boids/boids.mjs

import Vector from './vector.mjs';

const findNeighbors = (boids, boid, radius) =>
{
    const neighbors = [];

    for (let otherBoid of boids)
    {
        if (boid != otherBoid)
        {
            const dist = boid.pos.sub(otherBoid.pos).normSquared();

            if (dist < radius * radius)
            {
                neighbors.push(otherBoid);
            }
        }
    }

    return neighbors;
};

export const update = (boids, params, time) =>
{
    for (let boid of boids)
    {
        const visible = findNeighbors(boids, boid, params.visibleDist);
        const close = findNeighbors(boids, boid, params.closeDist);

        // Attract towards center of visible flock
        const center = new Vector(0, 0);

        for (let otherBoid of visible)
        {
            center.addMut(otherBoid.pos);
        }

        if (visible.length >= 1)
        {
            center.divMut(visible.length);
            boid.vel.addMut(center.sub(boid.pos).mul(params.centerAccel));
        }

        // Attract toward center of screen
        boid.vel.addMut(boid.pos.mul(-0.01));

        // Repel away from close boids
        for (let otherBoid of close)
        {
            boid.vel.addMut(boid.pos
                .sub(otherBoid.pos)
                .mul(params.repelAccel));
        }

        // Match other boids’ velocity
        const velocity = new Vector(0, 0);

        for (let otherBoid of visible)
        {
            velocity.addMut(otherBoid.vel);
        }

        if (visible.length >= 1)
        {
            velocity.divMut(visible.length);
            boid.vel.addMut(velocity.sub(boid.vel).mul(params.matchAccel));
        }

        // Do not surpass maximum speed
        const speed = boid.vel.normSquared();

        if (speed > params.maxSpeed * params.maxSpeed)
        {
            boid.vel.divMut(Math.sqrt(speed)).mulMut(params.maxSpeed);
        }

        boid.pos.addMut(boid.vel.mul(time));
    }
};