I was not expecting to be able to reach that point so easily, but pretty much every feature took somewhere between 30 minutes and 1 hour - 1 to 3 prompts on average. It is vibe-coded in the sense that I haven't looked at the code, but I am very careful with my prompts and constantly have Claude reviewing the codebase, looking for performance and code quality improvements.
It can reach 2000 draw calls on recent integrated GPUs, such as modern phones or MacBooks, where Three.js usually starts dropping frames at 300-600 draw calls. I love Three.js, but I wanted to build something more minimal that does exactly what I need with better performance.
I started with a C/WASM core but ended up sticking with JS because the performance difference wasn't significant enough for the number of entities in my game (never more than 500 entities).
All in all, it was a fascinating experience, and I learned a lot about engines, even without typing a single line of code. It's pretty wild that we can now quite easily build in-house engines alongside our games as solo developers.