function $i(t) {

    return document.getElementById(t)

}

function $r(t, r) {

    document.getElementById(t).removeChild(document.getElementById(r))

}

function $t(t) {

    return document.getElementsByTagName(t)

}

function $c(t) {

    return String.fromCharCode(t)

}

function $h(t) {

    return ("0" + Math.max(0, Math.min(255, Math.round(t))).toString(16)).slice(-2)

}

function _i(t, r) {

    $t("div")[t].innerHTML += r

}

function _h(t) {

    return hires ? Math.round(t / 2) : t

}

function get_screen_size() {

    var t = document.documentElement.clientWidth,

        r = document.documentElement.clientHeight;

    return Array(t, r)

}

function init() {

    for (var t = 0; n > t; t++) star[t] = new Array(5), star[t][0] = Math.random() * w * 2 - 2 * x, star[t][1] = Math.random() * h * 2 - 2 * y, star[t][2] = Math.round(Math.random() * z), star[t][3] = 0, star[t][4] = 0;

    var r = $i("starfield");

    r.style.position = "absolute", r.width = w, r.height = h, context = r.getContext("2d"), context.fillStyle = "rgb(0,0,0)", context.strokeStyle = "rgb(255,255,255)"

}

function anim() {

    mouse_x = cursor_x - x, mouse_y = cursor_y - y, context.fillRect(0, 0, w, h);

    for (var t = 0; n > t; t++) test = !0, star_x_save = star[t][3], star_y_save = star[t][4], star[t][0] += mouse_x >> 4, star[t][0] > x << 1 && (star[t][0] -= w << 1, test = !1), star[t][0] < -x << 1 && (star[t][0] += w << 1, test = !1), star[t][1] += mouse_y >> 4, star[t][1] > y << 1 && (star[t][1] -= h << 1, test = !1), star[t][1] < -y << 1 && (star[t][1] += h << 1, test = !1), star[t][2] -= star_speed, star[t][2] > z && (star[t][2] -= z, test = !1), star[t][2] < 0 && (star[t][2] += z, test = !1), star[t][3] = x + star[t][0] / star[t][2] * star_ratio, star[t][4] = y + star[t][1] / star[t][2] * star_ratio, star_x_save > 0 && w > star_x_save && star_y_save > 0 && h > star_y_save && test && (context.lineWidth = 2 * (1 - star_color_ratio * star[t][2]), context.beginPath(), context.moveTo(star_x_save, star_y_save), context.lineTo(star[t][3], star[t][4]), context.stroke(), context.closePath());

    timeout = setTimeout("anim()", fps)

}

function start() {

    resize(), anim()

}

function resize() {

    w = parseInt(-1 != url.indexOf("w=") ? url.substring(url.indexOf("w=") + 2, -1 != url.substring(url.indexOf("w=") + 2, url.length).indexOf("&") ? url.indexOf("w=") + 2 + url.substring(url.indexOf("w=") + 2, url.length).indexOf("&") : url.length) : get_screen_size()[0]), h = parseInt(-1 != url.indexOf("h=") ? url.substring(url.indexOf("h=") + 2, -1 != url.substring(url.indexOf("h=") + 2, url.length).indexOf("&") ? url.indexOf("h=") + 2 + url.substring(url.indexOf("h=") + 2, url.length).indexOf("&") : url.length) : get_screen_size()[1]), x = Math.round(w / 2), y = Math.round(h / 2), z = (w + h) / 2, star_color_ratio = 1 / z, cursor_x = x, cursor_y = y, init()

}

var url = document.location.href,

    flag = !0,

    test = !0,

    n = parseInt(-1 != url.indexOf("n=") ? url.substring(url.indexOf("n=") + 2, -1 != url.substring(url.indexOf("n=") + 2, url.length).indexOf("&") ? url.indexOf("n=") + 2 + url.substring(url.indexOf("n=") + 2, url.length).indexOf("&") : url.length) : 812),

    w = 0,

    h = 0,

    x = 0,

    y = 0,

    z = 0,

    star_color_ratio = 0,

    star_x_save, star_y_save, star_ratio = 115,

    star_speed = 5,

    star_speed_save = 0,

    star = new Array(n),

    color, opacity = .1,

    cursor_x = 0,

    cursor_y = 0,

    mouse_x = 0,

    mouse_y = 0,

    canvas_x = 0,

    canvas_y = 0,

    canvas_w = 0,

    canvas_h = 0,

    context, key, ctrl, timeout, fps = 0;

start();

* {

  background:black;

  padding:0;

  margin:0;

}

canvas {

  padding:0;

  margin:0;

  width:100%;

  height:100%;

}

<canvas id="starfield"></canvas>