RiverModeler.onPreRebuildRiver += OnRiverRebuild;
RiverModeler.onPostRebuildRiver += OnRiverRebuild;

Sampling the river surface

Generally, you can sample the same spline used by a river to get its position/direction/normal using Spline.Evalutate(t);. But the River Modeler component contains a helper function that simplifies this:

RiverModeler.FindNearestPointOnRiver(float3 worldPosition, out float3 point, out float3 direction, out float3 normal, out float t, float sampleDistance = 1f);

This is excellent to use for controlling particle effects, swimming behaviour or buoyancy physics!

Procedural Splines

If you’re looking to generate a spline from a set of points, that is certainly possible. Unity’s Splines API contains this function which can be used for it:

FitSplineToPoints(List<float3> positions, float errorThreshold, bool closed, out Spline spline);

If you have the Spline Extensions asset installed, you can use a multithreaded variant that’s x26 times faster

CreateSplineFromPoints.Execute(List<float3> positions, float errorThreshold, bool closed, out Spline spline, float3 up = default);