It’s now been just over three months since Wenzel, Greg, and I put Physically Based Rendering online. I’m happy to say that I can now start to relax as I’ve started to become comfortable that we don’t seem to have made any horribly embarrassing errors in the conversion to the online edition. I’m even getting over having seen it described a few times as a “free online ebook,” a phrase that has never exactly sounded like a hallmark of high quality to me.

We don’t use any tracking scripts and aren’t logging page requests, so we have little insight into how many people are making use of the online edition, which sections are getting the most attention, and so forth. Occasionally, I wish we knew a little more about that, but I also like the idea of trying to do something well and then putting it out there without worrying about trying to measure how it’s being received. Sort of a little strike against the dopamine of likes, retweets, and engagement-driven metrics (oh hai, PMs!), if you will.

There are two measures we do have available, however, so we’re not fully dopamine-free around here. They are the amount of bandwidth used to serve the website and the total number of http requests. (It so happens that those are also the two things that Google charges us for.) From those, we can see that we passed the terabyte milestone a few weeks ago, and as of January 21, 2019, just over 1.3 TB of data has been served for pbr-book.org, over a total of 2.6 million individual http requests.

After a first spike at launch, it’s been a fairly consistent 9 GB or so of bandwidth per day since then. 6% of it has been to China and 18% to the rest of APAC. For the other 76%, we don’t have any further insight other than Australia doing its part at 1.25%.

A full read-through of the online version of book consumes about 300 MB of bandwidth, so we’re serving it up at a pace of corresponds to about 4,500 full readings of the book in 3 months. (I assume, however, that more of the accesses are from people looking up specific topics.) Although some of that bandwidth is presumably web crawlers, the total is much more than I’d have expected, which is a nice reward for the work it took to prepare the online edition.

The total serving costs so far add up to about $175, so the free version is sustainable, especially with the help of everyone who is supporting the online edition on patreon—that more than covers the hosting costs—thanks, patreon supporters!

With the online third edition of the book in good shape, we’ve started work on an updated edition of Physically Based Rendering for 2019. It will have roughly half as much updated as has been between the previous printed editions of the book, but I think we’ve got a healthy bunch of improvements in the queue, including full-spectral rendering, many improvements to samplers and sampling routines, a many-light sampling implementation, and various reductions in memory use. We’re very much looking forward to getting that update out and available to everyone (though there’s a lot of work to do, and it will certainly be late in the year!)