boids

functional, data-oriented steering behaviors

why

I had trouble finding steering behaviors with the following properties:

• functional and data oriented
• doesn't create memory garbage
• re-uses a robust vector module rather than re-inventing the wheel

So here we are.

usage

import Boids    from 'https://cdn.jsdelivr.net/gh/mreinstein/boids/boids.js'
import { vec2 } from 'https://cdn.skypack.dev/pin/gl-matrix@v3.4.3-OSmwlRYK5GW1unkuAQkN/mode=imports,min/optimized/gl-matrix.js'


const position = [ 50, 50 ]

const b = {
    steering: Boids.createSteeringComponent()
    aabb: {
        width: 10,
        height: 10,
        position
    },
    transform: {
        position
    },
    rigidBody: {
        mass: 1,
        maxSpeed: 5, // the max length of the velocity vector
        smoothedAcceleration: [ 0, 0, ], // internal data structure used to smooth accel over time
        velocity: [ 0, 0 ]
    }
}

const steeringForce = vec2.create()


function drawBoid (b) {
    // omitted for brevity, draw the boid using whatever graphics API you're using here
}


function stepBoid (b) {
    // reset the steering force vector used every frame.
    vec2.set(steeringForce, 0, 0)

    // determine  steering forces
    Boids.steerForSeek(steeringForce, b, [ 300, 300 ])

    // determine the new velocity for the boid based on a steering force
    Boids.applySteeringForce(b, steeringForce)


    // Euler integrate (per frame) velocity into position
    vec2.add(boid.transform.position, boid.transform.position, boid.rigidBody.velocity)
}


function tick () {
    stepBoid(b)
    drawBoid(b)
    requestAnimationFrame(tick) 
}


requestAnimationFrame(tick)

The examples/ directory has runnable demos of all steering behaviors.

available steering behaviors

• steerForSeparation
• steerForAlignment
• steerForCohesion
• steerForSeparation
• steerForFlock
• steerForArrival
• steerForEvasion
• steerForFlee
• steerForFollowLeader
• steerForFollowPath
• steerForPursuit
• steerForQueueing
• steerForSeek
• steerForWander
• steerForCollisionAvoidance

inspiration

• http://www.red3d.com/cwr/steer/gdc99/ Craig Reynold's seminal work (original concept author)
• https://github.com/ianmcgregor/boid (high quality but object oriented javascript implementation)
• https://gamedevelopment.tutsplus.com/series/understanding-steering-behaviors--gamedev-12732