And the algorithms to solve these quickly is another deep area of research.
In no particular order:
- the original boids code didn't cap the magnitude of acceleration after adding all the contributions; it added the contributions _by priority_, starting with separation, and if the max acceleration was exceeded it didn't add the others
- the max acceleration was decided by adding the _magnitudes_ not vectors of components, so the cohesion vector and the separation vector wouldn't cancel out - separation would win. I think this is why both this and the p5js one form very tight clumps which later "explode". That's this bit of the code (from https://www.red3d.com/cwr/code/boids.lisp):
;;
;; Available-acceleration should probably be 1.0, but I've set it a little higher to
;; avoid have to readjust the weighting factors for all of the acceleration requests.
;;
(vlet* ((composite-acceleration (prioritized-acceleration-allocation 1.3 ;; 1.0
avoid-obstacles
avoid-flockmates
velocity-matching
centering-urge
migratory-urge
course-leveling
course-damping))
- the original had different radii for different components (the separation threshold was 4, the cohesion, alignment thresholds were 5)
- both the clojure and p5js versions use the same strength for cohesion, separation, and alignment. In the original, separation is much stronger (1, vs 0.3 for cohesion and 0.23 for alignment). Again this might explain the tight clumps.
I've not yet mucked with the rules to see if the behaviour recovers, but the p5js version makes it easy to hack on https://editor.p5js.org/pattvira/sketches/v_tmN-BC5 - as a first change, in draw() in sketch.js change the print statement to this:
print(frameRate(), boids.length);
if (frameRate()>50) {
boids.push(new Boid(random(width), random(height)));
} else if (frameRate() < 40) {
boids.pop()
}
Aside: both the p5 and clojure versions do preserve the typo of 'seperation' from the Craig Reynold's code tho ;) ... I have to wonder if that's like 'referer' and now we have to spell it that way in a boids context.
The reason that the flocks are tight is because the separation "force" is normally computed as a repulsion between a target boid and all other nearby boids individually, not vs. the center of mass of all nearby boids.