Plasma effect in javascript using canvas

plasma.js

(function() {

    var SCREEN_WIDTH  = window.innerWidth,
        SCREEN_HEIGHT = window.innerHeight,
        canvas        = document.getElementById('canvas'),
        context       = canvas.getContext('2d'),
        res           = 48,
        rad           = Math.PI / 180,
        aa = ab = ac = ad = 0,
        cr = cg = cb  = 128, // COLOR
        a             = seed(6),
        HALF_WIDTH    = Math.ceil(SCREEN_WIDTH / res),
        HALF_HEIGHT   = Math.ceil(SCREEN_HEIGHT / res);

    init();

    function init() {
        canvas.height = SCREEN_HEIGHT;
        canvas.width  = SCREEN_WIDTH;

        plasma();
    }

    function plasma() {

        for(var x = 0; x < res; x++) {

            aa += 0.0005 * Math.cos(rad * x * a[0]);
            ac += 0.0010 * Math.sin(rad * (res - x) * a[2]);

            for(var y = 0; y < res; y++) {

                ab += 0.001 * Math.cos(rad * y * a[1]);
                ad += 0.001 * Math.sin(rad * (res - y) * a[3]);

                var h = x * 8 * Math.sin(rad * (aa + ab) * a[4]),
                    j = y * 8 * Math.cos(rad * (ac + ad) * a[5]),
                    k = (x * a[0] + y * a[1]) * 32 * Math.sin(rad * ((res - x) * h + (y - res) * h) * a[2] / 720),
                    l = (res * a[3] - x  * a[3] + (res * a[4] - y * a[4])) * 32 * Math.sin(rad * (x * h + y * j) * a[5] / 720);

                h = 48 * Math.cos(rad * h) + 42 * Math.cos(rad * j);


                cr = 128 + Math.ceil(42 * Math.cos(rad * k) + h);
                cg = 128 + Math.ceil(42 * Math.cos(rad * l) + h);
                cb = Math.ceil((cr + cg) / 2 - h * 2);

                context.fillStyle = 'rgb(' + cr + ',' + cg + ',' + cb + ')';
                context.fillRect(y * HALF_WIDTH, x * HALF_HEIGHT, HALF_WIDTH, HALF_HEIGHT);

            }

        }

        setTimeout(plasma, 20);

    }

    function seed(count) {
        var res = [];
        for(var i = 0; i < count; i++) {
            res[i] = Math.ceil(Math.random(0, 1) * 3 + 1);
        }
        return res;
    }

})();