Segment types
Concave Up
A valley. Extra vertices along the dip so the mesh holds its shape.
Concave Down
A hill. A triangle fan from a center point under the peak.
Bridge
A flat span. A simple strip between the two edges.
How it was built
Unity (C#). PathEditor puts position handles on every node. RemeshedPath has Remesh and Clear. PathRenderer builds the mesh from the three segment types. Drop-in prefabs: Path, Node, Remeshed Path, and Path Renderer.
The hard parts
The mesh has to stay cheap while nodes move. Each span picks a segment type so the triangulation does not explode — a valley fans from the bottom, a hill from a center, a bridge stays a strip.