Updated builds.

build/three.js

@@ -35444,9 +35444,6 @@
 
 		this.setInterpolation( interpolation || this.DefaultInterpolation );
 
-		this.validate();
-		this.optimize();
-
 	}
 
 	// Static methods
@@ -35571,12 +35568,14 @@
 				}
 
 				console.warn( 'THREE.KeyframeTrack:', message );
-				return;
+				return this;
 
 			}
 
 			this.createInterpolant = factoryMethod;
 
+			return this;
+
 		},
 
 		getInterpolation: function () {
@@ -36113,8 +36112,6 @@
 
 		}
 
-		this.optimize();
-
 	}
 
 	function getTrackTypeForValueTypeName( typeName ) {
@@ -36489,6 +36486,8 @@
 
 			this.duration = duration;
 
+			return this;
+
 		},
 
 		trim: function () {
@@ -36503,6 +36502,20 @@
 
 		},
 
+		validate: function () {
+
+			var valid = true;
+
+			for ( var i = 0; i < this.tracks.length; i ++ ) {
+
+				valid = valid && this.tracks[ i ].validate();
+
+			}
+
+			return valid;
+
+		},
+
 		optimize: function () {
 
 			for ( var i = 0; i < this.tracks.length; i ++ ) {
@@ -41843,13 +41856,19 @@
 		_updateTime: function ( deltaTime ) {
 
 			var time = this.time + deltaTime;
+			var duration = this._clip.duration;
+			var loop = this.loop;
+			var loopCount = this._loopCount;
+
+			var pingPong = ( loop === LoopPingPong );
 
-			if ( deltaTime === 0 ) return time;
+			if ( deltaTime === 0 ) {
 
-			var duration = this._clip.duration,
+				if ( loopCount === - 1 ) return time;
 
-				loop = this.loop,
-				loopCount = this._loopCount;
+				return ( pingPong && ( loopCount & 1 ) === 1 ) ? duration - time : time;
+
+			}
 
 			if ( loop === LoopOnce ) {
 
@@ -41886,8 +41905,6 @@
 
 			} else { // repetitive Repeat or PingPong
 
-				var pingPong = ( loop === LoopPingPong );
-
 				if ( loopCount === - 1 ) {
 
 					// just started

build/three.module.js

@@ -35438,9 +35438,6 @@ function KeyframeTrack( name, times, values, interpolation ) {
 
 	this.setInterpolation( interpolation || this.DefaultInterpolation );
 
-	this.validate();
-	this.optimize();
-
 }
 
 // Static methods
@@ -35565,12 +35562,14 @@ Object.assign( KeyframeTrack.prototype, {
 			}
 
 			console.warn( 'THREE.KeyframeTrack:', message );
-			return;
+			return this;
 
 		}
 
 		this.createInterpolant = factoryMethod;
 
+		return this;
+
 	},
 
 	getInterpolation: function () {
@@ -36107,8 +36106,6 @@ function AnimationClip( name, duration, tracks ) {
 
 	}
 
-	this.optimize();
-
 }
 
 function getTrackTypeForValueTypeName( typeName ) {
@@ -36483,6 +36480,8 @@ Object.assign( AnimationClip.prototype, {
 
 		this.duration = duration;
 
+		return this;
+
 	},
 
 	trim: function () {
@@ -36497,6 +36496,20 @@ Object.assign( AnimationClip.prototype, {
 
 	},
 
+	validate: function () {
+
+		var valid = true;
+
+		for ( var i = 0; i < this.tracks.length; i ++ ) {
+
+			valid = valid && this.tracks[ i ].validate();
+
+		}
+
+		return valid;
+
+	},
+
 	optimize: function () {
 
 		for ( var i = 0; i < this.tracks.length; i ++ ) {
@@ -41837,13 +41850,19 @@ Object.assign( AnimationAction.prototype, {
 	_updateTime: function ( deltaTime ) {
 
 		var time = this.time + deltaTime;
+		var duration = this._clip.duration;
+		var loop = this.loop;
+		var loopCount = this._loopCount;
+
+		var pingPong = ( loop === LoopPingPong );
 
-		if ( deltaTime === 0 ) return time;
+		if ( deltaTime === 0 ) {
 
-		var duration = this._clip.duration,
+			if ( loopCount === - 1 ) return time;
 
-			loop = this.loop,
-			loopCount = this._loopCount;
+			return ( pingPong && ( loopCount & 1 ) === 1 ) ? duration - time : time;
+
+		}
 
 		if ( loop === LoopOnce ) {
 
@@ -41880,8 +41899,6 @@ Object.assign( AnimationAction.prototype, {
 
 		} else { // repetitive Repeat or PingPong
 
-			var pingPong = ( loop === LoopPingPong );
-
 			if ( loopCount === - 1 ) {
 
 				// just started