jqueuniet/dm2-tools
1
0
Fork 0
Code Issues 2 Pull requests Projects Releases Packages Wiki Activity Actions

dm2-saves: convert_save passes Mac-endian SGB scalars, GlobalWords, timer fields, and cloud indices into converted saves untranscoded #172

New issue
Closed
opened 2026-07-04 15:15:16 +02:00 by jqueuniet · 1 comment
jqueuniet commented 2026-07-04 15:15:16 +02:00 (Migrated from codeberg.org)
Copy link

Problem

convert_save (convert.rs) endian-transcodes champions, the raw record arrays, the u16 tables (obj_link/obj_list/text), the map table, the decoded record-stream object bodies, and re-lays timer_count_raw — but the following decoded fields pass through in source byte order and are re-encoded bit-for-bit into the target save, where the target engine reads them with its own layout:

  • SGB scalars: game_tick, random_seed, last_creature_tick, last_action_tick, rain_next_special. Concretely, converting fixtures/mac-us/saves/skullkeep_void_gate to DOS produces a save the DOS engine reads with game_tick = 6,371,843 instead of 211,553 (~30× off), plus a scrambled RNG seed and tick timestamps. The engine uses these for timer scheduling and regen logic.
  • GlobalWords (64 × u16 quest/script state). All-zero in current fixtures, so latent, but any nonzero word converts ×256 off.
  • Timer fields: w_00 (tick-countdown low word), val_a, val_b. val_b of type-0x3c/0x3d timers is rewritten by phase 6 on load, but the rest goes straight into the target engine.
  • Type-7 val_b in timer-actuator link records (records.rs ~855, hardcoded LE).
  • 10-bit cloud indices (cloud_index, cloud-postfix values) — bit-permuted on Mac under the LE mask layout; transcode_record_stream_objects transcodes rec.data but never these. cloud_index is a timer-array index in the engine.

This is the conversion-side counterpart of #168: today the wrong interpretation and the missing transcode cancel out for round-trips but compound for conversion.

Why existing verification missed it

The Mac↔DOS↔Mac byte-exact round-trip is blind to interpretation (values pass through unchanged in both directions), and the semantic conversion assertions cover champions (whose accessors are byte-order-aware) plus record types/counts — not SGB scalars, global words, or timer payloads.

Fix direction

Once the decode layer interprets these fields byte-order-correctly, convert_save needs explicit transcoding for them (analogous to transcode_champion), and conversion tests should pin at least game_tick equality across a Mac→DOS conversion (decode source and converted output, compare semantic values).

May be related to previously observed converted-save runtime anomalies attributed to engine caps (black screen / frozen controls) — worth re-testing a converted save in DOSBox once fixed.

## Problem `convert_save` (`convert.rs`) endian-transcodes champions, the raw record arrays, the u16 tables (obj_link/obj_list/text), the map table, the decoded record-stream object bodies, and re-lays `timer_count_raw` — but the following decoded fields pass through in **source** byte order and are re-encoded bit-for-bit into the target save, where the target engine reads them with its own layout: - **SGB scalars**: `game_tick`, `random_seed`, `last_creature_tick`, `last_action_tick`, `rain_next_special`. Concretely, converting `fixtures/mac-us/saves/skullkeep_void_gate` to DOS produces a save the DOS engine reads with `game_tick` = 6,371,843 instead of 211,553 (~30× off), plus a scrambled RNG seed and tick timestamps. The engine uses these for timer scheduling and regen logic. - **GlobalWords** (64 × u16 quest/script state). All-zero in current fixtures, so latent, but any nonzero word converts ×256 off. - **Timer fields**: `w_00` (tick-countdown low word), `val_a`, `val_b`. `val_b` of type-0x3c/0x3d timers is rewritten by phase 6 on load, but the rest goes straight into the target engine. - **Type-7 `val_b`** in timer-actuator link records (`records.rs` ~855, hardcoded LE). - **10-bit cloud indices** (`cloud_index`, cloud-postfix values) — bit-permuted on Mac under the LE mask layout; `transcode_record_stream_objects` transcodes `rec.data` but never these. `cloud_index` is a timer-array index in the engine. This is the conversion-side counterpart of #168: today the wrong interpretation and the missing transcode cancel out for round-trips but compound for conversion. ## Why existing verification missed it The Mac↔DOS↔Mac byte-exact round-trip is blind to interpretation (values pass through unchanged in both directions), and the semantic conversion assertions cover champions (whose accessors are byte-order-aware) plus record types/counts — not SGB scalars, global words, or timer payloads. ## Fix direction Once the decode layer interprets these fields byte-order-correctly, `convert_save` needs explicit transcoding for them (analogous to `transcode_champion`), and conversion tests should pin at least `game_tick` equality across a Mac→DOS conversion (decode source and converted output, compare semantic values). May be related to previously observed converted-save runtime anomalies attributed to engine caps (black screen / frozen controls) — worth re-testing a converted save in DOSBox once fixed.
jqueuniet commented 2026-07-06 08:47:21 +02:00 (Migrated from codeberg.org)
Copy link

Fixed by #209 (merged into main).

Fixed by #209 (merged into `main`).
Sign in to join this conversation.
No Branch/Tag specified
Branches Tags
main
pages
No results found.
Labels
Clear labels
No items
No labels
Milestone
Clear milestone
No items
No milestone
Projects
Clear projects
No items
No project
Assignees
Clear assignees
No assignees
1 participant
Notifications
Due date
The due date is invalid or out of range. Please use the format "yyyy-mm-dd".

No due date set.

Dependencies

No dependencies set.

Reference
jqueuniet/dm2-tools#172
No description provided.