This is an implementation of [1]: Given a 3D voxel grid, a starting position and an ending position in 3D space, we shoot a ray from the starting position to the ending position. This algorithm then lists all the voxel ID's being traversed by the ray.
[1] J. Amanatides, A. Woo, A Fast Voxel Traversal Algorithm for Ray Tracing, Eurographics'87