javascript - Recording FPS in webGL

Question

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!

Answer 1

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>