Added THREE.Timer. (#17912)

* Added THREE.Timer.

* Timer: Make now() private.

* Timer: Fix typo.

* Timer: Shorten method and variable names.

* Timer: Remove js and add d.ts file.

* Timer: Transform to class.

* Update webgl_morphtargets_sphere.html

* Delete Timer.d.ts

* Update webgl_morphtargets_sphere.html

* Timer: Add optional timestamp parameter to update().

* Timer: Fix multiple instance usage.

* Timer: Clean up.

examples/jsm/misc/Timer.js

@@ -0,0 +1,144 @@
+class Timer {
+
+	constructor() {
+
+		this._previousTime = 0;
+		this._currentTime = 0;
+		this._startTime = now();
+
+		this._delta = 0;
+		this._elapsed = 0;
+
+		this._timescale = 1;
+
+		this._useFixedDelta = false;
+		this._fixedDelta = 16.67; // ms, corresponds to approx. 60 FPS
+
+		// use Page Visibility API to avoid large time delta values
+
+		this._usePageVisibilityAPI = ( typeof document !== 'undefined' && document.hidden !== undefined );
+
+		if ( this._usePageVisibilityAPI === true ) {
+
+			this._pageVisibilityHandler = handleVisibilityChange.bind( this );
+
+			document.addEventListener( 'visibilitychange', this._pageVisibilityHandler, false );
+
+		}
+
+	}
+
+	disableFixedDelta() {
+
+		this._useFixedDelta = false;
+
+		return this;
+
+	}
+
+	dispose() {
+
+		if ( this._usePageVisibilityAPI === true ) {
+
+			document.removeEventListener( 'visibilitychange', this._pageVisibilityHandler );
+
+		}
+
+		return this;
+
+	}
+
+	enableFixedDelta() {
+
+		this._useFixedDelta = true;
+
+		return this;
+
+	}
+
+	getDelta() {
+
+		return this._delta / 1000;
+
+	}
+
+	getElapsed() {
+
+		return this._elapsed / 1000;
+
+	}
+
+	getFixedDelta() {
+
+		return this._fixedDelta / 1000;
+
+	}
+
+	getTimescale() {
+
+		return this._timescale;
+
+	}
+
+	reset() {
+
+		this._currentTime = now() - this._startTime;
+
+		return this;
+
+	}
+
+	setFixedDelta( fixedDelta ) {
+
+		this._fixedDelta = fixedDelta * 1000;
+
+		return this;
+
+	}
+
+	setTimescale( timescale ) {
+
+		this._timescale = timescale;
+
+		return this;
+
+	}
+
+	update() {
+
+		if ( this._useFixedDelta === true ) {
+
+			this._delta = this._fixedDelta;
+
+		} else {
+
+			this._previousTime = this._currentTime;
+			this._currentTime = now() - this._startTime;
+
+			this._delta = this._currentTime - this._previousTime;
+
+		}
+
+		this._delta *= this._timescale;
+
+		this._elapsed += this._delta; // _elapsed is the accumulation of all previous deltas
+
+		return this;
+
+	}
+
+}
+
+function now() {
+
+	return ( typeof performance === 'undefined' ? Date : performance ).now();
+
+}
+
+function handleVisibilityChange() {
+
+	if ( document.hidden === false ) this.reset();
+
+}
+
+export { Timer };

examples/webgl_morphtargets_sphere.html

@@ -28,8 +28,9 @@
 
 			import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
 			import { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';
+			import { Timer } from 'three/addons/misc/Timer.js';
 
-			let camera, scene, renderer, clock;
+			let camera, scene, renderer, timer;
 
 			let mesh;
 
@@ -48,7 +49,7 @@
 
 				scene = new THREE.Scene();
 
-				clock = new THREE.Clock();
+				timer = new Timer();
 
 				const light1 = new THREE.PointLight( 0xff2200, 50000 );
 				light1.position.set( 100, 100, 100 );
@@ -102,8 +103,6 @@
 
 				window.addEventListener( 'resize', onWindowResize );
 
-				document.addEventListener( 'visibilitychange', onVisibilityChange );
-
 			}
 
 			function onWindowResize() {
@@ -115,30 +114,17 @@
 
 			}
 
-			function onVisibilityChange() {
-
-				if ( document.hidden === true ) {
-
-					clock.stop();
-
-				} else {
-
-					clock.start();
-
-				}
-
-			}
-
 			function animate() {
 
 				requestAnimationFrame( animate );
+				timer.update();
 				render();
 
 			}
 
 			function render() {
 
-				const delta = clock.getDelta();
+				const delta = timer.getDelta();
 
 				if ( mesh !== undefined ) {