random points on meshes

RandomThings.cs

public class RandomThings {
  public void CalculateRandomPointsOnMeshes(MeshFilter[] meshFilters, Vector3[] dst, Vector3? direction) {
        //find all the meshes

        float weight = 0;
        foreach (var filter in meshFilters) {
            var mesh = filter.sharedMesh;
            var vs = mesh.vertices;
            for(int i = 0; i < vs.Length; ++i) {
                vs[i] = filter.transform.TransformPoint(vs[i]);
            }
            var tris = mesh.triangles;

            for(int i = 0; i < tris.Length/3; ++i) {
                var a = vs[tris[i * 3 + 0]];
                var b = vs[tris[i * 3 + 1]];
                var c = vs[tris[i * 3 + 2]];

                Vector3 cross = Vector3.Cross(b - a, c - a);
                var dir = direction ?? cross.normalized;
                float area = Vector3.Dot(dir, cross); //area of triangle projected onto xz plane. negative if it's facing away from dir
                if (area < 0) continue; //skip backward triangles
                weight += area;
                for(int j = 0; j < dst.Length; ++j) {
                    var r = Random.Range(0, weight);
                    if(r< area) {
                        dst[j] = RandomPointInTriangle(a, b, c);
                    }
                }
            }
        }
        this.area = weight;
    }

    public Vector3 RandomPointInTriangle(Vector3 a, Vector3 b, Vector3 c) {
        float br = Random.value;
        float cr = Random.value;
        //if outside triangle, map it back in
        if(br+cr > 1) {
            br = 1 - br;
            cr = 1 - cr;
        }
        float ar = 1 - br - cr;
        return a * ar + b * br + c * cr;
    }
  }