27 addresses, indexed by Z code (0 candidate above, 1 overlap, 2 IY above) + Y code (0 candidate further back, 3 overlap, 6 IY further back) + X code (0 IY further back, 9 overlap, 18 candidate further back). "Further back" means further from the viewer: smaller X, larger Y, lower Z.

Three outcomes. iy_goes_first when IY is behind or level with the candidate on all three axes and strictly behind on at least one: IY must be drawn first. candidate_already_first for the mirror image, where the candidate is behind IY -- it is already being drawn first, so nothing to do. order_unconstrained where each is in front of the other on some axis, which says nothing about their order. The last two are the same instruction; the table distinguishes them only in which entry it names. Index 13, overlapping on every axis, goes to objs_coincide.