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I am trying to compare performance for 3d applications on mobile devices. I have a 3d solar system set up in webGL and im trying to record or at least display the FPS. So far this is what i Have:

in the body

<script language="javascript">
var x, message;
x = Time;
message = "fps is equal to ";
document.write (message); // prints the value of the message variable
document.write (x); //prints the value of x
</script>

and to get The Time Var in the draw function of canvas i have this

var Time = 0;
function drawScene() {
var startTime = new Date();
//draw scene here
var endTime = new Date();
Time = (endTime - startTime)
}

the output i get at the bottom of the canvas is "fps is equal to null"

any help would be great!

I am trying to compare performance for 3d applications on mobile devices. I have a 3d solar system set up in webGL and im trying to record or at least display the FPS. So far this is what i Have:

in the body

<script language="javascript">
var x, message;
x = Time;
message = "fps is equal to ";
document.write (message); // prints the value of the message variable
document.write (x); //prints the value of x
</script>

and to get The Time Var in the draw function of canvas i have this

var Time = 0;
function drawScene() {
var startTime = new Date();
//draw scene here
var endTime = new Date();
Time = (endTime - startTime)
}

the output i get at the bottom of the canvas is "fps is equal to null"

any help would be great!

• javascript
• webgl

Share Improve this question Follow asked May 8, 2013 at 4:41 timtim 31911 gold badge55 silver badges1515 bronze badges 1

• 1 take a look at github.com/mrdoob/stats.js – gaitat Commented Nov 21, 2017 at 22:08

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5 Answers 5

Sorted by: Reset to default 19

Displaying FPSs is pretty simple and has really nothing to do with WebGL other than it's common to want to know. Here's a small FPS display

const fpsElem = document.querySelector("#fps");

let then = 0;
function render(now) {
  now *= 0.001;                          // convert to seconds
  const deltaTime = now - then;          // compute time since last frame
  then = now;                            // remember time for next frame
  const fps = 1 / deltaTime;             // compute frames per second
  fpsElem.textContent = fps.toFixed(1);  // update fps display
  
  requestAnimationFrame(render);
}
requestAnimationFrame(render);

<div>fps: <span id="fps"></span></div>

Use requestAnimationFrame for animation because that's what it's for. Browsers can sync to the screen refresh to give you buttery smooth animation. They can also stop processing if your page is not visible. setTimeout on the other hand is not designed for animation, will not be synchronised to the browser's page drawing.

You should probably not use Date.now() for computing FPS as Date.now() only returns milliseconds. Also using (new Date()).getTime() is especially bad since it's generating a new Date object every frame.

requestAnimationFrame already gets passed the time in microseconds since the page loaded so just use that.

It's also common to average the FPS across frames.

const fpsElem = document.querySelector("#fps");
const avgElem = document.querySelector("#avg");

const frameTimes = [];
let   frameCursor = 0;
let   numFrames = 0;   
const maxFrames = 20;
let   totalFPS = 0;

let then = 0;
function render(now) {
  now *= 0.001;                          // convert to seconds
  const deltaTime = now - then;          // compute time since last frame
  then = now;                            // remember time for next frame
  const fps = 1 / deltaTime;             // compute frames per second
  
  fpsElem.textContent = fps.toFixed(1);  // update fps display
  
  // add the current fps and remove the oldest fps
  totalFPS += fps - (frameTimes[frameCursor] || 0);
  
  // record the newest fps
  frameTimes[frameCursor++] = fps;
  
  // needed so the first N frames, before we have maxFrames, is correct.
  numFrames = Math.max(numFrames, frameCursor);
  
  // wrap the cursor
  frameCursor %= maxFrames;
    
  const averageFPS = totalFPS / numFrames;

  avgElem.textContent = averageFPS.toFixed(1);  // update avg display
  
  requestAnimationFrame(render);
}
requestAnimationFrame(render);

body { font-family: monospace; }

<div>        fps: <span id="fps"></span></div>
<div>average fps: <span id="avg"></span></div>

I assume you are calling drawScene repeatedly but if you are setting x only once then it will not update every time drawScene is called. Also what you are storing in Time is elapsed time and not frames per second.

How about something like the below? The idea is to count the number of frames rendered and once one second has passed store that in the fps variable.

<script>
var elapsedTime = 0;
var frameCount = 0;
var lastTime = 0;

function drawScene() {

   // draw scene here

   var now = new Date().getTime();

   frameCount++;
   elapsedTime += (now - lastTime);

   lastTime = now;

   if(elapsedTime >= 1000) {
       fps = frameCount;
       frameCount = 0;
       elapsedTime -= 1000;

       document.getElementById('test').innerHTML = fps;
   }
}

lastTime = new Date().getTime();
setInterval(drawScene,33);

</script>

<div id="test">
</div>

I created an object oriented version of Barış Uşaklı's answer. It also tracks the average fps over the last minute.

Usage:

global Variable:

var fpsCounter;

Create the object somewhere when starting your program:

 fpsCounter = new FpsCounter();

Call the update method in your draw() funktion & update the fps-displays:

function drawScene() {          
  fpsCounter.update();
  document.getElementById('fpsDisplay').innerHTML = fpsCounter.getCountPerSecond();
  document.getElementById('fpsMinuteDisplay').innerHTML = fpsCounter.getCountPerMinute();
  // Code   
}

Note: I only put the fps-display updates in the draw function for simplicity. With 60fps it gets set 60 times per second, even though once a second is enough.

FpsCounter Code:

function FpsCounter(){
    this.count = 0;
    this.fps = 0;
    this.prevSecond;  
    this.minuteBuffer = new OverrideRingBuffer(60);
}

FpsCounter.prototype.update = function(){
    if (!this.prevSecond) {     
        this.prevSecond = new Date().getTime();
            this.count = 1;
    }
    else {
        var currentTime = new Date().getTime();
        var difference = currentTime - this.prevSecond;
        if (difference > 1000) {      
            this.prevSecond = currentTime;
            this.fps = this.count; 
            this.minuteBuffer.push(this.count);
            this.count = 0;
        }
        else{
            this.count++;
        }
    }    
};

FpsCounter.prototype.getCountPerMinute = function(){
    return this.minuteBuffer.getAverage();
};

FpsCounter.prototype.getCountPerSecond = function(){
    return this.fps;
};

OverrideBuffer Code:

function OverrideRingBuffer(size){
    this.size = size;
    this.head = 0;
    this.buffer = new Array();
};

OverrideRingBuffer.prototype.push = function(value){      
    if(this.head >= this.size) this.head -= this.size;    
    this.buffer[this.head] = value;
    this.head++;
};

OverrideRingBuffer.prototype.getAverage = function(){
    if(this.buffer.length === 0) return 0;

    var sum = 0;    

    for(var i = 0; i < this.buffer.length; i++){
        sum += this.buffer[i];
    }    

    return (sum / this.buffer.length).toFixed(1);
};

Since none of the other answers addressed the "in WebGL" part of the question, I'll add the following important details when measuring FPS in WebGL correctly.

window.console.time('custom-timer-id');    // start timer

/* webgl draw call here */                 // e.g., gl.drawElements();

gl.finish();                               // ensure the GPU is ready

window.console.timeEnd('custom-timer-id'); // end timer

For simplicity I used the console timer. I'm trying to make the point to always use WebGLRenderingContext.finish() to ensure the correct time is measured as all WebGL calls to the GPU are asynchronous!

Using a rotating array can do better. with dom element:

<div id="fps">

the following script do the trick:

var fpsLastTick = new Date().getTime();
var fpsTri = [15, 15, 15]; // aims for 60fps

function animate() {
  // your rendering logic blahh blahh.....


  // update fps at last
  var now = new Date().getTime();
  var frameTime = (now - fpsLastTick);
  fpsTri.shift(); // drop one
  fpsTri.push(frameTime); // append one
  fpsLastTick = now;
  fps = Math.floor(3000 / (fpsTri[0] + fpsTri[1] + fpsTri[2])); // mean of 3
  var fpsElement = document.getElementById('fps')
  if (fpsElement) {
    fpsElement.innerHTML = fps;
  }
}

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