The basic idea for the anti-aliasing is to take many samples inside every pixel and average them out which smooths outs the edges. The problem with the lights, as the other commenter explained, is that even with this the light is so bright that there is still a hard edge between the adjoining pixels.
The 3rd book [0] is primarily about implementing an MC ray tracer and then adding the techniques in the second paper you linked. That's what I've used in my code as well. I just skimmed through the paper and I think the book covers most of the material from the paper with the exception of spatial subdivision. I will have a more careful read later to see exactly what my implementation is missing from this.
Do you happen to have a link to any reference material or paper explaining the technique you are describing or a term for it I can search for? I knew why this aliasing was happening, but I wasn't quite sure how to fix it.
This is my first attempt at graphics programming and as I went through it I was quite surprised by the simplicity of ray tracing. Before this, I hadn't imagined you could get beautiful pictures with so little code. I found the whole thing quite elegant.
Hey. At the moment what is implemented is exactly what you are going to find in the three books of the Ray Tracing in a Weekend series. If I can find the time to continue this project, I am going to make a git tag for the current version for people who just want to use this while going through the books and I will also add a changelog for any changes I make from that point onward.
I started this project last year when I was looking for something fun to learn Rust with and I had Peter Shirley's excellent Ray Tracing in a Weekend series of books recommended to me. In the process I got interested in learning ray-tracing for its own sake so I decided to finish all three books and I am now considering continuing this further on my own.
I am sharing in case this is useful to others who are on a similar path to where I was.
[0] https://raytracing.github.io/books/RayTracingInOneWeekend.ht...