# Entropie – rules for changing the code

Do's and don'ts that keep the game clean and quick. Short on purpose: add a
rule when a mistake shouldn't happen twice, drop one when it no longer holds.
Structure: [ARCHITECTURE.md](ARCHITECTURE.md).

## Do

- Keep the layers: `render` never includes `world`, `people` or `game`.
- Turn things with the helpers in `math/linalg.h` (`yaw_facing`, `yaw_along`,
  `yaw_front`). Fronts are +Z, lengths are +X.
- Tunables as `#define` at the top of the file, with unit and meaning.
- Ask "what's near" through the `Grid`, rays through `World_rayCast` /
  `Collider_ray`, the ground through `World_groundHeight`.
- Static things go in before the terrain; things lying on the ground are
  placed after it (`Scene_finish`, `Site_finish`).
- A new building part: `manor.c`'s `Plan` (boxes, walls with gaps, openings).
- Rebuild a mesh only when what it shows changes.
- Compile without warnings: `-Wall -Wextra -Wpedantic -Wshadow`.
- Characters moved by script (stepping over, onto, sitting down) use the set
  moves, never a jump of the position. Feet set down by script: the surface
  plus `BODY_ANKLE_Y` (scaled), not the ankle's height of the moment.
- A collider's "up" face can be any of its axes (things lie on their side).
- Every version: bump `VERSION`, update `STATE.md` (done items out of the to-do
  list, version line at the end), keep `README.md` short (a few lines per
  area: the details go into `STATE.md` "Playing it"), write
  `commit_message.txt` with this version's changes only.

## Don't

- No `atan2f` for a yaw in new code, no `mat4_rotate_y` for an object's turn.
- No allocation per frame, no loop over all objects inside a loop over all objects.
- No reusing another kind's fields for a new meaning: add a field, say whose it is.
- No moving static objects behind physics' back (use their own function, then
  `Object_syncColliders`).
- No game rules in `render`, no input handling in `world` or `people`.
- No snapping a character up more than a stair (`SNAP_UP_MOST`).
- No copying a slab test, ray or spring: there is one of each (`Collider_ray`,
  `springStep`).
- README: never name Ubuntu (Debian or "any Linux"), always the
  "100% Vibecode – but tested" line, no extra files nobody asked for.