# Module (asset type) A module is a reusable, stateless (or globally-stateful) Luau library that other code pulls in with `require()`. Modules are the unit of factored-out logic in a world: helpers, math libraries, format parsers, registries, shared algorithms. ## When to use one - You have logic you want to share across multiple components, services, scenes, or tools. - You have a registry, lookup table, or shared cache that callers all read from / write to. - You want a stable API surface (`M.fn`) other code can depend on. If the logic is bound to one entity, use a `.component`. If you want a named UI of fields rather than functions, use a `.preset`. ## Where it lives - Source: `/zero/source/.../<name>.module/` - Identity: the source path with `/` written as `.` and each segment's type suffix dropped — `/zero/source/demo/beats.module` is `demo.beats`, and `/zero/source/kit.package/beats.module` is `kit.beats`, the container's name kept and its `.package` suffix gone. `asset.create` returns this string, `asset.resolve(...).identity` reads it back, and the `require` forms below write it as `<identity>`. - Folder shape: - `init.luau` (or `init.lua`) — module body. **Required.** Returns a table (conventionally named `M`). - `README.md` — instance-level documentation. **Required.** - `.metadata` — agent-editable tags + free-form fields. **Required.** ## How to create one ```luau asset.create("module", "<name>") -- Creates: /zero/source/<name>.module/ -- init.luau (canonical `local M = {} … return M`) -- README.md (instance README template) -- `folder` places it in a subfolder of /source, and that subfolder -- leads the identity: `{ folder = "lib" }` produces `lib.<name>`. -- `into` authors it inside a resolved container (a package, a toolbox), -- whose own identity leads the same way: asset.create("module", "<name>", { folder = "lib" }) asset.create("module", "<name>", { into = asset.resolve("myPkg.package") }) ``` ## How it operates 1. **Registration.** Writing `init.luau` into a `.module/` folder indexes the asset and registers the module path with the resolver. 2. **Loading.** The first `require("<identity>")` runs the file's body and caches the returned table. Subsequent requires from anywhere return the **same table** — this is the shared-state lever for "module-local" registries. The body runs in an environment of the module's own: a name it declares without `local` is readable by the module's own functions and by no other script, so an export reaches its callers through the returned table and nothing else. Requiring a component's folder runs its chunk the same way, once, and its `update`, `start` and `public` stay in that environment; a component runs on an entity through `entity(id).component.add(name)`. 3. **Hot reload.** Editing the file re-runs the module body and folds what it returns into the table already loaded, so that table keeps its identity: a caller that captured it with `require` reads the new source's functions and values through the reference it already holds, and a later `require` returns that same table. A key the new source drops goes away; a key something set at runtime stays. The body's own `local`s start again from their initial values, so state that must outlive an edit lives in `modules.state()` (`guides { path: "core/scripting-and-tasks" }`). 4. **Identity resolution.** A module is reached by its `<identity>`, and where the caller lives decides which spelling of it resolves. For a module in a **world**, from a caller in that same world — another module, a component, a scene entrypoint, or an `execute` chunk: - `require("<identity>")` — the identity on its own, resolved against the caller's own root. It carries every folder segment, so a module created with `{ folder = "demo" }` is `require("demo.beats")`. - `require("@root::<identity>")` — the same root-relative resolution, written out. - `require(".sibling")` — a module in the same folder, by its bare name; `..name` steps up one folder, `...name` two. Logs, stack traces and hot-reload notices name that same module `@local.source.<identity>` — its key under the world source root. The `<identity>` tail of that key is the form above, so a trace reading `@local.source.demo.beats` is `require("demo.beats")`. For a module in a **library** — content under `/zero/source/libs/@<lib>/` — `@<lib>::` addresses that library's root from anywhere: `require("@builtin::modules.transform")`. Mounting a world as a library moves its files under such a root and flips the caller root to `@<lib>::`, which is what keeps the root-relative forms above resolving across the move. ## Discovery - `asset.list("module")` — every registered module. - `asset.inspect("<name>")` — public functions, source path, this type README. - `ls /zero/source/<name>.module` lists the files the folder holds. ## Authoring conventions - Return a single `M` table from `init.luau`. Top-level statements with side effects run on first require — useful for one-time initialization, dangerous if they touch the engine before it's ready. - Write exported functions as `typed function`, not `function`: the argument types are enforced at the call and the checker knows the signature, so a caller's mistake is reported where they made it. - Annotate exported functions with `--!desc` / `--!arg` / `--!return` / `--!example` so the LSP, `tools.list`, and `asset.inspect` surface them. A function with no `--!desc` is reachable only by someone already reading this file. - Declare a VALUE with `Field.<kind>(default, mode, description)`, and a table whose members are reached through a metatable with `--!members <TypeName>` — the latter gives the surface its accepted member set, its type, and its documentation from one table. See `guides { path: "core/authoring" }` for all four rules and `modules/api/engine/entity.module/members.module` for a worked member table. - Keep module state in module-local upvalues or in `modules.state()`. A name the body declares without `local` lives in the module's environment, which every run of the module shares: a function the previous run left in place reads what the reload assigned. Module-locals start again from their initial values with each hot reload; the table `modules.state()` returns is the same table on both sides of every reload. - Prefer focused modules over kitchen-sink modules. If two halves of a module have no shared state, split them. ## Common pitfalls - **Cyclic requires.** A `require` chain that loops will return the partial table (the half built before the cycle was detected). Design for one-way dependencies. - **Engine-time side effects.** Don't `entity.spawn` at module top-level — the engine may not be ready. Expose an `M.init` and call it from a scene entrypoint. - **Hot-reload + module-local cache.** A module that caches expensive computation in upvalues loses that cache on reload — fine for dev, but be aware in performance work. - **`init.lua` vs `init.luau`.** Either works, `.luau` is canonical. - **Writing one while play runs.** A `/source` write made while play is running lands on the play shadow, and a guarded play-exit discards it unless it is kept. One `.module` write shadows `init.luau`, the `README.md` and the `.metadata` together. `vfs.write(path, bytes, { durable = true })` skips the shadow, and `vfs.promotePlayShadow` keeps what is already on it — the `core/vfs` guide has the model and what each route costs. ## Related types - `.component` — for entity-bound state + lifecycle hooks. - `.service` — generates content you don't have yet (a mesh, sound, texture, …) via a metered provider. - `.tool` — for a single agent-callable function with a YAML schema. - `.package` — to group several modules + components + scenes into one shippable folder. ## In the Inspector Exports: what the module exports (name, kind, signature), parsed from its source without running it, with **Check** (the LSP's diagnostics for its entry file) and **Open**.

# terrainHeightfield A `.texture` standing over a rect of world, read as ground. The durable form of a landscape is an ordinary texture asset — one with a guid, that a component references, that travels with a world, that the renderer already knows how to sample. `terrain.to_texture` is what puts a graph's raster into one and `texture.write` persists it. This module is the other end: what a runtime holds while that ground is on screen. ```lua local terrainHeightfield = require("~terrainSystem.modules.terrainHeightfield") -- A `.terrainData` states the rect it covers, so opening one needs nothing else. local hf = terrainHeightfield.open("/zero/source/terrain/dunes.terrainData") -- The heightfield alone can be read too; then the caller says where it stands. local bare = terrainHeightfield.open(tex, { size = { 4000, 4000 }, origin = { 0, 0 } }) local y = hf:heightAt(120, -60) -- metres local nx, ny, nz = hf:normalAt(120, -60) local slope = hf:slopeAt(120, -60) -- radians hf:close() ``` ## The texels `rgba32f`, in the layout `terrain.to_texture` writes: | Channel | Holds | |---|---| | R | the height, in METRES — it goes negative | | G | the gradient along world X | | B | the gradient along world Z | | A | coverage | A height's interesting relief is often a few metres inside a range of hundreds, so eight bits band it into terraces; that is what the precision is for. The gradient is what a surface normal comes out of without differencing the height four more times, and it is why `terrain_mesh` costs four texel reads a vertex rather than twenty. A heightmap authored anywhere else — an 8-bit image, a downloaded elevation tile, a raster an earlier graph baked — becomes one of these by going through a graph: `terrain.from_texture` reads it as ground, and `terrain.to_texture` writes the result back out at this precision. ## Two carriers, one set of texels An open heightfield holds the texture in both forms the runtime reads it in: - **`hf.texels`** — a GPU buffer of the texel bytes, which the `terrain_mesh` compute kernel builds vertices out of. - **`hf.cpu`** — the pixels, which `heightAt` / `normalAt` / `slopeAt` / `sampleGrid` answer from. Both are the same texels, uploaded from one read, so what the ground LOOKS like and what a query SAYS about it cannot drift apart. The pixels are the heightfield's own copy, decoded from the asset when it opens and held in a buffer for as long as it stands, and so are its holes mask, its water surface and its layer weights. A heightfield answers in edit, in play and after play, whatever else loads or unloads the same texture. The cost is one copy a heightfield: 16 bytes a texel for the heights and the water, 4 for the holes mask and each layer-weight texture. Two heightfields open on one landscape hold two copies, which is also what keeps an edit to one (`setHeights`) to that one. ## The surface | Verb | | |---|---| | `open(ground, opts?)` | Read a `.terrainData` — or the heightfield `.texture` alone — as ground. A container carries its own `{ size, origin, heightRange }`; a bare texture takes them from `opts`, and an explicit opt outranks the container either way. | | `hf:heightAt(x, z)` | Bilinear metres. | | `hf:normalAt(x, z)` | Unit normal, three numbers, from the carried gradient. | | `hf:slopeAt(x, z)` | Radians; 0 is flat. | | `hf:sampleGrid(cols, rows)` | Row-major heights over the whole rect — the shape a heightfield collider takes. | | `hf:hasGroundAt(x, z)` | Whether there is ground at all — false over a hole. | | `hf:refresh()` | Read the texture's pixels again and put them back on the GPU. Bumps `gen`. | | `hf:close()` | Let go of the pixels and the GPU buffer. The asset is untouched. | `heightRange` is the vertical reach the geometry declares, which becomes the mesh's bounding box — a range smaller than the ground culls the terrain away at grazing angles. Left out, it is read off the pixels, which costs one pass over them. ## Holes A landscape can be CUT OUT — a cave mouth, a quarry, a shaft — and its holes mask is carried the same two ways the heightfield is: on the GPU for the index kernel, which writes the quads it cuts out as degenerate triangles, and on the CPU for `hasGroundAt`. Same pixels, so a place with no surface to draw is a place nothing can be stood on either, and scatter that asks before it places never drops a tree into a shaft. A landscape with no mask is solid everywhere and answers `hasGroundAt` true without reading anything. The edge of a hole follows the mask at the density the node is meshed at, so a hole is quad-shaped at the LOD it is seen from. ## Generations `hf.gen` counts the times the texels have been read. `terrainMesh` records the generation each node was meshed at, so re-authoring the ground under a standing terrain and calling `hf:refresh()` brings the geometry with it — nobody has to say which nodes changed.

# Terrain (component) Ground, as scene content. Part of the [terrainSystem package](../../readme.md) — every terrain entity in a scene carries exactly one of these. An entity carrying this component IS a landscape: a `.terrainData` standing over a rect of world, drawn through a quadtree of LOD nodes that refines under whichever camera is looking at it, with a collider the default avatar can walk. ```luau -- The whole of it: one reference. The landscape says how big it is. entity(id).component.add("Terrain", { terrain = dunes }) ``` ## Properties | Name | Type | Default | Description | |------|------|---------|-------------| | `terrain` | `AssetRef<terrainData>` | `nil` | The landscape this entity IS — the heightfield, the control textures, the holes mask and the layer table, held together as one asset. It states the rect it covers and the reach it declares. | | `material` | `AssetRef<material>` | `nil` | What the ground is shaded with. Falls back to the package's `terrainStandard`. | | `size` | `vec2` | `{ 0, 0 }` | Where the ground stands, when it should stand somewhere other than where the landscape says. Left at zero, the container's own placement is used. | | `origin` | `vec2` | `{ 0, 0 }` | World centre of that rect, same rule. | | `heightRange` | `vec2` | `{ 0, 0 }` | The vertical reach the geometry declares — `x` the lowest metre, `y` the highest. Left at zero, the landscape's own reach is used. | | `collision` | `boolean` | `true` | A static heightfield collider over the whole rect. | | `collisionResolution` | `number` | `257` | Collider samples along each axis. | `heightRange` is the mesh's bounding box, so a range smaller than the ground culls the terrain away at grazing angles and the symptom is nothing at all on screen. The collider is ONE grid over the whole rect, so `collisionResolution` is its spacing: 257 over four kilometres is a sample every sixteen metres, and raising it buys resolution at O(n²) cells to build. The heightfield's own texel count sets how finely the ground is described inside the rect; the landscape's `size` sets how much world that description covers. ## Where the landscape comes from A graph. It opens a rect of ground with `terrain.source`, shapes it with the terrain nodes (`fbm`, `cone`, `ridge`, `erode`, ...), writes the coverage of each surface as a mask layer with `terrain.mask`, and ends in `terrain.write`, which bakes the manifest and every child texture in one step and answers the reference to the `.terrainData`. That is the same move every other procgen family makes to persist what it made. The reference is what the component's `terrain` property holds: `entity(id).component.add("Terrain", { terrain = ref })`. A heightmap made anywhere else (an 8-bit image, a downloaded elevation tile) comes in through `terrain.from_texture` and back out through `terrain.write`. ## Lifecycle - `awake` — opens the landscape, builds the LOD pool, binds it to the entity, adds the `Model` and the collider. - `update` / `editorUpdate` — follows the on-screen camera with the cut, in edit and in play alike. - `onPropertyChanged` — a `material` change swaps the Model's material in place; anything else describes the ground itself, so the ground is rebuilt. - `onDestroy` — releases the mesh, the pool and the heightfield's pixels. ## Methods | Method | | |---|---| | `:heightAt(x, z)` | Bilinear metres. | | `:normalAt(x, z)` | Unit surface normal, three numbers. | | `:slopeAt(x, z)` | Radians; 0 is flat. | | `:field()` | The heightfield itself — the value every `terrainHeightfield` verb takes. | | `:reload()` | Read `terrain` again and rebuild what the entity draws. | The queries answer from the same texels the geometry is built out of, so what a script is told and what a player walks on cannot disagree. Re-baking the landscape and calling `:reload()` moves every terrain standing on that asset, without a restart and without touching the scene graph — the mesh keeps its guid, so the Model is never re-bound. ## One draw Every node of the LOD cut is one range of one index buffer, so the whole terrain — at every level, however large — is a single indexed draw on a single entity. Nodes are never entities. `modules/terrainMesh` is the whole surface.

# pathNetwork.geometry The shape of a path network, as pure functions over plain tables: the centreline of an edge through its control points (a Catmull-Rom curve whose end tangents are shared with the next edge across a node), the cross-sections along it (position, heading, bank, the surface's right and up), and the meshes `pathNetwork` stands on entities: an edge's surface with side walls and end caps, and a junction's surface fanned out to the ends of the edges meeting there, sharing their vertices. | Function | | |---|---| | `centreline(control, before, after, step)` | Sample a curve through the control points finely enough to measure it. | | `at(line, d)` | The point a distance along a sampled centreline. | | `sections(line, spec)` | Cross-sections between two distances, each with its surface frame. | | `smooth(ys, window, opts)` | A moving-average elevation profile, its window full and centred on each sample (`lead` and `trail` samples of ground past the ends), each held end meeting the height and grade given through a cubic ease that adds no more than `maxGrade` and bends the grade no faster than `maxBend` per metre. | | `edgeMesh(sections, opts)` / `junctionMesh(centre, ends, opts)` | Geometry for `renderer.mesh.create`. | | `project(a, b, x, z)` / `surfaceHeight(a, b, t, lateral)` | Where a point lies against a segment, and the surface's height there. | | `fanHeight(centre, ring, x, z)` / `fanDistance(centre, ring, x, z)` | A junction surface's height over a point, and how far outside its outline the point stands. | | `corner(section, side)` | A surface edge of a cross-section (`side` -1 left, 1 right). |

# assetType (asset type) An asset type says what a kind of asset is: the files an asset of the kind is made of, the code that gives it behaviour, the interface a person uses to work with it, and how it is found, pictured and checked. A `<typename>.assetType/` folder declares a type called `<typename>`, and every `<name>.<typename>/` folder is an asset of it. `assetType` is itself a type, so a type is an asset like any other: it is created, versioned, installed and contributed the same way. ## Making a type `asset.create("assetType", "<typename>")` scaffolds a type. The type registers the moment its folder is written, anywhere under `/zero/source/`, and from then on `<name>.<typename>/` folders are its assets. An asset of a type that is not registered yet is not an asset, so make the type first. A type folder is a root: `~.x` in any file inside it names the type's own `x`, wherever the type is installed. Keep the type's whole implementation inside its folder and reach it that way. What a type folder must hold is set by this type's own `type.yaml`, the same way every type's `type.yaml` sets what its assets hold. `asset.validate` on a type reports anything missing, and the scaffold produces a folder that passes. ## What sets your type's schema (`type.yaml`) `type.yaml` is the structural contract every asset of the type is checked against. The keys below are the ones the engine reads; a key not listed here is ignored. | Key | What it controls | |---|---| | `suffix` | The folder suffix of the type's assets. Defaults to `.<typename>`. | | `primary` | The file or files that are the asset's content: what the asset resolves to when it is used. | | `entry_files`, `primary_aliases` | Further files that load as the asset or share its identity. | | `is_container` | Whether the suffix stays in the identities of what the asset holds. | | `is_opaque_walker` | Whether a walk of the tree stops at the asset and registers only its primary. | | `plural_dir`, `classify_exts` | Loose files in a folder of this name, or with these extensions, are assets of the type. | | `is_text_default` | Whether the asset's files are text unless stated otherwise. | | `broadcasts_subassets` | Whether assets nested inside an asset of the type are found by their own short name. | | `root` | `true` makes every asset of the type a root, so `~.x` inside one names that asset's own `x`. | | `contract_ref: { field, category }` | A key of the primary file that names another asset the asset is built on. | | `files: { required, optional }` | The files an asset holds (below). | | `allow_unlisted` | `false` reports every file the type does not declare. | | `aliases_from: [{ file, key }]` | Further names an asset answers to, read from its own files. | | `settings:` | Typed per-asset settings (below). | | `inspector:` | The interface people use for the type and its assets (below). | | `preview:` | How an asset is pictured (below). | | `references:` | Names of other assets the type's files carry (below). | | `indexing:` | What search reads for each asset (below). | | `describe:` | How a missing description is generated (below). | ### The files an asset holds Each entry under `files.required` or `files.optional` is `{ path, kind: file | folder, one_of_group?, content? }`. `*` in a path matches within one segment. Entries that share a `one_of_group` are satisfied by any one of them. `content` lists checks on the file's bytes: | Check | Passes when | |---|---| | `non_empty` | the file has content | | `json_field { key, type?, non_empty?, accept? }` | the JSON holds the key (a dotted path) with that shape | | `yaml_field { key, type?, non_empty?, accept? }` | the same for YAML | | `described { keys?, headings?, message? }` | the file says what the asset is (see "Ask your assets to say what they are") | Each check takes a `message`, which is what the author is told when it fails. ### Settings `settings: { values, schema: { type | instance, export? } }` gives every asset typed settings. `values` names the file an asset's values live in; `schema.type` declares one schema for the whole type, and `schema.instance` names a file each asset declares its own in. `asset.create` writes the resolved values, and a write to the values file reaches `onChange` with what changed. ## The human side (`inspector.luau`) A type is used by people through its Inspector, and without one the type is usable only from code. The Inspector is the type's interface for a person: for a procedural graph it is the graph editor, for a kit it is the tracking view of what the kit holds and what is still missing. Writing it is part of writing the type. `inspector: { type, instance? }` in `type.yaml` names the files. `type` is the interface for the type itself and for its assets; `instance` names a file an asset may ship to add its own. Each returns: ```luau return { sections = { { id = "graph", title = "Graph", build = function(ctx) ... end } }, replace = { contents = { ... } }, -- replace a default section by id order = { "graph", "contents" }, -- section order } ``` `build(ctx)` receives the asset and builds the section. A section's `title`, and the text its rows carry, is a string or an `i18n.text` value read from a catalog (`i18n.text("inspectors.mesh.title")`), which follows the editor's language. `asset.create("assetType", ...)` scaffolds a working `inspector.luau` to start from. `asset.validate` on a type that names no inspector, or names one that does not load, reports it. ## Say what your type is for (`about.yaml`) Every type carries an `about.yaml` that says what the type is for, in three plain-language texts: ```yaml intent: "Sets the typeface of the text in your game: UI, labels, signs and 3D lettering." function: "A font, from a TTF, OTF or WOFF file, made available to all of Zero's text, including 3D text." usage: "You choose it by name for your UI or your text, and the text appears in that typeface." ``` - **`intent`** is what the type is for in someone's game, in the words a game maker uses. Up to 800 bytes. - **`function`** is how it works today: what an asset of it is made of and what the engine does with it. Up to 1500 bytes. - **`usage`** is what a person or an agent does with one. Up to 1200 bytes. Write about the type as a whole, not one asset of it, and say what it does now. Agents read these texts to learn when to reach for the type and how; people searching find the type by them. The scaffold starts each text with `[[describe]]` and a note on what to write; a text that still starts that way counts as not written. `services describe` can write them. They show up in `asset.inspect` as `detail.about`, in `assetTypeRef:getAbout()`, at the end of the type's `types/<typename>` guide, and at the top of the type's Inspector. ## Ask your assets to say what they are A type can require each asset to carry a description: a file, written by the author or generated, saying what the asset is and what it is for. Declare it with a `described` check: ```yaml files: required: - path: "README.md" kind: "file" content: - { check: "described", message: "Say what this widget is for and where it goes." } ``` A file that is missing, empty or still has a line starting with `[[describe]]` fails the check, and so does a YAML file whose named `keys` are missing or over their `max_bytes`, or a Markdown file missing a named heading. `asset.validate` names the asset, and a push that carries it is refused with `message`. `services describe` finds such assets and writes their descriptions. `describe:` steers what is generated: ```yaml describe: guidance: "Say what the widget shows, what input it reacts to, and where it fits in a UI." examples: - "<identity of an asset of this type whose description reads well>" ``` An example is an asset of your type whose description is a true, written one, never a placeholder and never the asset being described; with none, leave `examples` empty. A type whose assets the model cannot perceive (a sound, a motion) says so in `guidance`, and the description is drawn only from what the asset's own files state. Start the file unwritten in your `template/`: a heading and one line starting with `[[describe]]`, never example content, which every new asset would carry verbatim. A type whose assets say what they are through their own content (a mesh, a texture) declares no check. ## The type's code (`behavior.luau`) `behavior.luau` returns one table. These are the keys the engine reads from it; anything else on the table is the type's own. ### What the type's assets can do | Key | Shape | What the engine does with it | |---|---|---| | `ref` | `{ [name] = function(self, ...) }` | Every function becomes a method on every asset of the type: `ref:name(...)`. | | `modules` | `{ [name] = require(".x") }` | Code the type's assets reach with `asset.containing(__FILE__).modules.<name>`. | | `events` | an events schema | Events an asset fires. Readers subscribe through `ref.events.<name>:connect(...)`; the type fires them. | | `refShapes` | `{ [method] = function(self) -> (typeExpr, source?) }` | The result type of a `ref` method for one particular asset (below). | | `namePattern` | a Lua pattern | The names `asset.create` accepts for the type's assets. Default `^[A-Za-z][A-Za-z0-9_]*$`. | | `derive` | `{ output, module, compute, fingerprint, matches?, required?, timeout? }` | A file computed from the asset when it is committed; a `required` one holds the commit until it lands. | Some `ref` names mean the same for every type, and the engine calls them: - **`instantiate(self, target?, opts?) -> (root, idMap)`**: puts the asset in a scene. Defining it is what makes the type scene-instantiable. Its return is a contract (below). - **`inspect(self) -> detail`**: what `asset.inspect` reports for the asset beyond the common record (below). - **`preview(self, opts)`**: renders the asset's picture; it wins over the type's `preview:` recipe. - **`previewMaterial(self) -> { material }`**: the material a `surface` preview paints. - **`saveDefinition(self)`**: writes the asset's in-memory edits back to its files in edit mode. Some names are answered for every asset before the type is asked, so a `ref` entry of the same name is never reached: `getSource`, `getBytes`, `getText`, `exists`, `deps`, `canInstantiate`, `canPreview`, `preview` (which calls yours when you define one), `meta`, `runtime`, `events`, `typeRef`, `modules`, and the residency flags `has_backing_asset`, `has_runtime_changes`, `cpu_resident`, `gpu_resident`. ### When the engine calls the type | Hook | Signature | When it runs | |---|---|---| | `onCreate` | `(name, opts) -> { [path] = contents }` | On `asset.create`. Returns the files of the new asset, laid over the type's `template/`. Annotate `opts`: its type is the schema `asset.create` checks the caller's arguments against. A `""` key writes a single loose file. | | `onReplace` | `(dest, files) -> files` | On an `asset.create` over an asset already at `dest`, after `onCreate`, so what the author added can be carried into the replacement. | | `onRegister` | `(self)` | Once per asset, when it first registers: when the world loads, on a live `asset.create`, and when an asset arrives later (installed, pulled, synced). This is what makes an asset take effect the moment it is written. | | `onChange` | `(ref, change)` | On every write to a file inside an asset of the type. `change` is `{ path, asset, type, kind, origin }`, plus `settings` and `settingsChanged` for a write to the settings values file; `kind` is `edited` or `seeded`, `origin` is `local` or `remote`. Filter on `change.path`. Writes to one asset arrive in order, each after the hook for the one before has finished, and the hook may wait on what it reads. A write the hook makes inside its own asset arrives later like any other, so keep the hook convergent. | | `onDependencyChange` | `(ref, change)` | When a module the asset's code requires is re-run, or a name the asset carries starts resolving. `change.kind` is `dependency`. | | `onDelete` | `(ref)` | When an asset of the type leaves the world: deleted, or the world it is in is swapped away. | | `validate` | `(ref) -> { { code, message, severity?, path? } }` | On `asset.validate`, after the `type.yaml` checks, for the type's own rules. `severity` defaults to `error`. Runs on every push, so a type's rules hold at publish. A hook that fails reports `validate.hook_failed`. | ### Settings hooks | Hook | When it runs | |---|---| | `settingsDefaults(name, opts, asked) -> table` | Once per `asset.create`, for values the schema's defaults do not give. | | `settingsCorrections(values, name, opts) -> (corrections?, reasons?)` | On every settings write. A correction to a field the writer named refuses the write, giving the reason. | | `settingsDerivedDefaults(values, explicit, changed)` | On a settings write, for fields derived from others. | | `normalizeSettings(values, stored?)` | On every read and write, to map an earlier spelling of a field to the current one. | | `settingsHealed(values, stored)` | On a read, to repair stored values. | | `settingsSchemaProblem(schema, ref) -> string?` | When an asset's own schema is read; a returned string refuses the schema. | `creationInputs` (`{ [opt] = true | selectorOpt }`) names `asset.create` options that are inputs to the type rather than settings. ### Reloading An edit to `behavior.luau` reaches existing assets with no restart. ## How an asset is pictured (`preview:`) | `kind` | The picture is | The type provides | |---|---|---| | `instantiate` | the asset placed in the preview studio through its `instantiate` | `ref.instantiate` | | `image` | a file the asset holds, fitted to the frame | `source: { files }`, the candidate files in order | | `surface` | the asset painted on a mesh | `mesh`, and `ref.previewMaterial` | | `custom` | whatever `ref.preview` returns | `ref.preview` | ```yaml preview: kind: surface mesh: sphere ``` `angle: [yaw, pitch]` turns the camera. The studio owns the light, the backdrop and the framing, so an asset pictures the same in every world. A type with no `preview:` that defines `instantiate` still answers `ref:preview()`. A picture is rendered when something asks to view it (the editor showing the asset, `ref:preview()`), when previews are generated on request (`assets.generatePreviews`), and when the asset is staged. An edit alone renders nothing. The picture records what it was made from, so a stale one is told from a current one. ## The names your type's assets hold (`references:`) Where your type's own format or API carries the name of another asset, declare it here: ```yaml references: keys: # a top-level key of the type's files that holds a name, or a table of them - { key: "shader", type: "shader" } args: # an argument of a call, counting from 1 - { call: "g:node", position: 2, type: "procNode" } fields: # a field of the options table a call takes - { call: "fx.beam", field: "material", type: "material" } ``` `type` is the category the name resolves in. `asset.declareReferenceKey`, `asset.declareReferenceArg` and `asset.declareReferenceField` declare the same from a script. ## What search reads (`indexing:`) `indexing:` is how assets are found. Search reaches an asset only through what its type's `indexing:` names, and adds nothing of its own. That includes you: an asset indexed badly is one you cannot find later, when you are making something else and need it. A type whose assets are never looked for says `indexing: none`. ```yaml indexing: data: # text, read from the asset's files - role: identity extractor: verbatim source: { file: "README.md" } - role: interface extractor: symbols source: { files: ["init.luau"] } - role: implementation extractor: verbatim source: { files: ["init.luau"] } content: # the picture - role: identity modality: image source: { file: "preview.png" } facets: # what a query filters and re-ranks by file: ".metadata" rigged: { type: bool, from: { components: { contains: SkinnedModel } } } roughness: { type: number, filter: range, from: { file: "mat.yaml", field: "floats.roughness" } } ``` **Roles.** Each `data` and `content` entry has a `role`, and a query matches in two slots: - **`identity`**: what an asset is. For anything you look at, the picture; for anything else, the text that says what it is. - **`capability`**: what it does and how it is made. `interface` (the signatures or shape a caller uses) and `implementation` (the body) both count as capability, and a type with code usually declares both. Ask what a person would recognise an asset of the type by, and what it does, and point each role at the file that says it. For text, that is the asset's description: the file your template starts with a `[[describe]]` block, which the author writes or `services describe` fills in (see "Ask your assets to say what they are"). **`data`.** `extractor: verbatim` embeds a file's text as it is; `symbols` embeds the declared signatures of code. `source` is `{ file }` or `{ files: [...] }`. Never index a file name (`source: { field: name }`): one or two words carry nothing to match. **`content`.** `modality: image` embeds the picture itself, so a text query matches what the asset looks like. A type whose assets are looked at makes the picture its identity. **`facets`.** What a query narrows and re-ranks the matches by. `file` is embedded whole, so keys nobody declared in it are still found. Each further key is computed for every asset and states a value for every one, including `false`: a file can imply "not rigged" but never say it, and a query separates rigged from unrigged only because the unrigged ones say `rigged: false`. A key is `{ type: bool | number | enum, filter?: range, from }`, where `from` is `{ file, field }` (a field of one of the asset's files, dotted for nesting), `{ metadata: key }`, or `{ components: { contains | any_outside } }` (what the asset's entities carry). ## What blocks a push A push checks every asset it carries against its type. These refuse it: - a required file that is missing, a `content` check that fails, a `described` file not written yet; - an error from the type's `validate`. Unlisted files and warnings do not. A `described` file blocks only a push that changes the asset. When a push is refused, the message names each asset and what it lacks. `world.publishBlockers()` and `zm status` read the same list without pushing. ## Typing a result from the asset (`refShapes`) A `ref` method whose result depends on the asset (one entry per child folder, per row of a config, per control a map declares) can only be annotated as `{ [string]: Thing }`, which accepts any key. `refShapes` states the result for each asset instead: a function returning a Luau type expression for that asset, and the module whose types the expression uses. Read the asset; never run it. ```lua -- inputMap.assetType/behavior.luau M.refShapes = { activate = function(self): (string, string) local names = {} for _, control in ipairs(M.ref.controls(self)) do table.insert(names, control.name .. ": Handle") end if #names == 0 then return "", "" end return "{ " .. table.concat(names, ", ") .. " }", "@builtin::modules.zinput.scheme" end, } ``` With it, `map.jump:onPressed(fn)` is checked and `map.noexisting` is reported. A per-asset type applies where the call site names which asset: a component field whose default names it, or an annotation `AssetRef<"inputMap", "<identity>">`. `asset.resolve(name, category)` carries only the category, and a name computed at runtime carries nothing, so calls on those keep the declared return. The type belongs to the call's result: index it there, or bind what you need from it there, and the names stay checked. `require("@builtin::assetTypes.assetType.shared.refShapes").published()` shows what was published: `categories` (each type's method surface) and `returns` (per-asset results by identity, then method). An identity missing from `returns` was never published. Results are recomputed when an asset is written; at most 64 assets of one type are read. ## Putting an asset in a scene (`ref.instantiate`) A caller writes one piece of code against every instantiable type, so what `instantiate` returns is fixed: ```lua local Instantiable = require("@builtin::assetTypes.assetType.shared.instantiable") M.ref = { instantiate = function(self, target, opts) local root = Instantiable.root(self, target, opts) -- compose the asset under `root`, now return Instantiable.result(self, root, idMap) end, } ``` **In.** `target` is the entity the asset lands under, or onto for a hierarchy type; with none, the type spawns a new root. `position`, `rotation` (three numbers in degrees, or a quaternion), `scale`, `name` and `temporary` mean the same for every type: `Instantiable.root` applies them to a root you make, `Instantiable.place` to one you adopt. Document any options of your own in the hook's `--!arg` docs. **Out.** `(root, idMap)`. `root` is the composed root, live when you return: build synchronously, never defer to a component's `awake`. `idMap` maps each original id to the spawned one, so a component that composes the asset again on every load can pass it back in and keep references into the composition. Every call goes through `Instantiable.result`, which refuses a root that is not live and turns a missing `idMap` into `{}`. ## Inspecting an asset (`ref.inspect`) `asset.inspect(ref)` builds a record every asset shares (`identity`, `name`, `guid`, `source`, `typeName`, `typeDefinitionPath`, `scope`, `origin`, `description`, `tags`), then calls `ref.inspect(self)` for the type's own `detail`: ```lua M.ref = { inspect = function(self) -- read the asset's own files, never runtime state: inspect works on an asset -- that has not been compiled, uploaded or registered return { --[[ what makes this asset what it is ]] } end, } ``` Without it, the record is the shared part alone, and an agent inspecting the asset learns nothing of what it is. A hook that raises leaves `detail` empty and sets `record.warning`. ## Discovery - `asset.list("assetType")`: every registered type. - `asset.inspect("<typename>")`: the type, its README and its `about.yaml` texts. - `asset.resolve("<typename>", "assetType")`: the type itself.

# Component (asset type) A component is a reusable behavior + data unit attached to an entity. The component file declares public fields, methods, and lifecycle callbacks; the engine instantiates one per attachment and drives its hooks every frame. Components are the primary unit of gameplay code — movement, AI, animations, UI panels, network sync, and per-entity state all live here. ## When to use one - You need per-entity state that survives across frames. - You need per-entity behavior driven by engine lifecycle hooks (`start`, `update`, `onDestroy`). - You want to expose configurable fields to designers / `entity.spawn` callers / scenes without code changes. If you need a stateless pure-function library, use a `.module`. If you need to generate content declaratively, use a `.service`; compute work belongs in a `.computeShader`. ## Where it lives - Source: `/zero/source/.../<Name>.component/` - Identity: `<Name>` (the `.component` suffix strips from the identity, but the folder retains the suffix on disk). - Folder shape: - `init.luau` (or `init.lua`) — declares the component. **Required.** - `README.md` — instance-level documentation. **Required.** - `.metadata` — agent-editable tags + free-form fields. **Required.** The structural contract is enforced by `asset.validate` against this type's `type.yaml`. ## How to create one Always start with the scaffold — it guarantees the folder shape matches `type.yaml` from the moment it's on disk: ```luau asset.create("component", "<Name>") -- Creates: /zero/source/<Name>.component/ -- init.luau (canonical declare + public block + hooks stubbed) -- README.md (instance README template) ``` After scaffolding, edit `init.luau` to fill in the actual fields and behaviour. The component registers as soon as the file is written — hot-reload is automatic; no engine restart required. ## How it operates 1. **Registration.** Writing `init.luau` into a `.component/` folder indexes the asset, mints a guid (in the `.meta` sidecar), and surfaces the type to the engine's component registry. Same-frame visible to `entity.component.add`. 2. **Attachment.** `entity(id).component.add(name, data)` (or the batch form `tools.use("entityOps", "addComponents", targets, { [name] = data })`) attaches an instance. The `data` table's fields override the component's declared defaults; omitted fields take the declared default. The `data` values are copied into `public.*` BEFORE `awake()` runs. 3. **Lifecycle.** The hooks run in this order: - `awake()` — same frame as attach, immediately after the data copy. Initialise state, set up native bridges, register with other systems. Other components on the same entity may not have awoken yet. - `start()` — the next frame. Every component on the entity has completed `awake()` by then, so cross-component setup is safe here. - `update(dt)` — same frame as `start()`, then every frame after, for as long as the gameplay clock is running. `fixedUpdate(dt)` runs once per physics step, straight after it, with the step's `dt`, so a frame can run it several times or not at all; `editorUpdate(dt)` runs while the clock is held. Which of them ticks is decided by `engine.mode` AND `engine.paused` together — see **Per-frame hooks and the two axes** below, and `man modes`. - `onDestroy()` — when the component is removed via `component.remove` or when the owning entity is despawned. Release resources, drop native ECS components. For the full list (`onEnable`, `onDisable`, `fixedUpdate`, `editorUpdate`, `onPropertyChanged`, `onAssetReload`, `onModuleReload`, `onBeforeSave`, …) and the timing details, **read `man components` — that is the canonical lifecycle reference. Generic component patterns (declare blocks, public fields, sync, ECS bindings, typed methods) all live there.** 4. **Public surface.** Fields declared in `public` are inspectable, editable in the inspector, and persist with the entity. Methods are declared on that same table with a colon — `typed function public:method(args)` — and every one of them takes the component ref as `self`, so a caller invokes it with a colon too: `entity(id).component.get(name):method(args)`. That is the one calling convention a component ref answers to: the reflection methods `ref:fields()` / `ref:getField(name)` / `ref:setField(name, value)` take the same spelling. A function the chunk declares at file scope (`function helper()`) is the component's own, reachable from its hooks under its bare name; `public` is what the ref carries. 5. **Settings and the Inspector card.** `type.yaml` names the component's settings schema as `settings: { schema: { instance: "init.luau", export: "public" } }`: the `public` table IS the schema, and its values live on each entity the component is on, so `asset.schema(componentRef)` answers the Field descriptors and no values file exists. On an entity the Inspector shows the component as a card whose generic `settings` section edits those fields as typed controls, each edit checked against the schema and written to the live component as one undoable operation. `type.yaml` also names `inspector: { instance: "inspector.luau" }`: a component that ships an `inspector.luau` beside its `init.luau` shapes its card — the file returns `{ sections, replace, order }` (see `assetTypes/README.md`, "`inspector:`"), each section's `build(ctx)` reading `ctx.component` (the live component) and `ctx.selection.id` (the entity). `SceneModule.component/inspector.luau` replaces `settings` with the bound module's declared inputs. 6. **Events.** An `events` block declares typed moments the component fires from inside — `events = { onHit = Event({ dmg = Field.number(0, NoSync) }) }`. The owner fires with `events.onHit:fire({ dmg = 10 })`; outside code subscribes through the proxy's subscribe-only facade, `entity(id).component.get(name).events.onHit:connect(fn)` (`:once` / `:wait` too). Pass `Sync` as the event's second argument to replicate a fire to other peers. Events let one component react to another's moments without polling. Full reference: **`man components`**, Events section. 7. **Hot reload.** Editing `init.luau` reloads the component definition; live instances are reconciled with the new declaration in-place, and each crosses one lifecycle boundary: `onDestroy()` ends the running life, then `awake()` and `start()` construct the one that replaces it, and `update()` resumes on the next frame. `public` and `private` values carry across; module-level `local`s belong to the chunk, so the new life starts with them at their initial values and its `awake`/`start` are what fill them in. Whatever the old life handed elsewhere — a subscription, a shared registration, a spawned entity — is released in `onDestroy`, the call that pairs with the construction about to run. An edit that leaves the source byte-identical crosses no boundary at all. A field carries its value across when something stated it: a key of the `data` table the instance was attached with (a scene record's data is that table), or a write made since. Every other field takes the edited source's declared default, so changing a default reaches every instance that left the field to it. An instance that states its own value for a field whose default the edit changed keeps that value, and the reload logs a `[HotReload]` warning naming the field, the entity, the value kept and both defaults. ## Discovery - `asset.list("component")` — every registered component (engine + world + libraries). - `asset.inspect("<name>")` — identity, scope, public fields, lifecycle methods, source path, and this type README. `detail` carries the component's declared `fields`, `methods`, and `events`, parsed from its source — `tools.use("assets","describe", "<name>")` renders it as markdown, so a component's events are visible without opening its source. - `ls /zero/source/<Name>.component` lists the files the folder holds. - `entity(id).component.list()` — components attached to an entity. ## Per-frame hooks and the two axes `engine.mode` (`"edit"` / `"play"`) and `engine.paused` (the gameplay clock) are independent, and the per-frame hooks read them separately: - `update(dt)` / `fixedUpdate(dt)` tick while **the gameplay clock is running** — whichever mode the engine is in. - `editorUpdate(dt)` ticks while **the clock is held** — because the mode is `edit`, or because play is paused — and also alongside `update` whenever edit is running. Which gives four states, and this table is the contract: | `engine.mode` | `engine.paused` | hooks that tick | |---|---|---| | `edit` | `true` | `editorUpdate` | | `edit` | `false` | `update`, `fixedUpdate`, `editorUpdate` | | `play` | `false` | `update`, `fixedUpdate` | | `play` | `true` | `editorUpdate` | Entering edit sets `paused = true` and entering play sets it back to `false`, so a session that never writes `engine.paused` only ever sees rows 1 and 3 — which is where the shorthand "`update` is the play tick, `editorUpdate` is the edit tick" comes from. It is the two default rows of a four-row table, not the rule. **Row 2 is the one that surprises.** With `engine.paused = false` in edit — set by hand, or by a tool that advances the gameplay clock to sample it, such as a `capture.collage` given a `duration` — `update` and `editorUpdate` both fire, once each, every frame. A component that declares both and routes them to one body therefore runs that body **twice per frame**: ```luau local function drive(dt) ... end function update(dt) drive(dt) end function editorUpdate(dt) drive(dt) end -- twice per frame in row 2 ``` Nothing reports the doubling; it reads as an animation running at twice its intended speed. To get exactly one tick per frame in every row, ask which axis you meant and answer it in the body: ```luau function update(dt) drive(dt) end function editorUpdate(dt) if engine.paused then drive(dt) end end ``` A scene `entrypoint.luau` declaring the same two hook names is dispatched by the scene loader, not by this table: there `update` needs play AND running, `editorUpdate` needs edit, and play-paused ticks neither. Read `man scenes` before carrying a component's rule to an entrypoint. ## Authoring conventions - Annotate public fields with `--!desc` so the inspector + LSP show documentation alongside the field name. - Declare lifecycle hooks (`start`, `update`, `onDestroy`) explicitly rather than relying on engine defaults — readers can see at a glance what runs when. - Keep `update(dt)` cheap — it runs every frame per instance. Move heavy work to `start`, to a `.computeShader`, or behind a job (`man jobs`). - For multi-entity batching, prefer `tools.use("entityOps", "addComponents", targets, components)` over a loop of `entity(id).component.add` — it takes many targets and many components in one call. ## Common pitfalls - **Naming.** The component identity is the folder stem with `.component` stripped (e.g. `<Spinner>.component/` → identity `Spinner`). Don't repeat the suffix in the identity passed to `component.add`. - **`init.lua` vs `init.luau`.** Either is accepted (it's a `one_of_group: "entrypoint"`), but `.luau` is canonical. Mixing both in one folder is invalid. - **`update` in edit mode.** It runs whenever the gameplay clock is running, and entering edit stops that clock — so `update` is idle in a freshly-entered edit session and ticks again the moment anything sets `engine.paused = false`. Use `tools.use("wld", "play")` to test update logic under the mode it ships in; `tools.use("wld", "edit")` to return. See **Per-frame hooks and the two axes** above. - **Renaming.** Renaming the folder changes the identity. References to the component are recorded against the component itself, so renaming or moving it does not break them. ## Related types - `.module` — pure-function library, no per-entity state. - `.service`: a declarative content generator, no per-entity state. - `.preset` — a captured component configuration, replayable into `component.add` without re-typing fields. - `.bundle` — entity hierarchies that may carry component attachments as part of the bundle. ## In the Inspector Fields: its execution order, hooks, and how many methods and events it declares, then the fields its `public` table declares as read-only typed controls holding their defaults, with **Check** and **Open** for its entry file. Instances: a link to every entity carrying it. What its card shows on an entity comes from the component's own `inspector.luau`.

# pathNetwork Path networks built at runtime from Luau: roads and streets, race tracks, railway and tram lines, footpaths, river courses, patrol, delivery and tower-defence routes. A network is **nodes** (places, junctions, ends) joined by **edges** (paths through control points). Each edge carries directed **lanes**. `build` turns the network into drivable surfaces with static colliders and a material, conforms the terrain under them (cut and fill, not floating or buried), and joins the lanes into a graph that answers the nearest lane to a point, a route between two places, and the point a set distance ahead: what AI drivers, traffic, trains and followers steer by. Editing a node or an edge and building again rebuilds the surfaces and the ground that edit reaches (the edges at the node, their junctions, the ground under them) and leaves the rest standing, so an edit costs what it reaches; the lane graph is joined again in one pass over its lanes. The same calls build it on native and in the browser. ```luau local paths = require("@builtin::modules.pathNetwork") local net = paths.new({ lanes = { forward = 1, backward = 1 }, speedLimit = 15 }) local a = net:addNode({ 0, 0, 0 }) local b = net:addNode({ 200, 0, 40 }) local c = net:addNode({ 380, 0, -60 }) local d = net:addNode({ 180, 0, -220 }) net:addEdge(a, b, { points = { { 100, 0, 40 } } }) net:addEdge(b, c) net:addEdge(b, d, { lanes = { forward = 2, backward = 2 } }) -- b is now a junction net:addEdge(c, d, { bank = 6 }) print(net:build()) -- { edges, junctions, texels, triangles, lanes, ms } -- Live edit: only the edges at `c` and the junctions at their ends rebuild. net:moveNode(c, { 400, 0, -40 }) net:build() ``` ## Settings `paths.new(opts)` states network-wide settings; `addEdge(a, b, fields)` and `setEdge(id, fields)` state them per edge. An edge reads its own, then the network's, then `paths.DEFAULTS`. | Setting | Default | | |---|---|---| | `lanes` | `{ forward = 1, backward = 1 }` | Lanes from the first node to the last (`forward`) and back. `backward = 0` is one-way. | | `laneWidth` | `3.5` | Metres per lane. | | `shoulder` | `0.5` | Metres of surface beyond the outer lanes, each side. | | `width` | from the lanes | The whole surface's width; when stated, the lanes share it. | | `speedLimit` | `13.9` | Metres per second; `route { by = "time" }` reads it. | | `bank` | `0` | Degrees the surface tips about its heading (positive lowers the right edge): one number, or one per control point, ends included. | | `elevation` | `"terrain"` | `"terrain"` lays the surface on the ground; `"points"` takes the control points' heights (a bridge, a ramp, a raised track). | | `smoothing` | `16` | Metres the ground-following profile is averaged over. | | `lift` | `0` | Metres the surface stands above the ground it follows. | | `conform` | `true` | Cut and fill the ground to meet the surface. A bridge sets `false`. | | `bed` | `0.06` | Metres the ground sits below the surface. | | `falloff` | `8` | Metres over which the ground blends back to its own height. | | `skirt` | `0.8` | Metres the side walls reach down. | | `resolution` | `2` | Metres between cross-sections. | | `uvScale` | the width | Metres of surface one texture repeat covers along the path. | | `material` | `@builtin::materials.default` | What the surface is drawn with. | | `tint` | dark grey | `{ r, g, b }` over the material; `nil` keeps its own colour. | | `collider` | `{ friction = 1.0 }` | Fields for each surface's `MeshCollider` (`friction`, `restitution`, and any other field it takes); `false` for none. | Network-only: `name` (the parent entity), `drive` (`"right"` or `"left"`: which side forward lanes keep to), `terrain` (a Terrain entity or a list, `false` for none; unset uses every Terrain in the scene), `parent` (an entity the surfaces go under). ## Authoring | Call | | |---|---| | `net:addNode(pos, { id?, elevation?, junctionRadius? })` | A node; answers its id. | | `net:addEdge(a, b, { points?, id?, ...settings })` | An edge through `points` from `a` to `b`; answers its id. | | `net:moveNode(id, pos)` / `net:setNode(id, fields)` | Move or change a node. | | `net:setEdge(id, { points?, ...settings, clear? })` | Change an edge; `clear` lists settings to drop. | | `net:removeEdge(id)` / `net:removeNode(id)` | Remove; the ground comes back on the next build. | | `net:addPlan(plan, edgeFields?)` / `paths.fromPlan(plan, opts?)` | Add a laid-out plan (below). | | `net:spec()` / `net:apply(spec)` | The network as plain data, and bringing it to a spec (by id, changing only what differs). | | `net:build({ all? })` | Build what changed; answers `{ edges, junctions, texels, triangles, lanes, ms }`. | | `net:destroy()` | Take the surfaces down and give the ground back; the nodes and edges stay. | A node where three or more edges meet becomes a **junction**: the edges stop short of it and a junction surface joins their ends, sharing their vertices. On the ground the junction lies on a plane through the node that keeps the grade of its through way (the two edges that run most nearly straight on into each other) and is level across it; the other edges tip onto that plane where they arrive and curve onto its grade along the way they arrive, so a road through a junction on a slope keeps its grade and a side road climbing to it eases onto it the way it meets a real one. Across a node of two edges the edges share one tangent and, on the ground, one height and grade, so the surface runs on without a step or a crease. Where an edge eases from its own grade to the one it meets, its grade changes by at most 1.5 % per metre over any edge long enough to hold the curve. ## Procedural layout `paths.procedural` answers plans (`{ nodes, edges }`) that `paths.fromPlan` or `net:addPlan` builds. The same seed lays out the same network. | Rule | | |---|---| | `connect(places, { loops?, meander?, spacing?, seed? })` | Join a set of places: a spanning tree plus `loops` extra links that cross nothing. | | `grid({ cols?, rows?, spacing?, origin?, jitter?, seed? })` | A grid of streets. | | `circuit({ origin?, radius?, radiusZ?, count?, wander?, pointsPerEdge?, seed? })` | A closed circuit round an ellipse; `wander` is the share of the radius it wanders by (0 to 0.9). | ## Queries | Call | | |---|---| | `net:nearest(pos, { heading?, maxDistance?, lanes? })` | The nearest edge, distance along it (`s`), lateral `offset`, `onSurface`, and the lane there with `laneDistance`, `lanePosition`, `direction`. `lanes` (a route's `lanes`) looks only at those, so a driver keeps to its route through a junction. | | `net:route(from, to, { by? })` | Lanes in order, `length`, `cost`, and `points` to follow. `from`/`to` are points or `{ lane, distance }`; `by = "time"` takes speed limits into account. | | `net:lookAhead(from, metres, { route?, choose? })` | The point that far ahead along the lanes, through the nodes. | | `net:lanePath(ids, { closed? })` | The polyline of a run of lanes, for a loop or a racing line. | | `net:lanePoint(lane, d)` | Position and direction a distance along a lane. | | `net:sample(edge, s)` | The built surface's position, forward, right, up and bank at `s`. | | `net:lane(id)` / `net:laneIds()` | A lane: edge, direction, index, offset, width, speed limit, length, `next`, `prev`, `stopLine`. | | `net:node(id)` / `net:edge(id)` / `net:nodeIds()` / `net:edgeIds()` | The network as data. | | `net:groundHeight(x, z)` | The ground's height now, cut and fill included. | | `net:entity()` | The entity the surfaces stand under. | Lane ids read `<edge>:+<n>` (running from the edge's first node) and `<edge>:-<n>` (toward it); `n` counts out from the centreline. A lane arriving at a junction carries a `stopLine`. `next` lists the lanes it leads on to: at a junction, one per other edge; at the end of a single edge, the lanes back. ## Followers and drivers The `PathFollower` component moves an entity along `route.points` or a lane loop at a constant speed. A physics vehicle (`VehicleController` with `controlSource = "script"`) drives a network by steering toward `net:lookAhead({ lane, distance }, metres)` from `net:nearest(position)`. ## Notes - The surfaces are spawned as temporary entities and the ground edits live in the loaded terrain: a network is built from Luau when the scene runs (a scene script, a component's `awake`), and `net:spec()` is what to store. - A built network keeps to its ground: when a Terrain under it loads after the build, or is read again from its asset (a re-bake, `reload`), the network builds itself again on it. - Surfaces are in world space; the parent entity stands at the origin. - Sub-modules: `paths.geometry` (centrelines, cross-sections, meshes), `paths.lanes` (the lane graph), `paths.procedural` (layout rules).

# luau_introspect (module) Parses Luau/asset source TEXT into structured declarations. Pure string/pattern parsing (`string.find` / `string.match` / `string.gmatch`) over the literal source — no compiling, no VM spawn, no runtime state, no engine FFI. Given source text, it extracts what is written in the file. This is the shared parser every per-assetType `M.ref.inspect` hook uses to turn a component/module/tool's own source into the structured record `asset.inspect` returns. ## Exports - `docstrings(src) -> DocMap` — scans `--!desc` / `--!arg` / `--!return` / `--!example` comment runs and binds each run to the name of the declaration on the next non-comment line (the identifier after `function`, `public:`, `local function`, or `M.`). - `publicFields(src) -> { FieldEntry }` — parses `public = { name = Field.<kind>(default, mode), ... }` table-literal entries and module-scope `public.<name> = Field.<kind>(...)` assignments. - `events(src) -> { EventEntry }` — parses `events = { name = Event(payloadSchema?, syncMode?), ... }` table-literal entries. - `methods(src) -> { MethodEntry }` — parses `function public:<name>(...)` / `typed function public:<name>(...)` declarations (params + optional return type). - `lifecycleHooks(src, catalog) -> { string }` — top-level `function <name>(` declarations whose name is in the caller-supplied `catalog` array. - `moduleExports(src) -> { ExportEntry }` — parses `M.<name> = function` assignments, `function M.<name>(...)` declarations, and a trailing `return { foo = foo, ... }` export table. - `forSource(src, computeFn) -> any` — memoises `computeFn(src)` keyed on `src` itself in a module-local table. The same source text returns the cached result without re-running `computeFn`; different source text recomputes. Keyed on the source content (not an asset checksum) because composite/container assets (component folders, scene folders, etc.) all hash to the empty-string checksum — a checksum-keyed cache collapses every such asset's detail onto whichever one was inspected first. ## Usage ```luau local Introspect = require("modules.luau_introspect") local src = self:getInitScript() local detail = Introspect.forSource(src, function(s) return { fields = Introspect.publicFields(s), events = Introspect.events(s), methods = Introspect.methods(s), hooks = Introspect.lifecycleHooks(s, lifecycleCatalog), } end) ``` ## Notes - Every function is a pure string→table transform: same source text in, same structured table out, every time. No reads of live component state, no entity/world queries. - Structural scanning runs over a comment- and string-aware **mask** of the source (a same-length copy where comment bodies and string-literal contents are blanked to spaces, delimiters and newlines preserved). Pattern matches and brace/paren balancing run on the mask — so a brace, `Field.`, `Event(`, or a whole entry that appears inside a comment or a string literal never registers — while captured values are sliced from the original source at the same (aligned) indices. This makes the parser robust to apostrophes in comments, commented-out entries, string defaults containing `}` / `Field.` / `Event(`, and `[[ ]]` long strings. - `default` / `category` are raw trimmed source-text slices (with any trailing comment stripped), not evaluated values. - For a **ref constructor** (`Field.assetRef` / `dataRef` / `resource` / `componentRef`) the FIRST positional argument is the category / contract / componentType selector, captured under `category`; the SECOND argument is captured under `default`. - For every **other** Field kind the first argument is the `default` and `category` is nil. - A trailing `Sync` / `NoSync` identifier is captured as `sync`, tolerating a trailing comma or a trailing comment after the last argument. - Field/Event entries whose key is a computed or indirect expression (`[expr] = Field.number(...)`) are omitted — only literal identifier keys are recognised. - `methods` captures a `...` variadic parameter (as `name = "..."`), with its `: <type>` annotation when present. - A `--!desc` written above a field/event declaration (`<name> = Field.<kind>(...)` / `<name> = Event(...)`) or a `public.<name> =` assignment binds to that name in `docstrings`, and is folded into the corresponding `publicFields` / `events` entry's `desc`. - `lifecycleHooks` never hardcodes the lifecycle-callback catalog; the caller passes the list of names to match against. - `forSource`'s memo is bounded (oldest-key eviction) so a long session touching many distinct asset versions can't grow it without limit.

# assetType.shared.ref Builds the metatable every `AssetRef` (the `{ __ref, type, name, guid, identity, path }` envelope returned by `asset.resolve` / `asset.ref`) carries. Replaces the per-call C metatable that used to live in `crates/zero_scripting/src/ffi/bindings/asset.rs::attach_asset_ref_metatable`. ## Public API ```lua local assetRef = require("@builtin::assetTypes.assetType.shared.ref") -- Called by the Rust factory (push_asset_ref_handle) via -- _G.__build_asset_ref_proxy after the envelope fields are set. assetRef.build(envelope) -- attaches AssetRefMT, returns the table ``` The module exposes no invalidation surface — discovery is registry-driven and hot-reload is transparent (see "Discovery and hot-reload" below). ## Method dispatch order `ref.foo` is resolved in this order: 1. **Default methods** — `getSource` / `getBytes` / `getText` / `exists` / `inspect` and the lazy `meta` property. Per-type definitions cannot override these (engine contract from gh#1889). 2. **Per-type `ref` table** — discovered through `asset.resolve(<typename>, "assetType")` + `require(<identity>.behavior)`. The lookup resolves to whichever `<typename>.assetType/` folder is currently registered for the typename (built-in, user, or library-vendored) and pulls its `ref` methods. 3. **Nil** — unknown key, same shape as the original C metatable. ## Adding methods for a new asset type Drop a `behavior.luau` into the type folder: ``` src/lua/lib/assetTypes/<typename>.assetType/ ├── type.yaml -- structural spec (existing) ├── behavior.luau -- ref + global behaviour (new) └── template/ -- placeholder body (existing) ``` `behavior.luau` returns: ```lua return { ref = { --!desc Per-instance method on every `<typename>` AssetRef. myMethod = function(self, ...) ... end, }, global = { -- Reserved for the asset.<typename>.* surface — not consumed -- yet; included so the contract from gh#1889 lands cleanly. }, } ``` Within `ref` methods, `self` is the AssetRef envelope: `self.path`, `self.identity`, `self.guid`, `self.type`, `self.name` are available. Engine-required fields (`guid`, `path`, `identity`, `type`) must not be redefined. ## Discovery and hot-reload Type discovery uses the asset registry, so it doesn't matter where a `<typename>.assetType/` folder lives — engine built-ins under `@builtin::assetTypes.<X>`, user types dropped under `/zero/source/<X>.assetType/`, or types vendored inside an imported library all resolve identically. The dispatcher walks `asset.resolve(<typename>, "assetType")` → canonical identity → `require <identity>.behavior` on every miss; the asset registry is the cache for the resolve half and Luau's `_LOADED` is the cache for the require half. Hot-reload is transparent. When a `<typename>.assetType/behavior.luau` is rewritten through VFS, the engine's `invalidate_require_cache_for_state` re-runs the module and mutates the cached `_LOADED[<identity>.behavior]` table in place. Dispatch reads `mod.ref` on every access (rather than caching a sub-pointer), so existing AssetRefs see the new methods on the very next access — no Rust-side hook into this module is needed, and no invalidation API is exposed for callers to call. The same registry-driven path also handles type **registration** correctness: dropping a new `<typename>.assetType/behavior.luau` updates the asset registry, the next `asset.resolve(<typename>, "assetType")` returns the new ref, and AssetRefs of that type immediately gain the new methods. ## Why Luau, not Rust The asset surface needed per-category behaviour (`material:getProperties()`, `bundle:instantiate(entityId)`, `tool:run(args)`) and the old shape couldn't grow without an FFI change per method. Owning the proxy in Luau means: - Type-specific methods ship as content (the `<typename>.assetType/` folder), not engine code. - Adding a new asset type drops in a new folder; no Rust rebuild. - Methods can call any other Luau global (`vfs`, `asset`, `Material`, `entity`, etc.) directly, instead of going through narrow FFI primitives. ## Consumers - `crates/zero_scripting/src/ffi/bindings/asset.rs::attach_asset_ref_metatable` — the Rust factory that pushes envelopes invokes `_G.__build_asset_ref_proxy` once per push. - Every Luau call site of `asset.resolve` / `asset.ref` / `entity(id).component.X.material` / any binding declared `AssetRef<...>` — they all receive envelopes built through this module.

# yaml.module YAML decode + encode for authored engine content. Pure Luau, no engine dependencies — a general parsing library, not data-system plumbing. ```luau local Yaml = require("@builtin::modules.yaml") local doc = Yaml.decode(vfs.read(path)) vfs.write(path, Yaml.encode(doc)) ``` ## Supported subset - Block mappings (`key: value`) and block sequences (`- item`), nested to any depth. - Compact sequence-of-mapping entries (`- path: x` / ` kind: y`). - Flow collections — `{ a: 1, b: 2 }` and `[1, 2, 3]` — single line. - Plain scalars with type inference: `~` / `null` → nil, `true` / `false` → boolean, numeric literals → number, everything else → string. - Single- and double-quoted strings (`''` escapes a literal quote inside a single-quoted string; `\n` `\t` `\r` `\\` `\"` inside a double-quoted one). A quote opens a quoted scalar where a scalar begins — after `key:`, after a `- ` entry marker, or inside a flow collection — so a plain scalar carries an apostrophe as data (`note: the world's rules`). Quoted keys are read in flow mappings. - `#` comments — honored outside quotes, so a `#` inside a quoted string is kept as data. - Literal (`|`) and folded (`>`) block scalars, with a chomping indicator (`-` strips the final newline, `+` keeps every trailing blank line, none keeps one newline) and an indentation indicator (`1`-`9`: the content's indent past the parent's), in either order (`|-`, `>+`, `|2`, `>1-`). A block scalar's content is literal text: quotes (balanced or not), `#`, `key: value` and `---` inside it are data. - An optional leading `---` document marker. ## Loud-error contract Constructs outside the subset above raise instead of misparsing: anchors/aliases (`&`, `*`), tags (`!`), directives (`%`), multi-document streams (a second `---`), a block-scalar header it cannot read (`|x`, `|-+`, `|0`), tab indentation, and inconsistent indentation (both block structure and block-scalar bodies). Every error carries the offending line number (`yaml: line N: ...`), so a bad config points straight at the line to fix. Tab indentation is rejected everywhere — including block-scalar body lines whose leading whitespace contains a tab. A tab after the first non-space character of a line is content and passes through. ## API - `Yaml.decode(text: string): any` — decode a YAML document into a Luau value (table, scalar, or nil for an empty document). Raises on malformed input or an unsupported construct. - `Yaml.decodeWithComments(text: string): (any, boolean)` — decode as `decode` does, and report whether the text carries a comment by the decoder's own rule: a `#` at a line's start or after whitespace, outside a quoted scalar and outside a block scalar. Re-encoding the value drops such comments, so an editor that writes a document back reads this first. - `Yaml.encode(value: table): string` — encode a Luau table as YAML (block style, two-space indent, alphabetically sorted keys). Raises on values YAML can't represent (functions, userdata, non-string mapping keys). A top-level empty table encodes to an empty document, which decodes back to `nil` (the YAML empty-document ambiguity).

# json JSON encode/decode library for Luau. Encodes Lua values to JSON strings and decodes JSON strings back to Lua values. Used for communication with the Rust side of the engine, the VFS read/write bridge, and any wire-format that needs JSON. Pure Luau, no engine dependencies. Compact and pretty-printed encoders, plus a hand-rolled decoder that streams the input by position so it works under WASM as well as native. ## Exports - `Json.encode(value: any, indent?: string, currentIndent?: string) -> string` — compact encode. Functions / unknown types and NaN/Inf encode as `null`. - `Json.encodePretty(value: any, indentStr?: string) -> string` — pretty-printed encode with sorted object keys (diff-friendly). - `Json.encodeArgs(...: any) -> string` — encode varargs as a JSON array. - `Json.decode(str: string) -> any` — decode a JSON string. Returns the decoded value, or `nil` + error message on failure. ## Usage ```luau local Json = require("@builtin::modules.json") local widget = { type = "button", text = "Click Me" } local compact = Json.encode(widget) -- '{"text":"Click Me","type":"button"}' local pretty = Json.encodePretty(widget, " ") local decoded = Json.decode(compact) local v, err = Json.decode("oops") -- v = nil, err = error message ``` ## Notes - Object keys are sorted alphabetically in both encoders for consistent output across runs. - Numeric keys on objects are stringified at encode time (JSON has no numeric keys). Pure-integer key sets get detected as arrays via `isArray` and encoded with brackets. - NaN, +Inf, -Inf encode as `null` — JSON has no representation. Round trips through `decode` recover `null` (Lua `nil`), so they don't preserve. - Unicode `\uXXXX` escapes decode to UTF-8 by hand to stay WASM-safe. Only the BMP is covered; supplementary planes via surrogate pairs are not. - Functions encode as `null`. - Decode is character-streamed — no regex, no `string.match` patterns on the whole input — so the line-and-column information needs to be reconstructed from the position offset.

# assetType runtime The machinery that reads a `<typename>.assetType/behavior.luau` and turns its declarations into live behaviour. A `behavior.luau` is a table of declarations — `ref` methods, `modules` shared code, an `events` schema, a `namePattern`, `refShapes`, and the `onCreate` / `onRegister` / `onChange` / `onDelete` / `validate` / `settingsDefaults` / `settingsCorrections` hooks. None of it runs itself. This is the code that runs it, and it lives here because reading a type's declarations is the **assetType type's own behaviour** — the same way `material.assetType` owns what a `.material` does. ## Sub-modules | Module | Reads | Responsibility | |---|---|---| | `ref.module` | `ref`, `modules` | Builds every `AssetRef` envelope, attaches the shared metatable, and dispatches per-type methods and shared modules onto it. Also owns edit-mode write-behind persistence. | | `create.module` | `onCreate`, `namePattern`, `validate` | Backs `asset.create`: resolves the type, checks the name against its pattern, runs `onCreate` (or clones `template/`), and writes the instance. `validate.module` beside it checks a creation `opts` table against the type's `createSchema`. Before running `onCreate`, resolves the type's settings chain (below) and hands the result to the hook as `opts.settings`. | | `settings.module` | `settings`, `settingsDefaults`, `settingsCorrections` | A type's declared settings schema and where its values live (`type.yaml`'s `settings:` block). `Settings.resolveForCreate` layers the schema's own defaults, the type's own `settingsDefaults(name, opts, asked)` hook (a DEFAULT the schema can't express — a name-derived convention, a fact read off a payload the caller handed it, a value following a field `asked` shows a higher layer naming; any later layer overrides it), the Preset Manager, an importer's settings, the caller's `settings` table, then the type's own `settingsCorrections(values, name, opts)` hook (a CROSS-FIELD CONSTRAINT the schema can't express, applied last over the fully merged values). A correction over a default/preset/importer value lands silently; a correction that would override what the caller's own `settings` table explicitly asked for refuses the creation instead, naming the field and why. Neither hook is ever handed a table to mutate; each returns what it wants changed (`settingsCorrections` may also return a `{ [field]: reason }` table for that refusal message). `Settings.cloneValues` deep-copies a values table — `create.module` hands `onCreate` a copy, never the table it stamps. `Settings.valuesOf` / `writeValues` read and write an asset's own values file. | | `typeYaml.module` | `type.yaml` | The folder a type lives in and its parsed `type.yaml`, decoded once per content version of the file. `settings.module` and `inspector.module` read their blocks through it. `about` / `aboutAt` read a type's `about.yaml` (`intent`, `function`, `usage`), leaving out any key that is empty or still starts with `[[describe]]`; `aboutRows` and `aboutMarkdown` lay the texts out for the Inspector and the `types/<name>` guide. | | `inspector.module` | `type.yaml`'s `inspector:` block | Which inspector a type declares for its assets (`inspector: { type: ... }` or `{ instance: ... }`), and the declaration that file returns — the sections it adds, the generic ones it replaces, and their order — or the problem that kept it from loading. | | `onRegister.module` | `onRegister` | Fires an instance's once-only registration hook — on arrival, on world load, and for `@builtin` library instances. | | `changeDispatch.module` | `onChange`, `onDelete`, `refShapes` | Routes a VFS source write or a folder delete to the enclosing typed asset's type hooks. | | `refShapes.module` | `refShapes`, `ref` | Publishes what every `AssetRef<category>` answers to, so a member read on an asset-typed value is checked against that category's real surface. | | `events.module` | `events` | The per-asset event runtime behind `ref.events`. | | `instantiable.module` | `ref.instantiate` | The instantiation contract an asset type opts into: `root` stands the root entity, `place` applies the base placement opts to one the type adopted, and `result` shapes the `(root, idMap)` every `instantiate` returns. Also registers the `sceneInstantiable` field-constraint validator. | | `declaration.module` | `type.yaml` | The type's decoded declaration, read once and held until a write inside an `.assetType` folder; what every question about a type as a whole reads. | | `previewRecipe.module` | `type.yaml` `preview:` | How an instance's `preview.png` is produced: which of the four recipes (`instantiate`, `image`, `surface`, `custom`) the type declares, and what that recipe needs. | ## Reaching it ```luau local rt = require("@builtin::assetTypes.assetType.shared") rt.ref.loadTypeBehavior("material") ``` Fields resolve lazily. The prelude requires the sub-modules directly, in dependency order (`ref`, then `changeDispatch`, `onRegister.install()`, `refShapes.install()`) — a table that required all six on load would take that ordering away from it.