SkinnedMesh: Update "applyBoneTransform" to optionally take Vector4, support direction or position transformation (mrdoob#33091)

Author: gkjohnson

src/objects/SkinnedMesh.js

@@ -8,12 +8,12 @@ import { Ray } from '../math/Ray.js';
 import { AttachedBindMode, DetachedBindMode } from '../constants.js';
 import { warn } from '../utils.js';
 
-const _basePosition = /*@__PURE__*/ new Vector3();
+const _baseVector = /*@__PURE__*/ new Vector4();
 
 const _skinIndex = /*@__PURE__*/ new Vector4();
 const _skinWeight = /*@__PURE__*/ new Vector4();
 
-const _vector3 = /*@__PURE__*/ new Vector3();
+const _vector4 = /*@__PURE__*/ new Vector4();
 const _matrix4 = /*@__PURE__*/ new Matrix4();
 const _vertex = /*@__PURE__*/ new Vector3();
 
@@ -309,12 +309,12 @@ class SkinnedMesh extends Mesh {
 
 	/**
 	 * Applies the bone transform associated with the given index to the given
-	 * vertex position. Returns the updated vector.
+	 * vector. Can be used to transform positions or direction vectors by providing
+	 * a Vector4 with 1 or 0 in the w component respectively. Returns the updated vector.
 	 *
 	 * @param {number} index - The vertex index.
-	 * @param {Vector3} target - The target object that is used to store the method's result.
-	 * the skinned mesh's world matrix will be used instead.
-	 * @return {Vector3} The updated vertex position.
+	 * @param {Vector3|Vector4} target - The target object that is used to store the method's result.
+	 * @return {Vector3|Vector4} The updated vertex attribute data.
 	 */
 	applyBoneTransform( index, target ) {
 
@@ -324,9 +324,19 @@ class SkinnedMesh extends Mesh {
 		_skinIndex.fromBufferAttribute( geometry.attributes.skinIndex, index );
 		_skinWeight.fromBufferAttribute( geometry.attributes.skinWeight, index );
 
-		_basePosition.copy( target ).applyMatrix4( this.bindMatrix );
+		if ( target.isVector4 ) {
+
+			_baseVector.copy( target );
+			target.set( 0, 0, 0, 0 );
+
+		} else {
+
+			_baseVector.set( ...target, 1 );
+			target.set( 0, 0, 0 );
 
-		target.set( 0, 0, 0 );
+		}
+
+		_baseVector.applyMatrix4( this.bindMatrix );
 
 		for ( let i = 0; i < 4; i ++ ) {
 
@@ -338,12 +348,19 @@ class SkinnedMesh extends Mesh {
 
 				_matrix4.multiplyMatrices( skeleton.bones[ boneIndex ].matrixWorld, skeleton.boneInverses[ boneIndex ] );
 
-				target.addScaledVector( _vector3.copy( _basePosition ).applyMatrix4( _matrix4 ), weight );
+				target.addScaledVector( _vector4.copy( _baseVector ).applyMatrix4( _matrix4 ), weight );
 
 			}
 
 		}
 
+		if ( target.isVector4 ) {
+
+			// ensure the homogenous coordinate remains unchanged after vector operations
+			target.w = _baseVector.w;
+
+		}
+
 		return target.applyMatrix4( this.bindMatrixInverse );
 
 	}