Refactoring: float4 -> float3 where it makes sense.
Refactor: idiomize and declutter
Refactor: more idioms.
Refactor: More idioms.  Minor numerical change...

Convert x / dot(x,x) to normalize(x), which is "better", but changes behaviour
slightly.
Refactor: break interpolation into its own function.
Refactor: cleanup variables as much as I can.
Refactor: polar to cartesian in function.
Refactor: comment changes and move no-path