[Flags]
enum Sides : byte
{
    None = 0x00,
    Top = 0x01,
    Bottom = 0x02,
    Left = 0x04,
    Right = 0x08,
    Front = 0x10,
    Back = 0x20
}

public static Sides VisibleFacesFor(ChunkInfo chunk, IntVector3 voxel)
{
    var sides = Sides.None

    voxel.Y += 1;
    if (chunk.GetVoxel(voxel).Weight <= 0)
        sides |= Sides.Top;

    voxel.Y -= 2;
    if (chunk.GetVoxel(voxel).Weight <= 0)
        sides |= Sides.Bottom;

    voxel.Y += 1;
    voxel.X -= 1;
    if (chunk.GetVoxel(voxel).Weight <= 0)
        sides |= Sides.Left;

    voxel.X += 2;
    if (chunk.GetVoxel(voxel).Weight <= 0)
        sides |= Sides.Right;

    voxel.X -= 1;
    voxel.Z -= 1;
    if (chunk.GetVoxel(voxel).Weight <= 0)
        sides |= Sides.Front;

    voxel.Z += 2;
    if (chunk.GetVoxel(voxel).Weight <= 0)
        sides |= Sides.Back;

    voxel.Z -= 1;

    return result;
}