return { x: dx / d, y: dy / d, d: d };

  }

}

​

function initParticles(n) {

  //avoid_mult = random( 1, 1.1 );

  //decay_mult = random( 0.1, 0.2 );

​

  particles = [];

  for (let idx = 0; idx < n; ++idx) {

    const ang = random(TWO_PI);

    let rad = random(1);

    rad = 30 * rad * rad;

​

    let att = int(random(n));

    while (att == idx) {

      att = int(random(n));

    }

    let avo = int(random(n));

    while (avo == idx) {

      avo = int(random(n));

    }

    particles.push({

      x: width / 2 + rad * cos(ang),

      y: height / 2 + rad * sin(ang),

      attract: att,

      avoid: avo,

      v: random(100, 255),

    });

  }

}

​

function tick() {

  for (let idx = 0; idx < particles.length; ++idx) {

    const p = particles[idx];

    p.a = { x: 0, y: 0 };

    if (p.attract != idx) {

      const v = unitDiff(particles[p.attract], p);

      const dd = min(1, v.d);

      p.a.x += dd * v.x;

      p.a.y += dd * v.y;

    }

    if (p.avoid != idx) {

      const v = unitDiff(p, particles[p.avoid]);

      p.a.x += v.x * avoid_mult;

      p.a.y += v.y * avoid_mult;

    }

​

    // const theta = frameCount * 0.001;

    // const c = { x : width/2 + 100 * cos( theta ), y : height/2 + 100 * sin( theta ) };

​

    const c = { x: width / 2, y: height / 2 };

    const v = unitDiff(c, p);

    p.a.x += v.x * decay_mult;

    p.a.y += v.y * decay_mult;

  }

  for (let idx = 0; idx < particles.length; ++idx) {

    const p = particles[idx];

    p.x += p.a.x;

    p.y += p.a.y;

  }

}

​

function setup() {

  createCanvas(600, 600);

  initParticles(N);

}

​

function draw() {

  background(5, 5, 80);

​

  noStroke();

​

  for (let idx = 0; idx < 20; ++idx) {

    tick();

  }

  for (let p of particles) {

    fill(255, 255, p.v, 150);

    ellipse(p.x, p.y, 4, 4);

  }

}

​

function keyPressed() {

  if (key === "s") {

    save("jan1.png");

  }

}

​