Right, it's a spectrum, you can't avoid some things (and rightly so).

Another soft rule: no member functions (except for the Scenes); structs are only data, all functions are free functions.

Also no operator overloading, so yes, lots of Vec3::add(&v1, &v2). I was hesitant at first but this makes for more transparent ops (* is dot or cross?) and does not hide the complexity.

The whole thing is around 6-7kloc and I think it would be possible to rewrite in C++ in a day or two.

I don't find the idea of rewriting the subset of a blas library I want to use for each project very fun, but I bet with so few dependencies a stripped binary gets pretty small.