Cyclically Overlapping Surfaces:

Any number of overlapping polygon surfaces might be processed with this scan-line method. Flags for the surfaces are set to mention whether a position is inside or outside, and depth calculations are performed while surfaces overlap. While these coherence methods are utilized, we ought to be careful to keep track of which surface section is visible on each scan line. This works just if surfaces do not cut through or otherwise cyclically overlap each other as shown in Figure. If any kind of cyclic overlap is present in a scene, we may divide the surfaces to remove the overlaps. The dashed lines in this figure indicate where planes could be subdivided to make two distinct surfaces, so that the cyclic overlaps are removed.

Figure : Intersecting and Cyclically Overlapping Surfaces that Alternately Obscure One Another