var Boid = function ( x, y, angle ) {
    this.x = x;
    this.y = y;

    this.angle = Math.pow( Math.random(), 20 ) + angle;
    this.dx = Math.cos( this.angle );
    this.dy = Math.sin( this.angle );

    this.life = Math.random() * 100 + 100;
    this.dead = false;

    this.update = function () {

	    context.strokeStyle = '#808080';
	    context.beginPath();
	    context.moveTo( this.x, this.y );

	    this.x += this.dx * 2;
	    this.y += this.dy * 2;
	    this.life -= 1;

	    context.lineTo( this.x, this.y );
	    context.stroke();

	    var index = ( Math.floor( this.x ) + width * Math.floor( this.y ) ) * 4;

	    if ( this.life <= 0 ) this.kill();
	    if ( data[ index + 3 ] > 0 ) this.kill();

	    if ( this.x < 0 || this.x > width ) this.kill();						
	    if ( this.y < 0 || this.y > height ) this.kill();

    }

    this.kill = function () {

	    boids.splice( boids.indexOf( this ), 1 );
	    this.dead = true;

    }

}

var width = window.innerWidth;
var height = window.innerHeight;

var canvas = document.getElementById( 'world' );
canvas.width = width;
canvas.height = height;

var context = canvas.getContext( '2d' );
var image, data;

var boids = [];
boids.push( new Boid( width / 2, height / 2, Math.random() * 180 * Math.PI / 180 ) );

setInterval( function () {

    image = context.getImageData( 0, 0, width, height );
    data = image.data;

    for ( var i = 0; i < boids.length; i ++ ) {

	    var boid = boids[ i ];
	    boid.update();

	    if ( !boid.dead && Math.random() > 0.5 && boids.length < 500 ) {

		    boids.push( new Boid( boid.x, boid.y, ( Math.random() > 0.5 ? 90 : - 90 ) * Math.PI / 180 + boid.angle ) );

	    }

    }

}, 1000 / 60 );