Dan Shiffman’s Processing Flocking Sketch in Clojure

This a port of Dan Shiffman’s Processing Flocking example ported to Clojure.

(defn separation
  [boid boids]
  (let [dsep     25.0
        filtered (separation-map boid (distance-filter boids 0.0 dsep))]
    (if-let [sum (reduce sum filtered)]
      (vm/div sum (count filtered))
      zero)))

versus:

PVector separate (ArrayList boids) {
  float desiredseparation = 25.0;
  PVector sum = new PVector(0,0,0);
  int count = 0;
  // For every boid in the system, check if it's too close
  for (int i = 0 ; i < boids.size(); i++) {
    Boid other = (Boid) boids.get(i);
    float d = loc.dist(other.loc);
    // If the distance is greater than 0 and less than an arbitrary amount (0 when you are yourself)
    if ((d > 0) && (d < desiredseparation)) {
      // Calculate vector pointing away from neighbor
      PVector diff = loc.sub(loc,other.loc);
      diff.normalize();
      diff.div(d);        // Weight by distance
      sum.add(diff);
      count++;            // Keep track of how many
    }
  }
  // Average -- divide by how many
  if (count > 0) {
    sum.div((float)count);
  }
  return sum;
}