Using requestAnimationFrame and a target FPS

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Combining setInterval and requestAnimationFrame to get a target framerate

In the beginning...

People who've worked with Javascript animations before will probably know the next piece of code:
var targetFps = 25;
var loopInterval = window.setInterval(renderFrame, 1000 / targetFps);

What this does is create a loop that will run 25 times per second, which will hopefully give you your target framerate of 25 frames per second.

And They said: Do not use setInterval!

But then the powers that be thought of a new api: requestAnimatonFrame. It's basically a function that tells the browser it needs to execute something which will result in a redraw of a certain element.

We were told to set it up in a function like this:

function renderLoop(){
    // Put another iteration of renderLoop in the animation queue
    // Actually calculate and draw a frame

Yes, you're reading it correctly: it's basically a function calling itself. This will give you the best possible framerate. But what if we could combine those 2: setInterval and requestAnimationFrame?

The best of both worlds

function renderLoop(){

    var targetFps = 25;	
    // Combine setInterval and requestAnimationFrame in order to get a desired fps
    setInterval(function() {
    }, 1000 / targetFps);

And now you have a working requestAnimationFrame setup with a target fps!

So, what do you think?

A requestAnimationFrame polyfill

Warning: you will probably want to use a fallback function. Current fallback functions default to setInterval itself, which is not what we want.

Here's a very basic one you can use:

window.requestAnimFrame = (function(){
  return  window.requestAnimationFrame       || 
		  window.webkitRequestAnimationFrame ||
		  window.mozRequestAnimationFrame    || 
		  window.oRequestAnimationFrame      || 
		  window.msRequestAnimationFrame     || 
		  function(/* function */ callback, /* DOMElement */ element){

			// Since our requestAnimFrame is already in a loop in order to
			// control the preferred FPS, just call callback, not an interval


This is also a well known problem in the professional video industry when you want to playback a video at a different FPS then the device showing it refresh at. Many techniques has been used such as frame blending and complex re-timing re-building intermediate frames based on motion vectors, but with canvas these techniques are not available and the result will always be jerky video.



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