VEX code for getting an in-order traversal of the neighbours of a point; assumes connected primitives.

inorder-neighbour-traversal.cpp

/* returns the in-order neighbours of a point - based on matching primitives */
void inorder_neighbours(int point_number; int points[] /* returned */) {
    int nc = neighbourcount(geoself(), point_number);
    resize(points, nc);

    int prims[] = pointprims(geoself(), point_number);
    
    int points_in_prim[] = primpoints(geoself(), prims[0]);
    //
    // WE EXPECT THREE POINTS PER PRIMITIVE!!!
    //
    int j = 0;
    for (int i = 0; i < 3; ++i) {
        if (points_in_prim[i] != point_number) {
                        // the first primitive determines our traversal order
                points[j++] = points_in_prim[i];
        }
    }
    for (int i = 2; i < nc; ++i) {
        // we already used up one primitive
        int found = 0;
        for (j = i - 1; j < len(prims); ++j) {
                points_in_prim = primpoints(geoself(), prims[j]);
                int candidate_point = -1;
                int candidate_prim_idx = -1;
                foreach(int pt; points_in_prim) {
                        if (pt != point_number) {
                            if (pt == points[i-1]) {
                                found = 1;
                            } else {
                                candidate_point = pt;
                                candidate_prim_idx = j;
                            }
                        }
                }
                if (found) {
                        points[i] = candidate_point;
                        // each time we find a primitive we have to use it up.
                        if (candidate_prim_idx != i - 1) {
                            prims[candidate_prim_idx] = prims[i-1];
                        }
                        break;
                }
        }
        assert(found);
    }
}