requestAnimationFrame at a limited framerate

Question

As I understand it, usage of the JS requestAnimationFrame API is intended for cases where the framerate isn\'t in need of being controlled, but I have a use cas

Answer 1

This is just a proof of concept.

All we do is set our frames per second and intervals between each frame. In the drawing function we deduct our last frame’s execution time from the current time to check whether the time elapsed since the last frame is more than our interval (which is based on the fps) or not. If the condition evaluates to true, we set the time for our current frame which is going to be the “last frame execution time” in the next drawing call.

var Timer = function(callback, fps){
  var now = 0;
  var delta = 0;
  var then = Date.now();

  var frames = 0;
  var oldtime = 0;

  fps = 1000 / (this.fps || fps || 60);

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

    now = Date.now();
    delta = now - then;

    if (delta > fps) {
      // Update time stuffs
      then = now - (delta % fps);

      // Calculate the frames per second.
      frames = 1000 / (time - oldtime)
      oldtime = time;

      // Call the callback-function and pass
      // our current frame into it.
      callback(frames);
    }
  });
};

Usage:

var set;
document.onclick = function(){
  set = true;
};

Timer(function(fps){
  if(set) this.fps = 30;
  console.log(fps);
}, 5);

http://jsfiddle.net/ARTsinn/rPAeN/