Method update

src/main/java/trace/simulation/Boids.kt:16–30

    var important = mutableSetOf<Boid>()

    fun update(scale: Double) {
        val next = mutableListOf<Boid>()

        ArrayList(all).forEach {

            val n = propagate(it, all, scale)
            if (n != null) {
                next.add(n)
            }
        }

        all = next
        important.clear()

    }

    fun addBoid(at: Vec2, heading: Vec2) {
        all.add(Boid(at, heading.safeNormalize()))