I've been playing around with Unity3d, seeing if I can make a voxel-based engine out of it (a la Castle Story, or Minecraft).

I've dynamically built a mesh from a volume of cubes, and now I'm looking into reducing the number of vertices built into each mesh, as right now, I'm "rendering" vertices and triangles for cubes that are fully hidden within the larger voxel volume.

The simple solution is to check each of the 6 directions for each cube, and only add the face to the mesh if the neighboring voxel in that direction is "empty". Parsing a voxel volume is BigO(N^3), and checking the 6 neighbors keeps it BigO(7*N^3)->BigO(N^3).

The one thing this results in is a lot of redundant calls, as the same voxel will be polled up to 7 times, just to build the mesh.

My question, then, is:

Is there a way to parse a cubic volume (and find which faces have neighbors) with fewer redundant calls? And perhaps more importantly, does it matter (as BigO complexity is the same in both cases)?