/*

limitLoop.js - limit the frame-rate when using requestAnimation frame
Released under an MIT license.

Why use it?
----------------
A consistent frame-rate can be better than a janky experience only 
occasionally hitting 60fps. Use this trick to target a specific frame-
rate (e.g 30fps, 48fps).

This type of trick works better when you know you have a fixed amount
of work to be done and it will always take longer than 16.6ms. It doesn't
work as well when your workload is somewhat variable.


Solution
----------------

When we draw, deduct the last frame's execution time from the current 
time to see if the time elapsed since the last frame is more than the 
fps-based interval or not. Should the condition evaluate to true, set 
the time for the current frame which will be the last frame execution 
time in the next drawing call.

Prior art / inspiration
------------------------
http://cssdeck.com/labs/embed/gvxnxdrh/0/output
http://codetheory.in/controlling-the-frame-rate-with-requestanimationframe/
*/

// rAF
window.requestAnimationFrame = function() {
    return window.requestAnimationFrame ||
		window.webkitRequestAnimationFrame ||
		window.mozRequestAnimationFrame ||
		window.msRequestAnimationFrame ||
		window.oRequestAnimationFrame ||
		function(f) {
			window.setTimeout(f,1e3/60);
		}
}();

var limitLoop = function (fn, fps) {

    var then = new Date().getTime();
    var oldtime = 0;
    
    // custom fps, otherwise fallback to 60
    fps = fps || 60;

    return (function loop(time) {
        requestAnimationFrame(loop);

        var interval = 1000 / (this.fps || fps);
        var now = new Date().getTime();
        var delta = now - then;

        if (delta > interval) {
            // Update time
            // now - (delta % interval) is an improvement over just 
            // using then = now, which can end up lowering overall fps
            then = now - (delta % interval);

            // calculate fps
            var frames = 1000 / (time - oldtime)
            oldtime = time;

            // call the fn, passing current fps to it
            fn(frames);
        }
    }(0));
};