Birds, slowly

I’ve wanted for a while to write a bird flocking simulation, and am finally actually doing so.


This is, unsurprisingly, something a bunch of people have done previously. The most famous example is boids, a simple flocking model created by Craig Reynolds, consisting of a handful of steering rules for individual birds that result in a creditable flock simulation.

The rules are:

Here, “local flockmates” is defined as “other birds within some radius of the steering bird, excluding a blind-spot behind the steering bird”. So the calculation for each bird only involves a subset of the birds comprising the entire flock.

This produces some interesting stuff, but it’s still only a pale approximation of starling murmurations. It’s almost certainly an act of wild hubris to believe I can produce something as stunning as this, but it’s something to shoot for.

starling murmuration


Mostly I just like to look at starlings, so if I can get that on my computer I think that’d be pretty cool. There are some side benefits I’d like to get out of this, though:

and of course the #1 priority:

Previous attempts have faltered miserably because I tried to do all of this at once. Who doesn’t like to start a personal enjoyment project by learning about clojurescript build pipelines, the google closure compiler, vim REPL plugins and all that shit?

Oh, right, I don’t. This has reduced me to crying frustration.

I’ve therefore tried to break this down into achievable blobs, almost as if I were writing software, a thing I do professionally for money and mostly without crying.

  1. Implement boids in 2D, using JS and canvas
  2. Implement boids in 3D, using JS and webGL
  3. Rewrite the 2D version in clojurescript
  4. Rewrite the 3D version in clojurescript
  5. Do better than boids!

Most importantly, I’m going to ditch the hell out of 3 and 4 if they prove annoying.


So far I’m on step 1.

I’ve gone from being able to draw dots on a canvas…

20 dots moving in a straight line

…to some sort of stoner protective circle…

20 dots moving slowly in a ring

…to something that looks passably birdlike for a while…

20 dots moving slightly birdily

…but settles down into a very stable pattern quite quickly.

20 dots orbiting a central point

I’ve got the steering rules implemented, but haven’t done the “nearby flockmates” logic, so each bird considers every other bird when steering (I think this is why my simulation gets stable so quickly).

I’ll do a proper writeup of how this stuff works once I’ve got a 2D version I’m happy with, along with some source code. Mostly I’m posting this to give myself a sense of progress, which is also why I’m going to end it with an almost rude degree of abruptness.

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