Entry 161

The lakes' sky and fireflies: DrawBG and SetRoom's FIREFLYs

2026-09-26world

Filescrates/piney-world/src/dungeon_area/lake.rscrates/piney-world/src/field_firefly.rscrates/piney-world/src/field_ambient.rscrates/piney-world/examples/dungeon_probe.rstools/test_dungeon_rt.pycrates/piney-game/src/session/tests/dressing.rs

The lake dungeons (types 8 and 9, field type 4) had no sky, and their fireflies were listed as not ported. Both are done now. docs/engine/dungeon.md, "The lakes' sky and fireflies", has the details.

The constructor makes the sky's clumps from the dungeon's own file, by GetBG:

• type 8: CMP_o_bac_l{n}_, bac_m, clo_l and clo_m;
• type 9: bac_l, bac_m, ero_l, ero_m and ero_s.

Each is unfogged. Their models are domes about 12,000 across. DrawBG draws them at the room's centre on the five lowest layers (-100 to -60), scaled 0.5, 1 or 1.5 by the room's size. It also scrolls one material's V by 0.003 a frame (the clouds). That scroll is one static for the whole game. The room's pieces are drawn over the domes, so the sky shows only above the walls and through the doorways. A picture with only the first eight draws kept showed the domes were there all along, behind the forest.

By night (GetTime 2, which for field type 4 is bgnum 2) or with ishack at 3, SetRoom ends by making five FIREFLYs. Each gets its constructor's pattern, then a base up to 1,000 on from the room's centre in x and y (so all five sit in one quarter of the room), then the field's SetBasePosition and Init. Their sprites come from field_eff, which the constructor keeps at +0x34c. DrawEff moves and draws them after the glows, as the field's FIREFLYs. One thing had to change for that: the firefly code took the field's bounds (48,000) as a constant, and a dungeon's are 60,000. field_ambient::Env now carries its bounds.

tools/test_dungeon_rt.py's new test_lake_night runs six lakes:

• four of type 8, by night and hacked;
• two of type 9 (sd9, hacked, by day).

The harness now decodes field_eff beside the dungeon's file and sets ishack and +0x34c. It makes the constructor's clumps itself (new ccClump, Init, SetFogSw) before calling DrawBG. Results:

• 51 rooms of SetRoom fireflies;
• 960 frames of DrawEff with them, with the player at a room's centre and then 4,000 off, which sends them back about him;
• 480 frames of DrawBG: the V halfword and every clump's matrix.

There were 0 mismatches. Two things came up on the way:

• A firefly's base w is whatever SetRoom left on its stack, so only xyz is compared.
• sd9 holds bgnum 0's clumps alone. The one way to a type 9 lake is story area 14's words, so no other bgnum reaches it.

piney-game's a_lake_by_night_has_its_sky_and_fireflies enters a Δ lake of bgnum 2 and checks three things: the frame's first four models are the sky's, the scroll runs, and the fireflies fly.