hmm, source code not visible...
As both of these solutions were developed on company time, there were limits as to how much code we could publish. All the same, I would have liked to have provided a demo for the HZB method, but just writing the chapter was enough extra work in addition to my day job!
You're in luck though, since Daniel Rákos and Nick Darnell have also written on the subject of HZB occlusion testing and both of them provide standalone demos. The course notes for the Froblins talk also has code, but they fail to account for distortion of the object's bounding sphere due to perspective projection (Nick's code does though).
I'll see if I can go into more details about exactly what we did there at a later date, but it's not really as interesting as the topic of occlusion testing itself.
Great article! The Conviction solution looks really smart and promising, wish I had time to give it a try.
Thanks! Expect to see more of this GPU-CPU interoperability in the future! :)