Used by the routine at REDRAW_OBJECT.

Called by REDRAW_OBJECT when the list that CULL_OBJECT built at page $DA has something to draw (bit 1 of IY+$71). The list holds record numbers; IY+$7F the index of the last. Krumlinde's name for it is RTN_Sort_And_Draw_Sprites.

First the list is sorted. For each place in turn, the entries after it are tested against the one there with IS_IN_FRONT; if one of them stands in front of it, the entry is taken out, the rest close up, it goes on the end, and whatever now fills its place is tested in turn. The list is drawn from the end back, so each object is drawn before anything in front of it. An isometric scene has no single depth to sort by, and three objects can each stand in front of the next; the fifty moves allowed at each place (IY+$7E) are what stop such a ring from sorting forever.

Then the list is copied up to IY+$46, since the pages it lies in are about to be cleared -- thirty bytes whatever its length, over the printer's position and the room origin, which are wanted only while printing or drawing a room -- and drawn: each object's cover is ORed into page $DA and cleared out of page $DB (mode 4), and its image ORed into page $DB (mode 8). So page $DA ends up with where the objects behind cover the region, and page $DB with what they show, nearer over farther. In an ordinary pass the entries at the back of the list that are scenery or doors are skipped, because the clean copy the compositor starts from already shows them; from the first live object on everything is drawn, scenery included, since it has to cover that object. In the scenery pass everything is drawn.