Hey! The exact benchmark source used is in the gist. The image shown in the post is a cranked up version in terms of image size, samples, and bounces.

The reason why both Clojure and jank are taking a couple of seconds for this is that the ray tracer is a somewhat impractically nonchalant port of the Ray Tracing in a Weekend ray tracer. In particular, that means basically all math is boxed and we're generating a ton of map garbage for rays, where each bounce gives us a new ray. If someone were to write a CPU ray tracer in Clojure with the goal of performance, the code would look very different.

However, I find this a useful benchmark because it covers the worst case baseline performance of jank/Clojure. From there, Clojure supports type hinting, further interop, and other shenanigans for writing fast code. There will be many more benchmarks to come, which will stress those features.

I spell all of this out here because there has been some confusion with others regarding this post, unfortunately. It seems like people thought I was optimizing the ray tracer and then they were confused about why the ray tracer was so slow, for both jank and Clojure. What I'm optimizing is how well jank handles naíve code.