# Levels & the in-game editor — direction note

Status: **direction agreed, not yet built.** Captures a brainstorm so the next
session starts from the conclusion, not a cold read. Nothing here is committed
code; it's the shape we want and *why*.

## The pivot

The game is heading toward a **multiplayer twitch shooter**. Each match loads a
**fresh, isolated level**. Consequences that shape everything below:

- **Maps are hand-made, not procedural.** Procedural scatter is demoted to a
  *tool* (a starting-block generator), never the runtime map path. This is the
  whole reason the editor matters — the editor *is* the map pipeline.
- **Real authoritative server.** The server bakes the same map the clients do and
  runs the authoritative sim.
- **No in-world level switching.** You don't walk through a portal to another
  world; the match lifecycle loads a level at start. → **portals / transition
  triggers are explicitly not needed.**
- **Persistence and player carry-over are YAGNI** for now — but must not be walled
  off (see hedges).

## Naming: `Level` (data) vs `Scene` (runtime)

Agreed vocabulary — reads as **"bake a `Level` into a `Scene`."** Fits the
type + namespace convention.

- **`Level`** = the authored, serializable **data document** (what an earlier draft
  called `LevelSpec`). Pure plain data. The editor's output; the network's payload;
  the server's and client's input.
- **`Scene`** = the baked **runtime instance** — the assembled world you render and
  simulate.

**Repurposing note (so nobody trips):** today the names mean something narrower —
`Level` (`game/level.ts:69`) is a *bake output* and `Scene` (`renderScene.ts:19`)
is a *render-only, worker-cloneable subset*. Under the new vocabulary:

- The name **`Level` is freed** for the authored data document.
- **`Scene` grows** to be the whole runtime instance — it **absorbs** the colliders
  + live mob array + terrain sampler that currently hang off `Level`. The thing
  **cloned to workers stays a render-subset projection** of the Scene (no colliders,
  no live mobs — those are main-thread only), exactly as the current `Scene` already
  is. This collapses today's incidental `Level`/`Scene` split (main.ts copies
  fields across) into two clear things.

So the pipeline is:

```
generator(params) → Level (data)   →   bake(level, textures) → Scene (runtime)
   (a TOOL: script / editor / never runtime)        (the runtime path)
```

(`bake` is today's `buildLevel`, renamed and re-typed to take a `Level` document.
Namespace home — `Scene.from(level)` vs `Level.bake()` — is an open detail.)

## The spine: the `Level` document

One serializable, explicit map document is the center of gravity. Four consumers,
one artifact:

- **Editor** *writes* it.
- **Server** *reads* it — bakes headless, runs authoritative collision/sim.
- **Client** *reads* it — bakes the identical `Scene` to render + predict.
- **Network** ships it (or its id) at match start.

Because the bake is deterministic, server and every client bake **byte-identical
geometry and collision** from the same `Level` — so only the document (or its id)
crosses the wire, never geometry.

### The one real refactor

Today the map *definition* is module-level constants welded **inside**
`buildLevel()`. Split generation from baking: the generator *produces* an explicit
`Level`; `bake` consumes it. `bake` should treat the **explicit** document (a list
of placements) as canonical — the generator emits that form. This one cut serves
three futures at once: multiplayer sync, the editor, and (later) persistence.

## Build order

1. **`Level` document + `bake(level)` + the gen/bake split.** Pure `game/`,
   headless, unit-testable, **no UI, no netcode**. The whole foundation — do it
   first, on its own.
2. **Then, in parallel — both ride the document, neither blocks the other:**
   - **Editor** — in-engine, browser, `app/`. Emits a `Level` file.
   - **Server** — real authoritative, imports `game/`, bakes the `Level` headless.

## The editor shape

- **In-game, single-player, edit↔play toggle.** Same running client: an edit mode
  to author the `Level` live, and a button that flips to **play mode** and drops you
  into the environment you're building. "Everything works except multiplayer" —
  full local sim (player, mobs, collision, later weapons) runs in play mode; no
  server, no netcode in the editor.
- The play toggle is a **re-bake + mode switch** — a loading beat, not a hot path.
  So it may freely re-bake and even reuse the existing worker respawn/`reconfigure`
  path; there is **no match, so no live-worker-resync problem** (the one genuinely
  hard sub-problem, thereby dodged).
- The engine already provides the hard parts: live first-person view, deterministic
  bake, and `camera` + `Terrain.height` for "where's the ground under the cursor"
  (raycast/picking). The remaining weight is **UI/interaction**. AGENTS.md notes
  "no DOM-built UI yet (deliberate)" — the editor is where that ends.

## Editor features (the brainstorm)

Three feature buckets. For each: what's already there, the real new work, the catch.

### 1. Sidebar tree — level config + contents

A **property inspector over the `Level` document.** If the document is clean data,
the tree is literally a view of it: each node = a field or an instance; edit a
field = mutate the document + re-bake.

- **World config already exists as data**, just scattered: `SkyConfig`, the
  `CloudLayer` union (basicCumulus/fancyCumulus + params), `TERRAIN`
  (amplitude/frequency/peaks/inner/blend), `GROUND_UV`, room dims. Parameterizing =
  moving these constants into the `Level`.
- **The tree forces one categorization: world property vs client look-preset.**
  `RenderConfig` (internalWidth, colorDepth, dither, lodDistance, filters) is a
  *per-viewer PS1 dial* — stays client-side. Sky/clouds/terrain = per-map, in the
  document. But **fog + lighting live in `RenderConfig` today**, and in a shooter
  fog density = sightlines = a *gameplay/map* property → fog probably moves into the
  `Level`. Decide the world-vs-viewer line once, up front.
- **Re-bake blast radius varies wildly:** sky color = re-run sky, no chunk touch;
  one tree = re-bake 1–2 chunks; terrain amplitude = re-bake *every* chunk. For a
  tool, full re-bake per edit is fine to start; scope to dirty cells only if it janks.
- **Anti-overengineering line:** "everything parameterized" = *document completeness*
  (every knob is data — yes). It is **not** a mandate for a generic reflection-UI
  framework. Hand-wire panels for the handful of config sections; generalize to
  type-driven widgets only if it hurts.

### 2. Object tools — add / select / move / rotate

- **Add** — palette pick + raycast ground (`camera` + `Terrain.height`) → drop an
  instance record → re-bake. Easy.
- **Select / pick** — **no GPU picking needed.** Props bake to anonymous triangles,
  but the document retains the instance list with positions → **ray-vs-instance-bounds
  test in JS**, nearest hit wins. (Another reason instances must live on the document.)
- **Move** — drag → raycast ground → update `position` → re-bake touched cell(s).
  Crossing a chunk boundary re-bakes 2 (cell membership is by base position).
- **Rotate — the one real engine gap.** Props have **no orientation today** (Tree/
  Boulder/Bush/Flower carry position + seed + size, no yaw; only *mobs* have
  `heading`, applied live via `Mat4.compose`). Fix by **separating the per-instance
  transform from geometry-gen**: `build` emits the instance's **unique local-space**
  geometry (keep seed/growth = shape), and the **baker applies position + rotation +
  scale** when appending to the chunk mesh. This mirrors what mobs already do (TRS
  via `Mat4.compose`) — props become "unique local mesh × transform," baked-in
  (static) where mobs are live (dynamic). This is the non-trivial refactor the object
  tools demand; do it early since it touches every prop builder.
- **Gizmos** — the rasterizer draws textured tris only, **no line primitive.** A
  move/rotate gizmo (and selection highlight / wireframe AABB) needs either thin-box
  tris or a new line-draw path. **Start gizmo-less** (drag on ground = XZ move,
  scroll/key = yaw; tinted re-draw for selection) and add handles later.

### 3. Terrain brushes — elevation + texture (the biggest new capability)

- **Elevation needs a stored, editable heightfield** — the thing that doesn't exist
  yet. `Terrain.height` is a **pure analytic function** of noise params; a brush has
  nowhere to write. So: **the `Level` owns a height grid**; procedural gen
  *initializes* it; brushes edit it directly; `Terrain.height` bilinear-samples the
  grid. ("Seeding is a tool," made concrete — noise seeds the grid, then you sculpt.)
  - **Collision comes free** — player + mobs already sample `Terrain.height`, so once
    it samples the grid, gameplay collision follows. No separate collision bake.
  - **Welds still hold** — patches weld by sampling shared height at shared world
    positions; grid-as-source keeps that. Re-bake only the brushed cells.
  - Side effect: the room "hole" + flat-inner-clearing special cases **dissolve into
    authored terrain**. An arena may drop the room concept entirely — the map *is* the
    sculpted terrain.
- **Texture brush fits the engine shockingly well** — the chunk baker **already
  accumulates one mesh per material key** and the renderer draws by DrawGroup list.
  Ground is one `grass` material today; painting = ground goes to **N materials, each
  painted tri routed to its material's mesh by a per-vertex/per-cell material id** —
  the *exact* routing the baker already does for props. **No rasterizer change.** Hard
  edges between materials (no blend) suit the PS1 look; soft splat-blending would need
  per-pixel multi-texture rasterizer work — skip it, add later only if missed.

### Threads that cut across

1. **The `Level` document gains three responsibilities:** retain instance lists
   (pick/move), own an editable **height grid** (elevation), own a **ground-material
   map** (texture paint). All still pure data — the document grew, the architecture
   didn't strain.
2. **One engine refactor unlocks the object tools:** pull per-instance transform
   (pos/rot/scale) out of prop `build` into the baker — props become "unique local
   mesh × transform," matching mobs.
3. **Terrain flips from function to data** — analytic → stored grid. Biggest single
   change, but it's what "hand-made maps" *means*, and collision + welds fall out free.
4. **Almost none of this needs new *rendering*** — picking is JS, texture paint
   reuses per-material DrawGroups, terrain is more patch bake. The only genuinely new
   render bit is small + optional: **line-draw for gizmos/selection**.

## Why the architecture already fits (the two bets that pre-paid for this)

- **Deterministic bake** — the world is byte-identical from a `Level` every run →
  multiplayer world-sync is nearly free (ship the document, everyone bakes the same).
- **DOM-free `engine`/`game`, layering test-enforced** — the authoritative server
  runs `bake(level)` + sim with no renderer; `app/` is client-only glue. The layering
  seam already enforced (`tests/layering.test.ts`) *is* the client/server seam. Keep
  the `Level` document + `bake` in `game/`; editor UI in `app/`; server imports `game/`.

## Cheap hedges (do now, save pain later)

- The `Level` document is **pure serializable data** — no closures, no behavior baked
  in (behavior stays code, imported per-side, as `Entity` already does it).
- A `Level` has an **id/name** — "load level X" is a reference; later persistence keys
  off it for free.
- **Player state stays out of the `Level`/`Scene`** (already true) — carry-over later
  touches the player, never the map.
- `bake` eats the **explicit** document as canonical — keeps the recipe-vs-explicit
  network choice open.
- **No hardcoded buffer sizes** tied to today's world — mob/framebuffer sizing already
  re-runs on `setup`; keep it so odd-shaped match maps just work.

## Current-state facts the next session will need

- `buildLevel(textures): Level` (`game/level.ts:175`) is the single entry, called once
  in `app/main.ts`. Today's `Level` (`game/level.ts:69-81`) is a **bake result**
  (chunks/meshes/colliders/mobs) — under the new naming it becomes part of **`Scene`**;
  the authored **`Level` document** is the missing *input* half. `buildLevel` becomes
  `bake(level, textures) → Scene`.
- Placement (`placeTrees/placeBoulders/placeBushes/placeFlowers/placeMobs`,
  `game/level.ts:359+`) is procedural from fixed seeds + counts, fully deterministic.
  These become the **generator** (emit a `Level`) rather than running inside the bake.
- **Prop instances are discarded after bake** — only anonymous triangles survive in
  per-chunk per-material meshes (`buildChunks`, `game/level.ts:251`). No `level.trees`
  to iterate. The editor edits the **document**, then re-bakes — never mutates baked
  meshes in place.
- **Mobs are the exception** — retained live, simulated each frame, crossing to workers
  as packed floats. Add/move/delete is cheap, no worker resync (caveat: mob shared
  buffer sized once to `scene.mobCount` in `app/renderer.ts` — growing past it needs a
  re-`setup`).
- Instance shapes are already small plain records (position + seed + kind/size/color/
  growth) — editor-friendly, directly serializable. See
  `game/actors/{Tree,Boulder,Bush,Flower,Mob}.ts`.
- Prop geometry currently bakes **position into world-space verts inside `build`**, with
  seed/growth driving unique shape — hence the "separate transform from geometry-gen"
  refactor needed for rotate/scale (see Object tools).
- `Terrain.height` (`game/Terrain.ts`) is a **pure analytic function**, no stored
  heightfield — hence the elevation-brush needs a stored grid (see Terrain brushes).
- The render `Scene` (`renderScene.ts:19`) is the **render-only subset** already; the
  chunk baker already routes geometry to **one mesh per material key** — the mechanism
  the texture brush reuses.
- Workers hold a **one-time structured clone** of the render subset from init
  (`app/renderer.ts` `setup`); per-frame only camera/matrix/visible/mob buffers cross.
  Chunk-geometry edits reach workers only via a re-send (`reconfigure`→`setup`, respawns
  them — the same path keys 1/2/3 use). Fine for a mode-switch re-bake; would be the wall
  for live in-match editing, which we are **not** doing.

## Explicitly out of scope / dropped

Portals & in-world transitions · persistence · player carry-over · procedural as the
primary map path · any live-edit-during-a-multiplayer-match capability · GPU picking ·
soft terrain-texture blending (hard-edged materials first).
