Wednesday, April 16, 2014

Checking performance in EaselJS apps

So one of the great things about EaselJS is the fact that you can create Flash like games in JavaScript. I have been doing so on www.activememory.com for the last couple of years.

Unfortunately, it came to our attention that on some systems, the games ran rather slowly. According to their own docs, they admit that the time between ticks might be greater than specified because of CPU load (http://www.createjs.com/Docs/EaselJS/classes/Ticker.html#method_setInterval).

So, is there any way we can track the actual time between ticks on a real system?

Fortunately, yes, we can.

On each element that uses the ticker, you can set up an addEventListener and set the method you want to fire on that interval.

createjs.Ticker.addEventListener('tick', tickListener);

In the method itself you will want a few instance (or global) variables

this.previousFrameTime
this.totalFrames
this.totalFrameTimes

as well as a local variable

currentFrameTime

On each tick, we get the current timestamp (new Date() in JavaScript) and compare it to the previous.

We can then store the total number of ticks in the game, and then compare it to the total amount of time between frames.

This will give you the average frame time.

But enough of my yakking, here is a code sample (adapted from my code)

createjs.Ticker.setFPS(50);

Theatre = function() {
  var me = this; //set scope to this object
  var canvas = $('#canvas').get(0); // get the canvas object
  me.stage = new createjs.Stage(me.canvas); // create a stage object

  me.previousFrameTime = null; // initially null
  me.totalFrames = 0;
  me.totalFrameTimes = 0;

  createjs.Ticker.addEventListener('tick', me.tickListener);
}

Theatre.prototype.tickListener = function(event) {
  var me = this;
  var currentFrameTime = new Date();
  
  // skip the first frame because we haven't set a previousFrameTime yet
  if (me.previousFrameTime) {
    me.totalFrames++;
    me.totalFrameTimes += currentFrameTime - me.previousFrameTime;
  }

  me.previousFrameTime = currentFrameTime; // save this for the next tick
  me.stage.update(); // update the stage with each tick
}

// something else calls this when the game ends
Theatre.prototype.finish = function() {
  var me = this;
  console.log("average frame time in milliseconds:" + (me.totalFrameTimes / me.totalFrames);
}

So when you subtract 2 dates in JavaScript, it returns the difference in milliseconds.

If your FPS is 50, then you should have values that are round about 20 (1000 / 50 = 20). Anything much larger is an indication that your game is running much more slowly than it should be.