[unholiness]

I cringed very hard in the slerp example seeing `acos(dot(a,b))`. Clamping to [-1,1] to avoid NaNs still gives you bad answers and numerical sensitivity around small angles. acos and asin in general lose ~half your sig figs around their singularities[0]. Working around this by introducing a threshold seems like exactly same flavor of issue he's complaining about to begin with.

There are perfectly good solutions for finding the angle using atan and the cross product. Calculating A x B will yield a vector which lies is along their normal with length tan(θ)(A · B) so we can straightforwardly say e.g.:

`θ = atan2(norm(A ⅹ B), (A · B))`

No thresholds, no branching, only ~1 bit of significance lost. As the original author says himself, when you're introducing arbitrary-feeling thresholds, it's likely you're missing a solution which would improve more than just the weirdness at those thresholds.

[0] A good analysis of this is on Page 46 here, including a more optimized (but less obviously true) alternative to the formula above: https://people.eecs.berkeley.edu/~wkahan/Mindless.pdf