LineRenderer on Mesh surface

Question

Goal: Render distance lines between two points on the surface of a mesh-based primitive (i.e. sphere, cube, etc).

Current Solution: Iteratively traverse distance line between two end points and "reverse" raycast through this point somehow. Since the distance line directly connects both vertices through the mesh, the according points on the mesh surface are required.

Ray ray = new Ray();
RaycastHit raycastHit;
ray.origin = posOnDistanceLine;
ray.direction = raycastNormal.normalized;
// Reverse ray since we can't raycast from inside the mesh
ray.origin = ray.GetPoint(1);
ray.direction = -ray.direction;

Lines are then drawn using Unity's LineRenderer which is being populated with positions of vertices whenever a change in normals (to previous raycast) is identified.

Issues:

• Horrible performance (as 100 rays are cast whenever the end points move).

• Solution doesn't always work and produces unexpected, jagged lines / points.

Question: Is there a better approach to implement this?

Answer 1

This is effectively a navmesh pathing problem.

First, you'll iterate over your mesh data (vertex positions and triangle indices) and build a set of adjacency information - so you can associate each triangle with its adjacent edges, and from there to its neighbouring triangles. I describe a version of this process in another answer.

Next, you can use a pathfinding algorithm like A* to determine a path across the adjacency graph you've created, joining your initial triangle to your destination triangle. You can use a funnel algorithm to pull this path "taut," finding the crossing point along each edge that minimizes the length of the resulting path.

Lastly, you can walk over each segment of the resulting path, adding a point to your line renderer wherever it crosses a triangle edge, and summing the length of the segments you've built to determine the total measurement.