Entry 240

Which rests on which, and GRAB's choice, as the original's

2026-10-2357mplay

The stacking rule (0x8006c7a0) is decoded, ported and checked against the original. A thrown thing now rests on what its flight met, and GRAB now chooses its target as the original's 0x800631d8 does.

The flight's +0x98.

• It is the last object the flight met that is not a character (object flag 0x4000). 0x80087594 and 0x80086ef0 set it at each meet.
• The port's Thing::last_hit kept the opposite: the NPC or the player hit. Nothing read it, and bounced was never read either.
• Both are replaced by met (+0x98) and on (+0x70). Game::loads holds the +0x74 lists.

0x8006c7a0 (objectives.md, "Which rests on which"; things::stacking). For each of a's boxes:

1. The box's middle goes into the world, then into b's frame.
2. A b box holds it, grown across by the larger of the box's half-width and half-depth, and up and down by 3/4 of its height.
3. The two half-heights then decide: 2 (b on a) or 1 (a on b).

The original's quirk is kept: once one box was inside, a later box is judged by b's last box.

Checked. things_stack_as_the_original in tests/hle.rs moves thing a about thing b on a grid and compares each answer with the original's. It calls 0x8006c7a0 through call_nested.

• Level 3: planks and tipped pillars, 5 pairs.
• Level 6: boxes, 2 pairs.
• 34587 calls in all, 5460 answers not 0, none off.

The think's answers (0x8004df94 at 0x8004e018 and 0x8004e030):

• 1: the thing rests on what it met and joins its load.
• 2: the object's +0x74 is made of the thing's list plus itself, and its +0x70 is the thing's. That list is empty, so the object ends up bearing itself and can never be touched again (come_to_rest).

The pick-up (0x800601e4): the thing leaves what it rested on, and what rested on it falls oldest first (0x80062928: (0, 0, 4096) unturned, at speed 10).

GRAB (0x800631d8, touched):

• It skips a thing bearing a load.
• Going down the list, a thing whose first box rests on the nearest so far is taken over it at any distance. The nearest is forgotten even when the new one is out of reach. A thing under the nearest is passed over.
• The reach is now in integers:
  • the floor square root across (0x8001f4ec);
  • the way's VectorNormal and ratan2 (0x8009f278, 0x800760f4) against the heading, strictly within D_800c430a.
• The port had used a float hypot and atan2.
• touched_any skips doors and placed objects bearing a load.

Also:

• tests/flights.rs had not built since worklog 238, when Flights::step gained its meets argument; the suites only ran lib, play and hle. It builds again. Its a_thrown_thing_knocks_parts_off had set a thing flying with no flight record, which the record flights (flown) never move; it now starts the flight with start_flight. Every test file passes, and the hle suite (39) passes too.
• examples/stack_check: one thing put down onto another on both, with the oracle's think and the 0x8006c7a0 calls hooked.