Add display-frame-rate.js script

resources/display-frame-rate.js

@@ -0,0 +1,35 @@
+/**
+ * Display frame rate in a span element added to the navigation bar.
+ */
+(function() {
+
+  var container = document.querySelector('.navbar .navbar-inner .container');
+  if (!container) {
+    return;
+  }
+
+  var fpsElement = document.createElement('span');
+  fpsElement.style.color = 'white';
+
+  container.appendChild(fpsElement);
+
+  var frameCount = 0;
+  var begin = +new Date();
+
+  window.setInterval(function() {
+    var end = +new Date();
+    var milliseconds = end - begin;
+    var seconds = milliseconds / 1000.0;
+    var frameRate = frameCount / seconds;
+    fpsElement.innerHTML = frameRate.toPrecision(4) + ' fps';
+    frameCount = 0;
+    begin = end;
+  }, 500);
+
+  var go = function() {
+    frameCount++;
+    window.requestAnimationFrame(go);
+  };
+  go();
+
+})();