SkeletonHelper is not rendered - three.js

Question

I am trying to display a Three JS Skeleton using SkeletonHelper.
According to this answer, SkeletonHelper() takes the root bone. I have done just that. But it is not being displayed. Why is this the case?
var bones = []
var shoulder = new THREE.Bone();
var elbow = new THREE.Bone();
var hand = new THREE.Bone();
shoulder.add(elbow);
elbow.add(hand);
bones.push(shoulder);
bones.push(elbow);
bones.push(hand);
skeleton = new THREE.Skeleton(bones)
skeleton_helper = new THREE.SkeletonHelper(shoulder)
scene.add(skeleton_helper)
}
Thanks for the help!

Answer 1

THREE.SkeletonHelper assumes that the world matrices of the bones are up-to-date. So by adding a transformation to your bones and then adding the top-most bone to the scene, you should see your desired result. That works because the renderer ensures correct world matrices of the entire scene graph.
var bones = [];
var shoulder = new THREE.Bone();
var elbow = new THREE.Bone();
var hand = new THREE.Bone();
shoulder.add( elbow );
elbow.add( hand );
bones.push( shoulder );
bones.push( elbow );
bones.push( hand );
shoulder.position.y = 0;
elbow.position.y = - 1;
hand.position.y = - 0.5;
var armSkeleton = new THREE.Skeleton( bones );
var skeleton_helper = new THREE.SkeletonHelper( shoulder );
scene.add( skeleton_helper );
scene.add( shoulder );
https://jsfiddle.net/xvbLwyaq/3/
three.js R103