Snow Draw

javascript: var DrawLine = function () {

    var context, offsetLeft, offsetTop;

    function _drawCircle(mouseX, mouseY) {
        var x = mouseX - offsetLeft,
            y = mouseY - offsetTop;
        context.beginPath();
        context.arc(x, y, 15, 0, Math.PI * 2);
        context.closePath();
        context.fill();
    }

    function _setLineStyle() {
        context.strokeStyle = "#df4b26";
        context.lineJoin = "round";
        context.lineWidth = 20;
    }

    return {
        init: function (canvas) {
            var isPainting = false;

            context = canvas.getContext("2d"),
            offsetLeft = canvas.offsetLeft,
            offsetTop = canvas.offsetTop;

            var isMobile = +("ontouchstart" in window);

            var events = {
                start: ["mousedown", "touchstart"],
                end: ["mouseup", "touchend"],
                move: ["mousemove", "touchmove"]
            };

            canvas.addEventListener(events.start[isMobile], function (e) {
                isPainting = true;
                e = isMobile ? e.targetTouches[0] : e;
                _drawCircle(e.pageX, e.pageY);
            }, false);
            canvas.addEventListener(events.end[isMobile], function (e) {
                isPainting = false;
            }, false);
            canvas.addEventListener(events.move[isMobile], function (e) {
                if (isPainting) {
                    e = isMobile ? e.targetTouches[0] : e;
                    _drawCircle(e.pageX, e.pageY);
                }
            }, false);
        }
    }
}();
! function () {
    var canvas = document.createElement("canvas");
    canvas.width = window.outerWidth;
    canvas.height = window.outerHeight;
    canvas.style.position = "absolute";
    canvas.style.top = "0px";
    canvas.style.left = "0px";
    document.body.appendChild(canvas);

    var context = canvas.getContext("2d");

    context.globalAlpha = 0.8;
    context.fillStyle = "rgb(255, 255, 255)";
    context.fillRect(0, 0, canvas.width, canvas.height);

    context.globalCompositeOperation = "destination-out";

    DrawLine.init(canvas);
}();