Entry 191

"A lake's two dungeons: each kept by its number, lastRoom, and the way back up (GoField for field type 4)"

2026-09-26world

Filescrates/piney-world/src/dungeon_area.rscrates/piney-world/src/field_world.rscrates/piney-world/src/evarea.rscrates/piney-world/examples/dungeon_probe.rscrates/piney-game/src/session.rsdocs/engine/dungeon.mddocs/engine/field-walk.md

field-walk.md listed "GoField for field type 4 ... is not ported; what sets +0x100 is not traced". Field type 4 is the lakes, and Infection has plenty of them:

• seven words make one ("Solitary", "Haunted Land", "Feeling", "Remains", "Seeding", "Valkyrie", "Emerald");
• so do story areas 33, 48, 72 and 103.

A lake has no field. Dungeon 0 is the lake itself; dungeon 1 is below it, of dungeonType[1] = 2.

What the game does (read):

• WORLD_MAN::Enter on the lake's stairs down (0x0019e238) clears +0x58[game.dungeon] and sets lastRoom (+0x100) to game.block. It then calls ChangeScene(2, -2, -2, 1, 0, 0).
• On floor 0's stairs up of a field type 4 area (0x0019e0f8), and from menu 86's GoField in dungeon 1 (0x0019e440), it clears +0x58[game.dungeon] and calls ChangeScene(2, -2, -2, 0, 0, lastRoom). GoField in the lake itself does nothing.
• GO(2) keeps each dungeon by its number (dungeon[3] at +0x438) and makes one only where the slot is empty. Its last branch applies with field type 4, dungeonPrev 1, block == lastRoom and dungeon 0: it puts position at the lake's startpos[1][0], then ClearRoom and SetRoom(0, lastRoom), with the seed kept round it and dungeonback 1.

dungeon.md had most of this already. So the only thing not traced was who sets +0x100: it is Enter.

What the port did. It kept one dungeon (Kept::Dungeon) and reused it for any scene of area 2 after one of area 2. So the lake's stairs down gave back the lake itself as "dungeon 1". The way up went to block 0, and GoField did nothing in a lake.

Now:

• dungeon_area::Dungeons holds the three slots and lastRoom, and Kept::Dungeon carries them.
• FieldWorld::enter takes the slot of scene.dungeon or makes that dungeon. On GO(2)'s return case it calls DungeonArea::come_back: level 0, the position at floor 0's stairs down, SetRoom(0, lastRoom).
• into_kept puts the dungeon played back in its own slot, by its own number, not the next scene's.
• DungeonArea::enter takes lastRoom. It sets it on the lake's stairs down and uses it on the stairs up.
• go_field does the field type 4 case.
• dungeon_probe keeps a lastRoom of its own. test_dungeon_rt.py passes (10 tests).

Checks:

• a_type_4_area_goes_down_into_its_second_dungeon_and_back (piney-world): the exits on both stairs, lastRoom, and come_back's room and position.
• a_lake_keeps_both_its_dungeons (piney-game): area 33 entered and left through AreaMode. The lake is kept while the second dungeon (not a lake) is made; on the way back both are there and the party is at the lake's stairs.