How to get the face id?

[yihua7]

Thanks a lot for the excellent code!!! I'm asking if we could get the intersected face id from the code, which is really helpful in lots of cases.

[ashawkey]

The face id can be retrieved from here in the CUDA side, but it is not passed to the python side. You can add another buffer to output this value.

[yihua7]

I use a int64_t array face_idx to retrieve the p.first as this:

    // face normal is written to directions.
    if (p.first >= 0) {
        normals[i] = triangles[p.first].normal();
        face_idx[i] = p.first;
    } else {
        normals[i].setZero();
        face_idx[0] = -1;
    }

However, when I visualize the intersected face gathered by face_id, the results are inconsistent to the intersections. The latter is correct. The mesh model is from renderer.py. The yellow points are intersections and faces are picked by face_idx discussed above. The input rays_o and rays_d are:

    rays_o = torch.tensor([[0, 0, 0], [0, 0, 0], [0, 0, 0]]).float()
    rays_d = torch.tensor([[1, 0, 0], [0, 1, 0], [0, 0, 1]]).float()

Is there something wrong in my implementation? Thanks for your reply.

[yihua7]

The problem can be solved by adding an additional attribute to the structure Triangle : int64_t idx; Then initialize it here:

        for (size_t i = 0; i < n_triangles; i++) {
            triangles_cpu[i] = {vertices.row(triangles(i, 0)), vertices.row(triangles(i, 1)), vertices.row(triangles(i, 2)), (int64_t) i};
        }

And the buffer is set as:

    if (p.first >= 0) {
        normals[i] = triangles[p.first].normal();
        face_idx[i] = triangles[p.first].idx;
    } else {
        normals[i].setZero();
        face_idx[0] = -1;
    }

It turns out that p.first is not the index for the input faces.