three.js/src/objects/Bone.js

/**
 * @author mikael emtinger / http://gomo.se/
 * @author alteredq / http://alteredqualia.com/
 */

THREE.Bone = function( belongsToSkin ) {

	THREE.Object3D.call( this );

	this.skin = belongsToSkin;
	this.skinMatrix = new THREE.Matrix4();

};

THREE.Bone.prototype = Object.create( THREE.Object3D.prototype );

THREE.Bone.prototype.update = function ( parentSkinMatrix, forceUpdate ) {

	// update local

	if ( this.matrixAutoUpdate ) {

		forceUpdate |= this.updateMatrix();

	}

	// update skin matrix

	if ( forceUpdate || this.matrixWorldNeedsUpdate ) {

		if( parentSkinMatrix ) {

			this.skinMatrix.multiplyMatrices( parentSkinMatrix, this.matrix );

		} else {

			this.skinMatrix.copy( this.matrix );

		}

		this.matrixWorldNeedsUpdate = false;
		forceUpdate = true;

	}

	// update children

	var child, i, l = this.children.length;

	for ( i = 0; i < l; i ++ ) {

		this.children[ i ].update( this.skinMatrix, forceUpdate );

	}

};