Maybe you can take something from there.
https://github.com/hofk/THREEf.js/blob/7b76151f112779f48f16878c571541d44b00a70b/THREEf_90/THREEf.js
lines 36, 108, 311, 600, 1332, 2349, 2370, 2394, 2517, 2584, 2610, 2954, 2985, 3017
Try it out there https://hofk.de/main/threejs/sandboxthreef/
