boids/boids.mjs

import {Vector} from './geometry.mjs';

// Outline of the shape of a boid when angled at 0 rad
const boidShape = [
    new Vector(1, 0),
    new Vector(-.5, .5),
    new Vector(-.5, -.5),
    new Vector(1, 0),
];
const boidShapeLength = boidShape.length;

class Boid
{
    constructor(params, center)
    {
        this.params = params;
        this.pos = center.clone();
        this.vel = new Vector(Math.random() - 0.5, Math.random() - 0.5);
        this.register = new Vector(0, 0);
    }

    draw(ctx)
    {
        const transformed = this.register;
        const angle = this.vel.angle();
        let isFirst = true;

        for (let j = 0; j < boidShapeLength; ++j)
        {
            transformed.x = boidShape[j].x;
            transformed.y = boidShape[j].y;
            transformed.rotate(angle).mul(this.params.radius).add(this.pos);

            if (isFirst)
            {
                ctx.moveTo(transformed.x, transformed.y);
                isFirst = false;
            }
            else
            {
                ctx.lineTo(transformed.x, transformed.y);
            }
        }
    }
}

class Boids
{
    constructor(canvas, params = {})
    {
        this.canvas = canvas;
        this.ctx = canvas.getContext('2d');

        this.params = Object.assign({
            centerAccel: 0.075,
            repelAccel: 0.8,
            matchAccel: 0.15,
            boundsAccel: 0.01,

            maxSpeed: 300,

            closeDist: 20,
            visibleDist: 60,

            radius: 10,
            color: 'black',
            debug: false,
        }, params);

        // Current width and height of the canvas
        this.width = canvas.width;
        this.height = canvas.height;

        // Current center point of the canvas
        this.center = null;

        // Last time where the canvas was repainted
        this.lastTime = null;

        // List of active simulated boids
        this.boids = [];

        // List of obstacles
        this.obstacles = [];

        // Vector registers used for holding temporary values
        this.registers = [
            new Vector(0, 0),
            new Vector(0, 0),
            new Vector(0, 0)
        ];

        // When the simulation is running, the ID of the next rAF request,
        // otherwise, null
        this.animationId = null;

        this._afterResize();
    }

    /** Change the canvas’ dimensions */
    resize(width, height)
    {
        this.canvas.width = width;
        this.canvas.height = height;

        this.width = width;
        this.height = height;

        this._afterResize();
    }

    _afterResize()
    {
        this.center = new Vector(this.width / 2, this.height / 2);
        this.ctx.resetTransform();
        this.ctx.translate(this.center.x, this.center.y);
    }

    /** Introduce a new boid in the simulation. */
    add(center)
    {
        this.boids.push(new Boid(this.params, center));
    }

    /** Start the simulation. */
    start()
    {
        if (this.animationId !== null)
        {
            return;
        }

        this._step = this._step.bind(this);
        this.animationId = requestAnimationFrame(this._step);
    }

    /** Pause the simulation. */
    pause()
    {
        cancelAnimationFrame(this.animationId);
        this.animationId = null;
        this.lastTime = null;
    }

    /**
     * @private
     * Perform a time step of the simulation and update the canvas.
     */
    _step(time)
    {
        if (!this.lastTime)
        {
            this.lastTime = time;
        }

        const delta = (time - this.lastTime) / 1000;
        this.lastTime = time;

        this._update(delta);
        this._draw();

        if (this.animationId !== null)
        {
            this.animationId = requestAnimationFrame(this._step);
        }
    }

    /**
     * @private
     * Advance the simulation.
     */
    _update(delta)
    {
        const boidsLength = this.boids.length;
        const obstaclesLength = this.obstacles.length;

        for (let i = 0; i < boidsLength; ++i)
        {
            const me = this.boids[i];

            const meanPos = this.registers[0].reset();
            const meanVel = this.registers[1].reset();
            const repelForce = this.registers[2].reset();

            let visibles = 0;

            // Compute mean flock position and velocity and compute
            // the repel force from other boids
            for (let j = 0; j < boidsLength; ++j)
            {
                if (i != j)
                {
                    const you = this.boids[j];
                    const dist = Vector.distSquared(me.pos, you.pos);

                    if (dist < this.params.visibleDist
                             * this.params.visibleDist)
                    {
                        meanPos.add(you.pos);
                        meanVel.add(you.vel);
                        visibles += 1;

                        if (dist < this.params.closeDist
                                 * this.params.closeDist)
                        {
                            repelForce.add(me.pos).sub(you.pos);
                        }
                    }
                }
            }

            // Compute the repel force from obstacles
            for (let j = 0; j < obstaclesLength; ++j)
            {
                const obstacle = this.obstacles[j];

                if (obstacle.distance(me.pos) < this.params.closeDist)
                {
                    me.vel.add(me.pos).sub(obstacle.center);
                }
            }

            // Attract towards center of visible flock
            if (visibles >= 1)
            {
                me.vel.add(meanPos.div(visibles)
                                  .sub(me.pos)
                                  .mul(this.params.centerAccel));
            }

            // Attract toward center of screen if out of bounds
            if (me.pos.x < this.width * -.4
                    || me.pos.x > this.width * .4
                    || me.pos.y < this.height * -.4
                    || me.pos.y > this.height * .4)
            {
                me.vel.addMul(me.pos, -this.params.boundsAccel);
            }

            // Repel away from close boids
            me.vel.add(repelForce.mul(this.params.repelAccel));

            // Match other boids’ velocity
            if (visibles >= 1)
            {
                me.vel.add(meanVel.div(visibles)
                                  .sub(me.vel)
                                  .mul(this.params.matchAccel));
            }

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

            if (speed > this.params.maxSpeed * this.params.maxSpeed)
            {
                me.vel.div(Math.sqrt(speed)).mul(this.params.maxSpeed);
            }

            // Integrate speed
            me.pos.addMul(me.vel, delta);
        }
    }

    /**
     * @private
     * Redraw the boids.
     */
    _draw()
    {
        const boidsLength = this.boids.length;
        const obstaclesLength = this.obstacles.length;

        this.ctx.clearRect(
            -this.width / 2, -this.height / 2,
            this.width, this.height
        );

        // Draw obstacles
        if (this.params.debug)
        {
            this.ctx.fillStyle = '#dddddd';
            this.ctx.beginPath();

            for (let i = 0; i < obstaclesLength; ++i)
            {
                this.obstacles[i].draw(this.ctx);
            }

            this.ctx.fill();
        }

        // Draw boids
        this.ctx.fillStyle = this.params.color;
        this.ctx.beginPath();

        for (let i = 0; i < boidsLength; ++i)
        {
            this.boids[i].draw(this.ctx);
        }

        this.ctx.fill();
    }
}

export default Boids;