Used by the routine at ENTER_ROOM.

Finds the robot's room in ROOM02, stepping from record to record by the count at +1, and takes its ink (ROOM_INK), the address of its colour byte (ROOM_COLOUR_AT), and its half-sizes and floor from ROOM_SIZES. Then it fills the records from record 4 (ROOM_OBJECTS) up, backgrounds first, then objects, and clears every record after the last it filled. A room that is not in the directory gets no records at all. Called by ENTER_ROOM on entering a room; the first four records -- the robot's two and the two for the places -- are not touched.

Backgrounds: a byte each, up to an $FF. A background (BACKGROUND_TABLE) is a list of eight-byte pieces -- graphic, U, V, Z, the half-sizes, the height, flags -- ended by a zero, each piece its own record, with this room as its +8.

Objects: groups, each a header byte (bits 0-2 how many less one, bits 3-7 the template) and a position byte for each. A template (OBJECT_TABLE) is a list of five-byte pieces -- graphic, the half-sizes, the height, flags -- ended by a zero, each piece its own record at the same place: U = 72 + 16 times bits 0-2 of the position, V = 72 + 16 times bits 3-5, and Z = the floor + 12 times bits 6-7.

Two templates are not templates. Template 31 moves TEMPLATES_AT on 64 bytes, to the second page, and the byte after it is skipped (twelve times in the rooms). Template 0 makes the byte after it the placement nudge (PLACE_NUDGE) for the groups that follow: its bit 0 adds 8 to U, bit 1 adds 8 to V, and the rest is added to Z. The rooms use it 42 times, 41 of them with $30, which raises the objects that follow by 48 -- four levels -- and once with 0. Pentagram's builder has the same code for the nudge but no jump reaches it; in Alien 8 it is live.

The count at +1 of the room's record, of the bytes from there to the end, is what stops the build, not the data: the backgrounds can use it up, or a group be cut short. Nothing checks that the 52 records are enough; if a room overran them the clearing loop, which stops only when it reaches the end of the records exactly, would not stop. None does: every room was built in the build's sessions.