Transplanted @WestLangley's normal matrix fix from Geometry.applyMatrix to BufferGeometry.

See #2610

build/three.js

@@ -1565,6 +1565,28 @@ THREE.Matrix3.prototype = {
 
 	},
 
+	multiplyVector3Array: function ( a ) {
+
+		var tmp = THREE.Matrix3.__v1;
+
+		for ( var i = 0, il = a.length; i < il; i += 3 ) {
+
+			tmp.x = a[ i ];
+			tmp.y = a[ i + 1 ];
+			tmp.z = a[ i + 2 ];
+
+			this.multiplyVector3( tmp );
+
+			a[ i ]     = tmp.x;
+			a[ i + 1 ] = tmp.y;
+			a[ i + 2 ] = tmp.z;
+
+		}
+
+		return a;
+
+	},
+
 	getInverse: function ( matrix ) {
 
 		// input: THREE.Matrix4
@@ -1637,7 +1659,8 @@ THREE.Matrix3.prototype = {
 	}
 
 };
-/**
+
+THREE.Matrix3.__v1 = new THREE.Vector3();/**
  * @author mrdoob / http://mrdoob.com/
  * @author supereggbert / http://www.paulbrunt.co.uk/
  * @author philogb / http://blog.thejit.org/
@@ -5714,10 +5737,13 @@ THREE.BufferGeometry.prototype = {
 
 		if ( normalArray !== undefined ) {
 
-			var matrixRotation = new THREE.Matrix4();
-			matrixRotation.extractRotation( matrix );
+			var normalMatrix = new THREE.Matrix3();
+			normalMatrix.getInverse( matrix ).transpose();
+
+			normalMatrix.multiplyVector3Array( normalArray );
+
+			this.normalizeNormals();
 
-			matrixRotation.multiplyVector3Array( normalArray );
 			this.normalsNeedUpdate = true;
 
 		}
@@ -5916,15 +5942,27 @@ THREE.BufferGeometry.prototype = {
 
 			}
 
-			// normalize normals
+			this.normalizeNormals();
+
+			this.normalsNeedUpdate = true;
+
+		}
+
+	},
+
+	normalizeNormals: function () {
+
+		var normals = this.attributes[ "normal" ].array;
+
+		var x, y, z, n;
 
-			for ( i = 0, il = normals.length; i < il; i += 3 ) {
+		for ( var i = 0, il = normals.length; i < il; i += 3 ) {
 
 			x = normals[ i ];
 			y = normals[ i + 1 ];
 			z = normals[ i + 2 ];
 
-				var n = 1.0 / Math.sqrt( x * x + y * y + z * z );
+			n = 1.0 / Math.sqrt( x * x + y * y + z * z );
 
 			normals[ i ] 	 *= n;
 			normals[ i + 1 ] *= n;
@@ -5932,10 +5970,6 @@ THREE.BufferGeometry.prototype = {
 
 		}
 
-			this.normalsNeedUpdate = true;
-
-		}
-
 	},
 
 	computeTangents: function () {

src/core/BufferGeometry.js

@@ -50,10 +50,13 @@ THREE.BufferGeometry.prototype = {
 
 		if ( normalArray !== undefined ) {
 
-			var matrixRotation = new THREE.Matrix4();
-			matrixRotation.extractRotation( matrix );
+			var normalMatrix = new THREE.Matrix3();
+			normalMatrix.getInverse( matrix ).transpose();
+
+			normalMatrix.multiplyVector3Array( normalArray );
+
+			this.normalizeNormals();
 
-			matrixRotation.multiplyVector3Array( normalArray );
 			this.normalsNeedUpdate = true;
 
 		}
@@ -252,15 +255,27 @@ THREE.BufferGeometry.prototype = {
 
 			}
 
-			// normalize normals
+			this.normalizeNormals();
+
+			this.normalsNeedUpdate = true;
+
+		}
+
+	},
+
+	normalizeNormals: function () {
+
+		var normals = this.attributes[ "normal" ].array;
+
+		var x, y, z, n;
 
-			for ( i = 0, il = normals.length; i < il; i += 3 ) {
+		for ( var i = 0, il = normals.length; i < il; i += 3 ) {
 
 			x = normals[ i ];
 			y = normals[ i + 1 ];
 			z = normals[ i + 2 ];
 
-				var n = 1.0 / Math.sqrt( x * x + y * y + z * z );
+			n = 1.0 / Math.sqrt( x * x + y * y + z * z );
 
 			normals[ i ] 	 *= n;
 			normals[ i + 1 ] *= n;
@@ -268,10 +283,6 @@ THREE.BufferGeometry.prototype = {
 
 		}
 
-			this.normalsNeedUpdate = true;
-
-		}
-
 	},
 
 	computeTangents: function () {

src/core/Matrix3.js

@@ -27,6 +27,28 @@ THREE.Matrix3.prototype = {
 
 	},
 
+	multiplyVector3Array: function ( a ) {
+
+		var tmp = THREE.Matrix3.__v1;
+
+		for ( var i = 0, il = a.length; i < il; i += 3 ) {
+
+			tmp.x = a[ i ];
+			tmp.y = a[ i + 1 ];
+			tmp.z = a[ i + 2 ];
+
+			this.multiplyVector3( tmp );
+
+			a[ i ]     = tmp.x;
+			a[ i + 1 ] = tmp.y;
+			a[ i + 2 ] = tmp.z;
+
+		}
+
+		return a;
+
+	},
+
 	getInverse: function ( matrix ) {
 
 		// input: THREE.Matrix4
@@ -99,3 +121,5 @@ THREE.Matrix3.prototype = {
 	}
 
 };
+
+THREE.Matrix3.__v1 = new THREE.Vector3();
\ No newline at end of file