24 addresses, one for each background a room record can name. Each points at a list of 8-byte records ended by a 0 byte, and next_bg_obj_sprite copies each record as it stands into bytes 0 to 7 of a new object record: type, x, y, z, size along x, size along y, height and flags. It sets +8 to the room number and clears the rest. Unlike a block type, a background carries its own coordinates, so it is always in the same place in a room.

North is towards larger y and east towards larger x: the north arch stands at y = $C4, just beyond the far side of a full-depth room, and the east arch at x = $C4. Only the north and west sides have walls; the south and east sides are open towards the viewer.