# 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`, `destroy`). - You want to expose configurable fields to designers / `entity.spawn` callers / scenes without code changes. If you need a global service that outlives any entity, use a `.service` instead. If you need a stateless pure-function library, use a `.module`. ## 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 beside it on the fixed timestep; `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`, `destroy`) 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 service, 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. Update every `component.add(<oldname>, ...)` call and the scene JSON entries that reference it. ## Related types - `.module` — pure-function library, no per-entity state. - `.service` — globally-scoped behavior, 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`.

# `modules.particles` — Generic GPU-driven Particle System (deprecated) > **Deprecated.** This belongs to the earlier particle substrate. It stays loadable by identity and guid for content that already uses it; nothing new should use it, and search does not offer it. Particles are procgen sim nodes (`sim.spawn`, `sim.particles`, `sim.shader`) played through an effect: use `@builtin::assetTypes.effect`. A generic, GPU-driven particle substrate for VFX. Every active particle lives in a GPU storage buffer; physics runs entirely as a compute dispatch each frame; per-frame vertex output feeds the renderer directly via `renderer.mesh.create` — no CPU readback, no re-upload. Spawning happens on the CPU (cost bounded by the emission **rate**, not the active particle **count**) and writes new particle slots directly into the GPU state buffer. It is the substrate behind the `ParticleEmitter` component but works equally well as a script-side API for hand-rolled effects, custom WGSL update shaders, and per-particle scripted state. ## Quick start ```lua local particles = require("@builtin::deprecated.deprecatedParticles.engine") local NumberSequence = particles.NumberSequence local ColorSequence = particles.ColorSequence local fire = particles.create({ maxCount = 2000, rate = 120, -- particles/sec lifetime = { 0.8, 1.6 }, speed = { 1.5, 3.0 }, shape = { kind = "cone", size = {0.6, 1.2, 0.6}, partial = 0.4 }, gravity = { 0, 1.5, 0 }, -- buoyant drag = 0.4, size = NumberSequence.new({ { time = 0, value = 0.25 }, { time = 0.3, value = 0.7, envelope = 0.15 }, { time = 1, value = 0.0 }, }), color = ColorSequence.new({1, 0.9, 0.3}, {1, 0.2, 0.05}), transparency = NumberSequence.new(0, 1), blendMode = "additive", brightness = 2.0, }) -- Each frame, in your update tick: fire:setOrigin(torch.position.x, torch.position.y, torch.position.z) fire:update(dt) ``` For a declarative wrapper that lives on an entity, use the `DeprecatedSimpleParticleEmitter` component (`deprecated/deprecatedParticles.package/DeprecatedSimpleParticleEmitter.component`). ## Why GPU-driven | | CPU per-particle | GPU per-particle | |---|---|---| | 1 000 particles | OK | OK | | 10 000 particles | starts skipping frames | trivial | | 100 000 particles | impractical | trivial | | 1 000 000 particles | impossible | feasible on mid-tier GPU | | Custom physics | per-particle Lua call | one WGSL update shader | | Trail / mesh particles | extra CPU work | extra WGSL pass | The substrate also leapfrogs Roblox-class engines on the long list of features they can't offer in their CPU-only model: mesh particles, particle ↔ world collision, neighbour queries, custom force fields, curl noise. ## Architecture ### Storage buffers, per system Every system holds its particle state and its params. What it holds beyond that depends on how it draws. | Buffer | Size | Written by | Read by | |---|---|---|---| | `<id>_state` | `maxCount * 64 B` | CPU spawn, GPU update | GPU update | | `<id>_params` | 1556 floats (~6 KB) | CPU each frame + on change | GPU update | A **sprite** emitter builds a quad per particle: | Buffer | Size | Written by | Read by | |---|---|---|---| | `<id>_verts` | `maxCount * 4 * 92 B` (GPU vertex buffer, carrying the per-particle channel in its tangent words) | GPU update | renderer, and the material's fragment stage | | `<id>_indices` | `maxCount * 6 * 4 B` (GPU index buffer) | CPU once at create | renderer | The vertex + index buffers are created with `vertex=true`/`index=true` flags so `renderer.mesh.create` can wrap them as a renderable mesh with zero CPU copy. The renderer binds the same GPU allocation the compute shader just wrote to. A **mesh** emitter uploads its source mesh once and draws it once per particle, so it holds a placement and a colour instead of geometry: | Buffer | Size | Written by | Read by | |---|---|---|---| | `<id>_xforms` | `maxCount * 64 B` (one column-major 4x4 per particle) | GPU update | renderer | | `<id>_instdata` | `maxCount * 64 B` (four `vec4` shader-data lanes per particle) | GPU update | the material's fragment stage | Those two buffers are what `renderer.mesh.drawInstanced` reads: the matrices place each copy, and the lanes arrive in the fragment stage as `input.shader_data[lane]`, which is how copies sharing one mesh and one material each keep their own colour. 100 000 cube particles (24 verts) hold 12.8 MB this way, against the 220 MB the same emitter would hold as replicated geometry. ### What one particle carries into its material A material a particle system draws with reads four numbers belonging to the particle covering the fragment — its `life` (normalised age, 0 → 1), its own `seed` in [0, 1] fixed for its whole life, the world-space `size` it is drawn at, and `alive`. Include the reader and take them off either emitter kind: ```wgsl #include "@builtin::deprecated.deprecatedParticles.particle_data" fn fragment(input: FragmentData) -> vec4<f32> { let p = particle_sprite_data(input); // particle_mesh_data for a mesh emitter let flicker = 0.6 + 0.4 * sin(input.time * 8.0 + p.seed * 6.2831); return vec4<f32>(input.vertex_color.rgb * flicker, input.vertex_color.a * (1.0 - p.life)); } ``` A sprite emitter carries the four in the four words of each vertex the render pipeline reads as the tangent, a mesh emitter in the instance lane beside its colour, and `particle_layout` declares the order both compute passes pack. The seed is what lets a population vary out of unison: it differs between the particles of one emitter and reproduces for the same particle at any age, so a noise phase or an atlas frame chosen from it holds still while that particle lives. `@builtin::deprecated.deprecatedParticles.fx.fx_noise` takes it as a phase or an offset. `renderer.instanceData` is the per-ENTITY channel: an emitter is one entity, so the lanes it sets there are shared by every particle the emitter draws. ### Per-particle state (16 f32 = 64 bytes) ``` [0..2] position (xyz) [3] age (seconds since spawn; >= lifetime means dead) [4..6] velocity (xyz) [7] lifetime (seconds) [8..10] tint rgb (per-particle multiplicative tint; default 1) [11] base size (sampled at spawn) [12] rotation (degrees, current) [13] rot speed (degrees/sec) [14] per-particle seed in [0, 1] (used for envelope sampling) [15] reserved / user data ``` ### Params buffer layout The first 32 floats are per-frame data; the next 32 are a user-controlled param block for custom WGSL update shaders; the next 4 × 49 floats are NumberSequence packs (size, transparency, squash, rotSpeed); the final 129 floats are the ColorSequence pack. See `init.luau`'s `PARAM_LAYOUT` for the canonical offsets and `particle_layout.shaderModule` for the matching WGSL constants. Past the ColorSequence pack come the collision header, the collider records, and the grid a bound world distance field covers. ### Frame loop ``` 1. CPU: spawn pending particles → writeBuffer on state buffer 2. CPU: pack per-frame uniforms → writeBuffer (first 32 floats only) on params 3. GPU: dispatch update shader → reads state, integrates, samples curves, and writes this particle's output: a sprite emitter's 4 vertices, or a mesh emitter's matrix + shader-data lanes; collapsed to nothing with area if dead 4. GPU: renderer draws the mesh — as an entity's model for a sprite emitter, as a population for a mesh emitter ``` Vertex buffer is rebuilt every frame from the latest particle state. Dead particles emit a zero-area quad that the rasterizer drops for sub-pixel cost. That quad sits on the particle's own position, and a slot that has never carried a particle holds the emitter's origin — the vertex buffer is part of the scene's geometry, so a pass that gathers it (a distance field, a bake, a BVH) covers an extent the emitter actually occupies. ## Curves: NumberSequence + ColorSequence ```lua -- constant NumberSequence.new(1.0) -- two-point lerp NumberSequence.new(0, 1) -- full keypoint table (up to 16 keypoints; envelope is ± range per keypoint) NumberSequence.new({ { time = 0, value = 0.0 }, { time = 0.3, value = 1.0, envelope = 0.2 }, { time = 1, value = 0.0 }, }) -- a number keypoint list also takes its entries written positionally NumberSequence.new({ { 0, 0.0 }, { 0.3, 1.0, 0.2 }, { 1, 0.0 } }) ColorSequence.new({ 1, 0.5, 0 }) -- constant ColorSequence.new({ 1, 0, 0 }, { 0, 0, 1 }) -- lerp ColorSequence.new({ { time = 0, value = { 1, 1, 1 }, envelope = { 0.1, 0.0, 0.1 } }, { time = 1, value = { 0, 0, 0 } }, }) -- a keypoint list also takes its entries written positionally, and a list of -- bare colours spreads its stops evenly across [0, 1] ColorSequence.new({ { 0, { 1, 1, 1 } }, { 1, { 0, 0, 0 } } }) ColorSequence.new({ { 1, 0.85, 0.35 }, { 1, 0.35, 0.05 } }) ``` Every field of a keypoint reaches the GPU pack as one float, so a time, value, channel or envelope that is not a number is refused by the constructor, naming the keypoint's index and the types it read. Both classes pack a fixed 16 stops: a longer list is resampled down to 16 keeping both endpoints, and the resample logs a warning naming the cap and how many stops it dropped. Sampling: ```lua seq:evaluate(t) -- deterministic seq:sample(t) -- envelope-randomized (math.random under the hood) seq:sample(t, seed) -- envelope-randomized with a specific seed ``` The GPU shader samples each curve per particle per frame using the per-particle seed stored at state slot 14, so envelope randomness is deterministic across frames for a given particle and runs with no per-frame CPU cost. ## Emission shapes ```lua shape = { kind = "cone", -- "point" / "box" / "sphere" / "cylinder" / "disc" / "cone" size = { x=1, y=1, z=1 }, style = "volume", -- "volume" | "surface" inOut = "outward", -- "outward" | "inward" | "inandout" partial = 0, -- shape-specific (hemisphere cap, annulus inner, taper) spreadAngle = 0, -- cone broadening around the sampled direction, degrees } ``` Sampling runs on the CPU at spawn time only — the cost is per emitted particle, not per active particle. Shapes are pure functions in `shapes.module/init.luau`. ## Collision An emitter meets things when `collision` names what a hit does — `"bounce"`, `"stop"` or `"kill"` — and its collider list says what it can hit: ```luau local sys = particles.create({ rate = 400, lifetime = 6, speed = 0, gravity = { 0, -9.81, 0 }, collision = "bounce", restitution = 0.3, friction = 0.4, colliders = { { kind = "world" }, -- the scene itself { kind = "sphere", position = { 0, 2, 0 }, radius = 1.5 }, }, }) ``` `plane`, `sphere` and `box` are shapes the emitter carries — eight at most, because they ride the params buffer the update shader already binds. `world` is the scene's own geometry: terrain, stairs, a rock, anything nobody described as a shape. It reads the distance field `sceneProxy` builds — the same coarse volumetric stand-in long-range lighting queries use — so contact costs one texture read wherever a particle happens to be, on- or off-screen. The first emitter to ask for one builds it (`worldResolution` voxels per axis, 64 by default); after the scene changes, `sceneProxy.refresh()` rebuilds it and the emitter picks the new grid up on its next update. Two things follow from the field being coarse: contact lands within about one voxel of the true surface — raise `worldResolution` or the collider's `radius` to place particles where you want them — and a particle that starts deep inside geometry has no direction to be pushed out along, so it is pushed up. The field is unsigned — it says how far the nearest surface is, not which side of it a point is on — so the world collider resolves against the segment the particle travelled this frame rather than against where it ended up. The march starts from the position the particle held last frame, which the previous resolve left outside, and stops where that path first comes within `radius` of a surface. Contact therefore lands on the side the particle approached from, and a step of any length is caught rather than carrying the particle through. The world collider is resolved by the built-in sprite update. A mesh emitter runs the mesh-instance update, which integrates without resolving colliders, so every collider it carries reports no contact. An emitter running its own WGSL binds no distance field, so the world collider reports no contact there while its other colliders resolve as that shader resolves them. Both are said out loud, once per emitter, the first time one runs. ## Shadow casting and render layers An emitter declares whether its particles block light and which render layers they draw on. Both reach the sprite path and the mesh path through the same value, so an emitter's kind decides neither one: ```lua local debris = particles.create({ mesh = "cube", maxCount = 300, castsShadows = true, renderLayer = "vfx", }) debris:setCastsShadows(false) debris:setRenderLayer("vfx fpsWeapon") print(debris:getRenderLayer()) -- "vfx fpsWeapon" print(debris:observe().castsShadows) -- false ``` `castsShadows` defaults to **false**. A caster is drawn into the shadow map as the geometry it is — a sprite emitter's quads as quads, a mesh emitter's copies as copies — so a soft alpha card casts the hard outline of its whole quad. That is right for debris, rubble and solid mesh copies, which declare it, and wrong for the smoke, dust and spark sheets that make up most of what an emitter draws, which leave it alone. `renderLayer` takes a layer name, an array of names, or a space-separated string, and defaults to `"default"` — the layer a renderable with no layer of its own sits on. A camera or a capture whose include spec names the layer draws the emitter and one excluding it does not, so a reflection probe, a portal camera, a minimap, a clean screenshot or an agent's `capture` takes the scene with the effect in it or without: ```lua capture({ renderLayers = "all !vfx" }) -- the scene, no emitters ``` Naming a layer interns it, which is what puts it in `renderLayer.list` and makes it addressable from a capture's include spec. Both are readable back — `:getCastsShadows()`, `:getRenderLayer()` — and both are reported by `observe()`, so what an emitter declares is checkable without capturing a frame and without reaching for the render host. ## Depth fade A particle card that runs into a floor, a wall or a prop draws a straight line along the intersection, which is what makes a large soft sprite read as a flat billboard. `depthFade` is the distance, in world units, over which the card dissolves into that surface instead: ```lua local smoke = particles.create({ maxCount = 400, rate = 60, lifetime = { 2, 4 }, size = NumberSequence.new(0.5, 3), depthFade = 1.5, -- world units }) smoke:setDepthFade(2.5) print(smoke:getDepthFade()) -- 2.5 print(smoke:observe().depthFade) ``` The quantity the distance is compared against is the straight-line distance between a fragment and the surface already drawn behind it, both taken in world space — so the ramp covers the same number of metres however far the camera stands from it. A fragment at least `depthFade` in front of that surface keeps its alpha whole; one standing on the surface is fully transparent; and one with nothing behind it keeps its alpha, there being nothing to dissolve into. The default is 0, which is off: an emitter that declares no fade draws through a program that reads no depth at all, and the frame it draws in copies none for it. Both emitter kinds take it — a sprite emitter's card and a mesh emitter's copy alike. The value has to be a finite number at or above 0; anything else is refused where it is declared rather than accepted and thrown once a frame. An emitter drawing an authored material (`material = ...` / `:setMaterial`) shades through that material's own shader, and fades over the distance that shader reads from the material's own `depth_fade`. The emitter says so once, because the material is shared by every entity drawing it and holds one distance for all of them. A particle material carries a fade by declaring a `depth_fade` float property, turning its shader's `DEPTH_FADE` feature on, and shading through a shader whose block for that feature includes `zero::scene_depth` and scales its alpha by `zero_scene_depth_fade(frag_coord.xy, world_position, depth_fade)`. `particle_sprite.shader` is the worked form. ## Custom WGSL update shaders Pass `updateShader = "/source/path/to/file.wgsl"` to `particles.create`. The shader must match the binding layout: ```wgsl // sprite emitter @group(0) @binding(0) var<storage, read_write> particles: array<f32>; @group(0) @binding(1) var<storage, read_write> vertices: array<u32>; @group(0) @binding(2) var<storage, read_write> params: array<f32>; // mesh emitter @group(0) @binding(0) var<storage, read_write> particles: array<f32>; @group(0) @binding(1) var<storage, read_write> transforms: array<f32>; @group(0) @binding(2) var<storage, read_write> instance_data: array<f32>; @group(0) @binding(3) var<storage, read_write> params: array<f32>; ``` Inside the shader, read per-frame data from the `params` array at the offsets documented in `particle_update.computeShader/shader.wgsl` (and exported as Lua constants from `particles.PARAM_LAYOUT`). A sprite shader writes the engine's standard 23-u32 Vertex layout into `vertices`; a mesh shader writes a column-major 4x4 per particle into `transforms` and four `vec4` lanes per particle into `instance_data`, the shape `particle_mesh_instance.computeShader/shader.wgsl` documents. User uniforms live at `params[32..63]`. Set them from Luau: ```lua system:setUserParam(1, 0.5) -- writes params[32] = 0.5 system:setParam("user1", 0.5) -- same ``` See `demos/particles_showcase/ParticlesShowcase.component/init.luau` for a worked example with a curl-noise field driving 4000 particles. ## Performance notes * **Compute pass cost** is proportional to `maxCount`, not to active count — dead slots still execute one workgroup invocation each, but only do the dead-check + degenerate-quad write (~10 instructions). * **CPU spawn cost** scales with the per-frame emit count (`rate × dt + bursts`), not with maxCount. A typical effect doing 100 particles/sec at 60 fps spends ~1.7 spawns/frame on the CPU. * **GPU memory** is dominated by the vertex buffer at `368 B/particle`. For 100 k particles that's ~37 MB. For 1 M particles ~370 MB — still fits on a mid-tier GPU but profile first. * **Sorting:** a sprite emitter that alpha-blends rewrites its own index buffer every frame, on the GPU, into the order that walks its particles back to front against the camera the frame is drawn from. While the emitter can be holding at most 2 048 live particles it does that in ONE compute dispatch (`particle_sort_local`: one workgroup sorts the live particles' depth keys in workgroup memory and writes the index buffer), so a step costs two dispatches, the simulation and the sort, whatever `maxCount` is, and the sort holds 32 B of buffers. Past 2 048 live it orders them by radix: a key pass, three dispatches per eight bits of key and the index write, eight dispatches at the default bucket count, over `maxCount`, in buffers of 12 B/particle plus a 1 KB digit histogram for every block of 256 slots. What a sorted emitter spends is dispatch overhead far more than per-particle work, so the dispatch count is the cost to read: eleven emitters of 2 100 slots holding ~800 particles each spend 22 dispatches a frame rather than 99. `sys:observe()` reports `sortPath` (`"local"` or `"radix"`), `dispatchesPerStep` for the population the emitter holds now, `lastStepDispatches`, and the running totals `computeDispatches`, `sortDispatches` and `localSorts`. An emitter that adds skips all of it: addition commutes, so its draw order cannot change its image. `sort = false` on the spec (or `sys:setSorted(false)`) turns it off; `sort = true` turns it on for an additive emitter. `sys:observe().sorted` reports which way an emitter resolved, and `getGpuBytes().sort` what the buffers cost it. The order is a total order on (depth bucket, slot): two particles the bucketing cannot tell apart keep slot order between them, and both paths produce the same order, byte for byte in the index buffer. `sortBuckets` is that resolution: 65535 by default, each bucket spanning 0.018% of its own depth, which at five metres is under a millimetre. The one-dispatch sort needs the bucket and the slot index to fit 32 bits together, which the default does for every emitter of up to 65 536 slots. On the radix path every eight bits of bucket index is one more radix pass and three more dispatches, so `sortBuckets = 255` sorts in five dispatches instead of eight at 2.7% of depth per bucket. `simulate` reorders once at the end of the prewarm rather than once a step: each step rewrites the index buffer the step before it wrote, so only the last step's order can reach a draw. What this orders is one emitter's particles against each other. Two emitters are two draws, and the renderer orders draws rather than the particles inside them, so two overlapping alpha plumes still composite by draw order. Particles composite against opaque geometry through the depth test, as they always did, and against other transparent surfaces by draw order. A mesh emitter draws instanced copies rather than an index buffer, and is not sorted. * **Frustum culling:** a sprite emitter's mesh AABB is set to ±10 000 m so per-emitter culling never trims active particles — emitter-level culling happens at the entity level via the host entity's transform. A mesh emitter's copies are culled one by one, each against the source mesh's own extent under that particle's matrix. A dead particle's matrix is zero, which parks its copy at the world origin with no area — it survives the cull whenever the origin is on screen and then emits no fragments. The submitted count is the slots the emitter has ever filled, not its cap: emission walks a write pointer from slot 0, so an emitter with a cap of 100 000 that has spawned five particles submits five instances. ## Roadmap (follow-up issues) The substrate is intentionally minimal. The follow-up issues track features that build on top: | Issue | Layer | |---|---| | #2674 ParticleEmitter component (38-property Roblox-shape surface) | shipped here as `deprecated/deprecatedParticles.package/DeprecatedSimpleParticleEmitter.component` | | #2682 GPU compute backend (VFX-Graph-shaped) | shipped here | | #2673 NumberSequence + ColorSequence Luau bindings | shipped here in Luau (Rust FFI is the future home) | | #2679 Emission shapes | shipped here | | #2680 Orientation modes | FacingCamera + FacingCameraWorldUp + VelocityParallel + VelocityPerpendicular shipped here | | #2678 Flipbook texture animation | future — needs texture-atlas UV math | | #2684 Particle ↔ world collision | analytic shapes and the scene's own geometry shipped here; see "Collision" below | | #2685 Force fields / curl noise | curl-noise demoed via custom WGSL; first-class ForceField component is future work | | #2681 LightEmission / LightInfluence HDR | brightness shipped; LightInfluence (read GI) future | | #2683 Mesh particles | shipped here — one instanced draw of the source mesh, placed and coloured per particle by the compute pass | | #2690 VFX editor (curve inspector, profiler) | future | | Back-to-front sorting for alpha-blended emitters | shipped here — see "Sorting" above | ## API reference See the `--!desc` doc-comments at every public method in `init.luau`, `curves.module/init.luau`, and `shapes.module/init.luau` for the authoritative API surface. `lsp.describe("particles/create")` and `lsp.search("particles")` from the engine also work after the engine has indexed the module.

# value_type Converts a **handle-backed value type** — `ColorSequence`, `NumberSequence` — between the live object a session holds and the durable payload its `serialize()` produces. A sequence has two forms: | Form | Shape | Meaning | |------|-------|---------| | live | `{ kind = "ColorSequence", __h = 13 }` | `__h` names a curve in **this process's** curve registry | | durable | `{ kind = "ColorSequence", keypoints = { … } }` | the curve itself, which any session rebuilds | `__h` is minted when the curve is created and is meaningful for exactly as long as that registry lives, so a record carrying it names nothing in the session that reads it back. The keypoints are the authored data, and they cross every boundary intact — which is why a record carries the durable form and a live component field carries the live one. Both forms carry `kind`, so a value read out of a component field says which converter owns it whether it came from memory or from a record. The two are told apart by which of `__h` / `keypoints` the table itself holds. `Field.table` copies the table it is handed and drops its metatable, so a live value read back off a component field answers no methods at all. The field gives that same stored table back on every read, so `bind` puts the methods on it once and the field answers them from then on. ## API ```luau local ValueType = require("modules.value_type") local color = ColorSequence.new({ 1, 0.3, 0.1 }, { 0.1, 0.1, 1 }) ValueType.kindOf(color) -- "ColorSequence" ValueType.isLive(color) -- true ValueType.isPayload(color:serialize()) -- true -- The keypoints out of either form. The second argument is the kind to read a -- bare `{ __h = n }` as, for a caller that knows its field's type. ValueType.keypoints(component.color, "ColorSequence") -- The durable payload for a live value; nil for anything else. ValueType.serialize(color) -- { kind = "ColorSequence", keypoints = { … } } -- The live value a payload names, rebuilt in this session; nil for anything else. ValueType.revive(record.color) -- A whole component field map, with every payload rebuilt. local applyData, rebuilt = ValueType.withRevived(record.data) -- Put the methods back on a value read out of a component field. ValueType.bind(component.color, "ColorSequence"):evaluate(0) ``` `withRevived` returns the **same table** when the map carries no payload, so the common case allocates nothing; the second return says how many fields were rebuilt. ## Consumers `scene_saver` asks per field as it serialises an entity, and writes the payload in place of the handle. `scene_loader` rebuilds the payloads in a component's record before applying it, so the component takes the field holding the same curve it held when the record was written. `dirty_hot_reload` does the same as it applies a body, and reduces the live side of its record comparison to the durable form so both sides are compared in one shape.

# assetType (asset type) The `assetType` is the **type of types** — the meta-type that every `<typename>.assetType/` folder is an instance of, including itself. A `<typename>.assetType/` folder declares a new asset type called `<typename>`: its on-disk shape, its identity rule, and the structural contract instances of the type must satisfy. This type is self-hosting. `assetType.assetType/` conforms to its own schema — a `type.yaml` plus a `README.md` — so the type system is defined in terms of itself rather than a hidden engine special-case (the same way a C compiler is written in C). Every asset in the engine, including each `.assetType` definition, now resolves to a registered assetType: a `.material` resolves to `material.assetType`, and `material.assetType` resolves to `assetType.assetType`, which resolves to itself. ## Why it exists Assets used to be mapped to their type *implicitly*, by matching the folder suffix against a name-keyed registry. That match carried no stored link: nothing on a `Foo.material` recorded *which* `material.assetType` it was written against, so two worlds shipping a same-named type could silently disagree. Making `assetType` a real, resolvable asset closes that gap — the link from an asset to its type is now an explicit reference pinned in the asset's `.refs` sidecar (`via: "asset_type"`), exactly like every other dependency. ## Where it lives - Source: `/zero/source/.../<typename>.assetType/` - Identity: `<typename>` (the `.assetType` suffix strips from the identity; the folder retains the suffix on disk). - Folder shape: - `type.yaml` — the structural spec the validator reads. **Required.** - `README.md` — type-level documentation. **Required.** - `about.yaml` — three short plain-language texts saying what the type is for (see "Say what your type is for" below). Every built-in type ships one. - `behavior.luau` — optional behavior/scaffolding module. - `template/` — optional canonical placeholder body the templater copies into a new asset of the type. - `<name>.module/` — optional shared code the type ships to **every instance** of it, conventionally `shared.module/` (see below). ## Shared code its instances reach (`asset.containing` + `.modules`) A type ships code every instance of it uses by declaring the modules in its own `behavior.luau`, as a map of tracked `require`s: ```luau -- inside <typename>.assetType/behavior.luau M.modules = { shared = require(".shared") } -- the sibling shared.module/ ``` An instance reaches it with one location-independent line: ```luau -- inside any foo.<typename>/init.luau local api = asset.containing(__FILE__).modules.shared ``` `__FILE__` is the chunk's own VFS path; `asset.containing` resolves the calling asset, and `.modules.<name>` follows the instance's pinned `typeRef` (the type's **guid**, recorded in the instance's `.refs` as `via = "asset_type"`) to the module its type declares. Because resolution follows that link rather than a category name, the same line in an instance of a different type resolves to that type's module, and identically-named modules in two types never collide. `asset.typeRef(target)` reads that guid for any target; `asset.resolve(asset.typeRef(target))` gives the full `AssetRef<assetType>`. See `assetTypes/README.md` § "Shared code: type-owned modules" for the full mechanism. ## How to create one Authoring a new asset type is just creating a `<typename>.assetType/` folder under `/zero/source/`. The engine registers `<typename>` as a category **the moment the folder is written** — no engine restart, no Rust change, and it works for built-in (`@builtin/assetTypes/`) and user-defined types identically. Once `<typename>` is registered, `<name>.<typename>/` folders are recognised as assets of that type and resolve their `asset_type` link back to this definition. Creating a `<name>.<typename>/` folder *before* its `<typename>.assetType/` exists fails fast: the suffix has no registered type, so the folder can't be a valid asset. Author the type first. ## Say what your type is for (`about.yaml`) Every type carries a small `about.yaml` beside its `type.yaml`, and the README you write for the type documents how to author an asset of it. Both are required, and both are meant to be written as you make the type, while you know what it is for. `about.yaml` answers three questions in plain words, one key each: ```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. Name the whole range of things it covers, in the words a game maker would use for them. - **`function`** is how it works today: what an asset of the type is made of and what the engine does with it. - **`usage`** is what a person or an agent does with one: how they pick it, place it, call it, or hand it to something else. A few habits keep it useful. Write about the type as a whole, so the text holds for every asset of it, and leave out any one asset's name. Say what the type does right now. Stay with words a game maker would say, and mention a file name or a call only where a game maker would know it. The limits are in bytes: `intent` 800, `function` 1500, `usage` 1200. Each is generous, and a few sentences usually say it. Why bother: agents working in a world read these three texts to learn what your type is for, so they reach for it when it fits and use it the way you meant. People searching find the type by what they want to make, and the three texts let them tell at a glance whether it is the one they need. `asset.create("assetType", name)` scaffolds the file with all three keys, and a README whose first paragraph is a `[[describe]]` note. Each value starts with `[[describe]]` followed by a note on what to write; replace the whole value with your own words. A value or a README line that still starts with `[[describe]]` counts as not written yet, which the push's check of each asset it carries against its type reports, naming the file. A type you leave as it was is not asked, so older types stand. Many types at once, or one you would rather not write by hand: `services describe` lists the types that lack these texts and what filling them costs, and `{ mode = "all" }` writes them into the same files, where you edit them like anything else you wrote. Where the texts show up: `asset.inspect("<typename>", "assetType")` returns them as `detail.about`, `assetTypeRef:getAbout()` returns them as a table with the keys `intent`, `function` and `usage`, the type's `types/<typename>` guide page ends with an "About this type" section holding them, and the Inspector's Type section lists them at the top. The guide page is this README plus that section, so a README that explains the type well and an `about.yaml` that says what it is for read well together. ## Ask your assets to say what they are A type can ask each of its assets to carry a description: a file, written by the author or generated, that says what that asset is and what it is for. The people and agents who find an asset read it to decide whether it fits, and the author knows what it is for at the moment of making it. **1. Declare the file with a `described` check.** This is the whole requirement: ```yaml files: required: - path: "README.md" # any file name works kind: "file" content: - { check: "described", message: "Say what this widget is for and where it goes." } ``` With that in place: - An asset whose file is missing, empty, or still has a line starting with `[[describe]]` does not meet the type's requirements. `asset.validate` names it, `zm status` and `world.publishBlockers()` list it, and a push that carries it is refused with `message`. - `services describe` finds it (`mode = "find"` lists it and the price) and can write the description for it (`mode = "all"`). It writes only this file. For a YAML file that holds several texts, name the keys and their limits in bytes, the way this type does for `about.yaml`: ```yaml content: - check: "described" keys: - { key: "intent", max_bytes: 800 } - { key: "usage", max_bytes: 1200 } message: "Write intent and usage." ``` `headings` names sections a Markdown file must have. `assetTypes/README.md` has the full check. **2. Optionally, steer what gets generated with a `describe:` block:** ```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>" ``` `guidance` says what a description of your type covers, and `examples` names assets whose descriptions show the shape you want. Without the block, generation still works from the general describing guide and the check's `message`. An example is an asset of your type in the library whose description is a true, written one, never a scaffold's placeholder, and never the asset being described. When the library has none, leave `examples` empty rather than name one that is not. A type whose assets the model cannot perceive (a sound it cannot hear, a motion it cannot see) says so in `guidance`: the description comes only from what the asset's own files state, such as its name and the `.metadata` where a generation service records the prompt that made it, and when they state nothing the model answers `cannot` with that reason. `services describe` then fails that one asset with the reason and leaves its file as it was. **3. Start the file unwritten in your template.** Put a heading and one line that starts with `[[describe]]` and a short note on what to write, in `template/<file>`, so a new asset starts unwritten rather than with text that only looks written. Do not put example content in it: every new asset carries the template verbatim, and the same text on many assets makes them impossible to tell apart in search. Types whose assets say what they are through their own content (a mesh, a texture, a sound) leave this out: declare nothing and nothing is asked. ## The `behavior.luau` contract `behavior.luau` is the type's code. It returns ONE table, and the keys below are the ones the framework reads off it for EVERY type — the surface you get by declaring them. Anything else on the table is your own: reachable by name through `require("@builtin::assetTypes.assetType.shared.ref").loadTypeModule("<typename>")` for a system that knows your type (`computeShader` publishes `dispatchKey` that way), and never called by the framework. ```luau local M = {} M.ref = { ... } -- methods on every AssetRef of this type M.modules = { ... } -- shared code the instances reach M.global = {} -- reserved key; ship the empty table function M.onCreate(name, opts) ... end return M ``` ### The tables | Key | Shape | What the engine does with it | |-----|-------|------------------------------| | `M.ref` | `{ [name] = function(self, ...) }` | Every function becomes a method on every `AssetRef` of this type: `ref:name(...)`, with `self` the ref. This is how a type gives its instances an API. Two names in here are contracted — see below. | | `M.modules` | `{ [name] = require(".sibling") }` | Shared code the type's instances reach through `asset.containing(__FILE__).modules.<name>`, resolved by the instance's pinned `typeRef` guid. See the section above. | | `M.refShapes` | `{ [method] = "TypeName" }` | Declares the result type of a `M.ref` method so the LSP can check what a call site does with it. See the `M.refShapes` section below. | | `M.events` | an events schema | The events an ASSET of this type fires, declared the way a component declares its own. Readers subscribe through `ref.events.<name>:connect(...)`; firing authority stays with the type. Keyed by the asset's guid, so every resolver of the same asset shares the signals and a re-resolved ref re-attaches to subscriptions already there. | | `M.namePattern` | a Lua pattern string | The name shape `asset.create` enforces for instances of this type, replacing the default `^[A-Za-z][A-Za-z0-9_]*$`. | | `M.global` | `{}` | Reserved. Ship the empty table. | ### The lifecycle hooks Each is optional; a type that omits one costs nothing. The engine calls them: | Hook | Signature | When it fires | |------|-----------|---------------| | `M.onCreate` | `(name, opts) -> { [filename] = contents }` | On `asset.create("<type>", name, opts)`. Returns the files that scaffold the new instance, as a map of relative path to contents; the framework writes them. The `opts` type annotation is the schema `asset.create` validates the caller's arguments against, so annotate it. | | `M.onReplace` | `(dest, files) -> { [filename] = contents }` | On an `asset.create` that writes over an asset already at `dest`, after `onCreate`. Receives the files `onCreate` produced and returns the files to write, so a type that re-derives its content (a rig re-imported from its source file) can carry what an author added to the asset it replaces. Optional. | | `M.onRegister` | `(self)` | Once per instance, the first time it registers: on `engine.onWorldLoaded` for instances already in the world, immediately on a live `asset.create`, and when an instance arrives after that sweep (installed, pulled, or synced from a peer). Guarded by the instance's path, so a double trigger never double-registers. An instance that leaves the runtime releases the guard, so one arriving at the same path again registers. This is what makes "write an asset into the world and it takes effect live" work for content that registers into a runtime registry. The `@builtin` library is excluded from the sweep. | | `M.onChange` | `(ref, change)` | On every VFS write to a file INSIDE one of this type's instances. `change` is `{ path, asset, type, kind, origin }`: `kind` is `"edited"` or `"seeded"`, `origin` is `"local"` or `"remote"` (an importer runs on the originator only). **Filter on `change.path`**: the hook fires for any file under the folder, so act on the one you care about. It runs as its own task and may wait on what it reads: a `vfs.read` of bytes only the blob store holds (a binary file on the web build) fetches them. The writes to one asset reach the hook in the order they were made, each once the hook before it has finished. A re-entrancy guard suppresses writes back into the same asset routed inline from the hook, and a write the hook makes is routed on a later frame like any other, so the hook must be convergent on its own: diff the meaningful state and short-circuit while your own regeneration is in flight. | | `M.onDelete` | `(ref)` | When an instance of this type leaves the runtime: it is deleted, or the engine swaps away from the world binding that held it. Its files are gone from `/zero/source` by then. A removal routed while the instance's `onChange` is waiting reaches `onDelete` once that hook, and every write queued behind it, has finished. On a swap the instance still exists in the world it belongs to, and a VFS write the hook makes reaches the world now bound. | | `M.validate` | `(assetRef) -> { { code, message, severity? } }` | On `asset.validate`, after the structural `type.yaml` check, for the type's own SEMANTIC validation. `severity` defaults to `"error"`; error-severity problems flip `ok` to false, warnings do not. A hook that raises or returns a non-table is itself reported as a `validate.hook_failed` error. `world.push` runs this per user asset, so declaring it enforces your type's rules at publish time with no further wiring. | ### The two contracted `M.ref` names Most `M.ref` methods are your type's own surface: name them what you like, return what you like. Two are read by the engine and mean the same thing for every type, so their shape is fixed: - **`instantiate(self, target?, opts?) -> (root, idMap)`** — makes an instance part of the scene. Defining it is the whole opt-in: `ref:canInstantiate()` is true exactly when it exists. Its **return is a contract** — see the next section. - **`inspect(self) -> detail`** — the type-specific half of `asset.inspect`. See its section below. ### Names a type cannot shadow Some keys resolve on every `AssetRef` before per-type dispatch, so an `M.ref` entry of the same name is never reached: `canInstantiate`, `getSource` / `getBytes` / `getText`, `exists`, `deps`, `meta`, `runtime`, `events`, `modules`, `typeRef`, and the residency flags `has_backing_asset`, `has_runtime_changes`, `cpu_resident`, `gpu_resident`. These are the behaviours every asset must expose identically, which is why they win. ### Reloading A `behavior.luau` edit ripples to existing refs with no restart: dispatch reads `mod.ref` fresh each time and `require`'s cache is re-run in place. A type whose folder appears at runtime is picked up on the next dispatch — negative results are not cached either. ## The names your type's assets hold (`references:`) An asset that names another asset by a string depends on it: the named asset travels with it into a pack or a pull, and a name nothing answers to is an unresolved dependency `worldValidation` reports and the push gate refuses. The engine reads `require(...)` and the asset lookups on its own; a name your type's format or API carries anywhere else is one you declare, in `type.yaml`: ```yaml references: # A top-level key of this type's own files that holds a name (or a table of them). keys: - { key: "shader", type: "shader" } # A call's argument, counting from 1, wherever the call is written. args: - { call: "g:node", position: 2, type: "procNode" } # A field of the options table a call takes. fields: - { call: "fx.beam", field: "material", type: "material" } ``` `type` is the category the name resolves in, one of `asset.categories()`. An argument declared once per category, at the same `call` and `position`, takes the name from whichever category answers. A key or a field holds one category: declared again with another `type`, it takes the later one. The block is declared as the type registers, when the library or the world holding it is laid into the VFS, so every reference table reads it whatever script has or has not run. `asset.declareReferenceKey`, `asset.declareReferenceArg` and `asset.declareReferenceField` declare the same things from a script, for a surface that is no type's. ## What search does with your type (`indexing:`) A type declares what search embeds for its instances. **This is not optional and there is no useful default**: ZeroMind runs your declaration and adds nothing of its own, so anything you do not point at is absent from the index — silently, and for every instance of the type forever. Twenty types once shipped with no `indexing:` block and every instance of them was unfindable. A type whose instances are never searchable (a run record, a log) says so with `indexing: none`; every other type declares a recipe. A type without an `about.yaml` beside its `type.yaml` refuses every push that carries it, whether or not the push edited the type. Texts in it that are not written yet follow the rule every `described` file follows: they refuse the push that edits, stages or commits the type. Two words carry the whole thing, and they are the same two the search tool exposes: - **`identity`** — what an instance IS. For anything you can look at, that is the picture (`content:` + `modality: image`, matched directly by a text query). For everything else it is the authored text that says what it is. - **`capability`** — what it DOES and how it is made. Code, settings, the model-written summary of them. A type with no behaviour has no `capability` entry. A type with nothing to look at has no image. Leaving a slot empty is a statement; filling it with whatever happens to be lying around is not. The one you have to decide when authoring a type is: *for an instance of this, what is the thing a person would recognise it by, and what is the thing it does?* A texture answers "the image" and "its compression settings". A module answers "its README" and "its code". Write those two answers into `indexing:` and the rest follows. Three specifics worth knowing before you write one: - **`derive` is instructed by this type's own `README.md`.** A model reads an instance's source and writes a description; what it embeds is the description, not the source. It follows your README to know what it is looking at, so a type whose README says what its instances are gets good derivations for free. There is no prompt to name. - **`derive` loses detail.** It keeps the main technique and drops secondary ones. If the source is code you want searchable by its own vocabulary, declare the same files a second time as `capability` with `extractor: verbatim`. Two entries, same role, different failure modes. - **Never `source: { field: name }`.** A filename is one or two words with no usable embedding, and a corpus indexed that way answers "language runtime" with `say_runtime_2.soundClip`. `facets:` is the second stage: a `file:` embedded whole (`.metadata`, so keys nobody declared still get indexed) plus computed keys that state a value for every instance including `false` — the raw file can imply "not rigged" and can never say it. The full schema, every extractor and the facet sources are in [`assetTypes/README.md`](../README.md); the scaffolded block with inline guidance is in [`template/type.yaml`](template/type.yaml). ## A container whose contents work together (`system: true`) A type that is a container can say its contents are one working whole by declaring `system: true` at the top level of its `type.yaml`. `package` declares it: the components, modules, scenes and tools a package ships are parts of one system. The declaration is plain data, read from the decoded `type.yaml` (`require("@builtin::assetTypes.assetType.shared.declaration").of("package").system`), and a type that leaves it out is an ordinary type. ## What your type looks like (`preview:`) A type declares how its instances are pictured, and the engine makes the picture when something needs it: staging an instance whose `preview.png` is missing or pictures content it no longer holds queues a render, a view that shows the instance asks for one, and `ref:preview()` renders one on demand. An edit renders nothing on its own. Each `preview.png` records the content it pictured, which is how a stale one is told from a current one. The preview studio owns the light, the backdrop, the framing and the camera, and nothing in the world reaches it, so an instance pictures the same in every world. Declare one of four recipes: | `kind` | The picture is | Your type provides | |---|---|---| | `instantiate` | the asset stood in the studio through its own `instantiate` | `ref.instantiate` | | `image` | a file the instance holds, fitted to the frame, nothing rendered | `source.files`, the candidate files in order | | `surface` | the asset painted on a builtin mesh | `mesh`, and `ref.previewMaterial(self) -> { material }` | | `custom` | whatever `ref.preview(self, opts)` returns | `ref.preview` | ```yaml preview: kind: surface mesh: sphere ``` A scene-instantiable type that declares nothing still answers `ref:preview()` through its `instantiate`, but persists no picture: the declaration is what makes the engine keep one. List `preview.png` among the type's files so an instance may hold it. The picture is findable only when `indexing.content` names it. The two are separate statements, and neither is derived from the other: ```yaml indexing: content: - role: identity modality: image source: { file: "preview.png" } ``` `@builtin::assetTypes.assetType.shared.previewRecipe` reads the declaration; the scaffolded block with inline guidance is in [`template/type.yaml`](template/type.yaml). ## Typing a result from the instance (`M.refShapes`) Every method on `M.ref` is checked against the type its `--!return` names, and every asset of the type gets the same one. That is right for most methods and wrong for the ones whose result is shaped by the ASSET: a method answering one entry per child folder, per row of a config, per binding an input map declares. The widest true annotation for those is `{ [string]: Thing }`, and an indexer accepts every key — so a caller's typo reads as valid and nothing reports. `M.refShapes` lets the type state the result per instance. Each entry is `function(self) -> (typeExpression, source?)`: a Luau type expression for THIS asset, and the module whose type vocabulary the expression uses. Read the asset; never run it — stating a type must not take effect. ```lua -- inputMap.assetType/behavior.luau — the shipped example. -- `activate()` hands back one handle per control the map declares. 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)` resolves and `map.noexisting` is reported with the map's real controls. Without it, both pass silently. ### What the call site has to say A per-instance type is matched by the asset's IDENTITY, so it applies only where the reference the method is called on says WHICH asset. Two spellings do: ```lua -- a component field, whose declared default names the asset public = { map = Field.assetRef("inputMap", "@builtin::inputMaps.default", Sync) } local controls = public.map:activate() -- typed for THAT map -- an annotation, naming category and identity local m: AssetRef<"inputMap", "@builtin::inputMaps.default"> ``` `asset.resolve("<identity>", "<category>")` carries the CATEGORY, so the methods the category defines are checked on the result — but not which asset it found, so a per-instance result keeps the category's declared return. A reference that names no asset (`asset.resolve(someVariable)`, a value passed in as a parameter) carries neither, and calls on it are unchecked. That is the same rule everywhere: the checker states what the code states, and a name computed at runtime states nothing. ### The result is a value, not a binding The type belongs to the expression, so it travels the way any inferred type travels. Indexing the call's result is checked; stashing it in a module local and indexing it from another function is not, because the local's declared type is what carries across — and `any` (or no annotation) carries nothing: ```lua -- checked: `d.greting` is reported function awake() local d = public.dialogue:lines() d.greeting:say() end -- NOT checked: `lines` is a module local typed `any` local lines: any = nil function awake() lines = public.dialogue:lines() end function start() lines.greting:say() end ``` Bind what you need at the call site and the names stay checked in both places — the asset-derived type at the boundary, ordinary scoping after it: ```lua local lineGreeting = nil function awake() local d = public.dialogue:lines() lineGreeting = d.greeting -- `d.greting` is reported here end function start() lineGreeting:say() end ``` ### When nothing is reported and you expected something From a call site, a type that is correct and a type that was never published look the same: no diagnostic either way. `require("@builtin::assetTypes.assetType.shared.refShapes").published()` answers which it is. It returns two maps — the category surfaces, and the per-asset results keyed by identity and then by method: ```lua local shapes = require("@builtin::assetTypes.assetType.shared.refShapes").published() shapes.categories.dialogue --> "{ lines: () -> any, lineNames: () -> { string } }" shapes.returns.Shopkeeper.lines --> "{ browsing: Line, farewell: Line, greeting: Line, wares: Line }" ``` An identity absent from `returns` was never published for, which is a different thing from published-and-correct — and the reason to look here rather than at the call site. The answers are recomputed when an instance is written, so a control added to a map reaches the checker with no restart. Only types that declare `refShapes` are read per instance, and at most 64 assets of one type are — past that the type keeps its declared return and the engine log names what was dropped. ## The instantiate hook (`M.ref.instantiate`) — a contracted return A type opts into becoming part of the scene by defining `instantiate` on its `ref` table. That is the whole opt-in: `ref:canInstantiate()` is true exactly when the hook exists, so consumers offer a scene path — an `Asset.source` field, a viewport drop, a tool argument — by CAPABILITY rather than by a list of type names. Unlike `inspect`, this hook's **return is a contract**. A caller writes one piece of code against every instantiable type, so what comes back cannot vary by type: ```lua -- behavior.luau local Instantiable = require("@builtin::assetTypes.assetType.shared.instantiable") local M = {} M.ref = { instantiate = function(self, target, opts) local root = Instantiable.root(self, target, opts) -- IN: the base opts -- ... compose whatever this type is, under `root`, NOW ... return Instantiable.result(self, root, idMap) -- OUT: the contract end, } return M ``` **IN.** `target` is an owning entity ref: the instance lands under (or, for a hierarchy type, onto) that owner. With no target the type spawns a fresh root. `position`, `rotation`, `scale`, `name` and `temporary` mean the same for every type — `Instantiable.root` applies them to a root you mint, `Instantiable.place` to one you adopt, so you never re-read the spec. Honour more opts of your own if your type needs them, and document them in the hook's `--!arg` docs. **OUT.** Return `(root, idMap)` through `Instantiable.result`: - **`root`** — the composed root, as an `EntityRef`. Composition is **synchronous**: everything your type builds is live when you return, so the caller can parent to it and read its components in the same statement. Do not defer the work to a component's `awake` and return an empty shell — a root that is not live is refused. - **`idMap`** — the `originalId -> runtimeId` map naming what you spawned, or nil for a type with no addressable children (`result` normalises it to `{}`). **A caller never receives nil.** A component that re-composes your asset on every load keeps this map and passes it back in, which is how a cross-entity reference into the composition survives a reload. `AssetRef` runs every `instantiate` through `result` on the way out whether or not your type called it, so returning something else fails at your own call rather than handing a caller a nil root. Calling it yourself is still how you say what you return, and running it twice changes nothing. `@builtin::assetTypes.assetType.shared.instantiable`'s README is the full reference for both halves. ## The inspect hook (`M.ref.inspect`) `asset.inspect(ref)` resolves `ref`, builds a common envelope shared by every asset (`identity`, `name`, `guid`, `source`, `typeName`, `typeDefinitionPath`, `scope`, `origin`, `description`, `tags`), then calls the resolved type's own inspect hook — `M.ref.inspect(self)` on `behavior.luau` — for the type-specific `detail`. The hook returns *only* `detail`; the framework fills in everything else: ```lua -- behavior.luau local M = {} M.ref = { inspect = function(self) -- self.path is the asset's own folder. Parse the asset's OWN -- files — source text, a native payload header, its `.metadata` -- — never runtime state (a live component instance, a GPU -- upload, a compiled schema): inspect must work on an asset that -- hasn't been compiled, uploaded, or registered yet. return { -- type-specific fields, whatever this type wants to surface } end, } return M ``` A type that omits `M.ref.inspect` yields the generic record: the envelope alone, `detail = nil`. That's a valid, working state — not an error — but it means agents calling `asset.inspect` / `tools.use("assets","describe", ...)` on an instance of the type see only identity and scope, none of what makes an instance of it meaningful. Declaring the hook is what makes a type's instances inspectable for what they actually are. A hook that raises leaves `detail = nil` and sets `record.warning` to the error text — `asset.inspect` itself never raises for a resolved ref. ## Discovery - `asset.list("assetType")` — every registered asset type. - `asset.inspect("<typename>")` — the type's identity, source path, and this README, plus its `about.yaml` texts as `detail.about`. - `asset.resolve("<typename>", "assetType")` — the `<typename>.assetType` asset itself (used by the validator to find the type's `type.yaml`). ## Related - `assetTypes/README.md` — the full `type.yaml` schema and validator rules. - `@builtin::assetTypes.assetType.shared.instantiable` — the instantiation contract's shared implementation, both halves. - Every other `*.assetType/` here — the concrete types built on this meta-type. ## The Inspector a type ships Every type names the file its Inspector sections come from with `inspector: { type: "inspector.luau" }` in its type.yaml. `asset.create("assetType", name)` scaffolds the block and an `inspector.luau` whose Contents section lists an asset's files, built from `ctx.parts`. `asset.validate` on a type that names none reports `assetType.inspector_required` (an error for a `@builtin` type the engine's library authors; a warning for a world's own, and for one the library carries by reference, which the world that published it answers for), and one whose file does not load `assetType.inspector_invalid`. ## In the Inspector Type: what the type.yaml declares (suffix, container, primary files, the settings and inspector blocks), whether the type ships a behavior, how many instances it has, and **Open** for its files. Schema: the settings every instance carries, as read-only typed controls at their defaults (a type whose schema is per instance says where it is declared). Instances: a link to each of the first 20 assets of the type, and how many there are when there are more.

# 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. 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()`. Globals leak across reloads. 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**.

# deprecatedParticles (deprecated) > **Deprecated.** This belongs to the earlier particle substrate. It stays loadable by identity and guid for content that already uses it; nothing new should use it, and search does not offer it. Particles are procgen sim nodes (`sim.spawn`, `sim.particles`, `sim.shader`) played through an effect: use `@builtin::assetTypes.effect`. The package holds the GPU particle engine module (`engine`), the `deprecatedParticles` module over it, the `DeprecatedParticleEmitter` and `DeprecatedSimpleParticleEmitter` components, the shaders, compute shaders and materials they draw with, and a demo scene. The package's `.metadata` carries the deprecation marker, so every asset inside is deprecated.

# 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.settings Resolves four questions about an asset's typed settings, all answered from its type's `type.yaml` — nothing here is found by convention. ```lua local Settings = require("@builtin::assetTypes.assetType.shared.settings") -- or, from inside the assetType runtime: local Settings = require("@builtin::assetTypes.assetType.shared").settings ``` ## Where does a type's schema live? `type.yaml` names it in a `settings:` block: ```yaml settings: values: "settings.yaml" # where an instance's own values live schema: { type: "settings.luau" } # one schema for every asset of this type ``` or, for a type whose settings differ per instance (an importer): ```yaml settings: values: "settings.yaml" schema: { instance: "settings.luau" } ``` or, for a type whose schema is a table its instance's own source declares and whose values live elsewhere (a component: its `public` fields, valued on each entity it is on): ```yaml settings: schema: { instance: "init.luau", export: "public" } ``` Whether an instance may lack its schema file is what the type's `files:` block says of that file. Listed under `files.optional`, it may be absent, and an instance without it declares no settings — the importer type lists it there, since most importers take none. Listed under `files.required`, or not listed at all, it must load, and an instance missing it is a broken declaration and is logged. `schema.type` is required at the folder relative to the TYPE's own `.assetType/` directory (one schema shared by every instance). `schema.instance` is required relative to each INSTANCE's own folder (`init` resolves the instance's own identity; anything else is a sibling module under it). Without `schema.export`, the file is required as a module and its return value IS the schema. With `schema.export`, the file is run in an environment of its own and `export` is read from a returned table carrying it, or else from the globals the file assigned — a component's `public` is such a global. That environment reads through to `_G` and takes every write itself; its own `_G` is itself, its `declare` and `computed` record into it, and its `task` records spawned, deferred and delayed work instead of starting it. Every other global is the real one, so a call the file makes through one runs as it does anywhere. The schema is the declared table's Field descriptors. A schema that resolves to nothing says why through `Settings.schemaProblemOf(ref)`: the file could not be read, compiled or run, or declared no such table. An instance schema is read again when its file, its type's `type.yaml`, or the entry file of any module the asset `require`s changes. `Settings.blockFor(typeName)` returns the raw block; `Settings.schemaForType(typeName)` and `Settings.schemaOfInstance(ref)` resolve the two schema shapes respectively; `Settings.schemaFor(ref)` tries the type-level schema first, falling back to the instance-level one. `ref` naming an assetType asset itself — e.g. `asset.resolve("texture", "assetType")`, rather than an instance of it — reports that type's own declared schema, the same one every instance of it reports. ## Where do an asset's values live? `settings.values` names a file living beside the asset's own content — `Settings.valuesPathOf(ref)` joins it onto the asset's path. `Settings.valuesOf(ref)` / `Settings.writeValues(ref, values)` read and write it; this module only names where it is. A type that declares its schema with no `settings.values` keeps no values in the asset — a component's live on each entity it is on — so `valuesOf` answers nil for it, `asset.create` refuses a `settings` table for it, and `asset.setSettings` refuses a write. `Settings.recordedWrite(path, text)` writes a file the way every values file is written, and an editor uses it for any other file it writes. It writes the whole contents, records the write into the open undo operation when one is open (so undoing it restores what the file held), and raises when the write does not land. ## In what order are a schema's fields declared? Every `Field.*` constructor stamps its descriptor with `declaredOrder`, one more than the last. Luau evaluates a table constructor's entries in the order they are written, so `Settings.orderedNames(schema)` lists a schema's fields — and a struct's subfields — in the order the source writes them. A values file, or a legacy `.metadata` settings block, may hold an older spelling — a renamed field, an older enum member. Every read passes what is stored through the type's `normalizeSettings` (`Settings.normalizeFor`), so it answers in the fields the schema declares today, and writes nothing. The next local edit of that asset rewrites the file in the declared spelling (`Settings.healLegacyIfNeeded`). `asset.setSettings(ref, patch)` writes a partial patch: `Settings.resolvePatch(ref, patch)` normalises it, merges it over the current values and applies the type's derived defaults for the fields it changed, and `Settings.writeValues(ref, values, patch)` applies the corrections, checks the schema and writes the file. ## How is a new asset's settings resolved at creation? `asset.create` calls `Settings.resolveForCreate(typeName, name, destPath, creationOpts, callerSettings, importerSettings)` before running the type's `onCreate`, checks the result against the schema, writes it to the values file, and hands `onCreate` a COPY of it as `opts.settings` (`Settings. cloneValues`) — never the same table the values file gets, so nothing `onCreate` does to its own copy can reach what was stamped. `onCreate` reads settings from `opts.settings` and never writes to it. `asset.create` also seeds the change baseline with the stamped values (`Settings.seedChangeBaseline`), so the values file's own first dispatch reports nothing changed and the payload `onCreate` encoded is the only encode a create runs. The layers, lowest priority first, each overriding the ones before it field by field: 1. The schema's own declared defaults (`Settings.defaultsOf`). 2. The type's own `settingsDefaults(name, opts, asked)` hook, when its `behavior.luau` exports one. `asked` holds what layers 3 to 5 name, so a default can follow a field one of them sets. 3. The Preset Manager's matching row (`Settings.presetLayerFor`). 4. The creating importer's settings for this type. 5. The `settings` table the caller passed to `asset.create`. 6. The type's own `settingsDerivedDefaults(values, explicit, changed)` hook, when its `behavior.luau` exports one — a field whose default follows another field, set only when no layer from 2 to 5 named it. 7. The type's own `settingsCorrections(values, name, opts)` hook, when its `behavior.luau` exports one — applied last, once every other layer has merged. Layers 2 to 5 are each read through the type's `normalizeSettings`, so a layer naming a field in an older spelling sets the field it names today. `asset.create`'s top-level settings alias accepts those older names too (`Settings.acceptedFieldNames`). Layer 7 is `Settings.applyCorrections(typeName, values, explicit, context)`, the one corrections path every settings write takes — this create chain, and `Settings.writeValues` for every later write (`asset.setSettings`, a type's first-encode seed, the legacy heal). `explicit` names the fields the writer asked for: the caller's `settings` table here, the patch for `asset.setSettings`. A correction lands SILENTLY on a field the writer did not name — nobody asked for that value, so overriding it just states a fact. A correction that contradicts a field the writer named REFUSES the write, naming the field, the value asked for, and why it cannot hold — the same as every other place this codebase refuses an explicit request it cannot satisfy (a `Field.checkSchema` violation, a BC7 alignment error) rather than silently rewriting it into something else. So `asset.setSettings(tex, { compression = "rgba16" })` on a mipped texture stores `generateMipmaps = false` beside it, while `asset.setSettings(tex, { compression = "rgba16", generateMipmaps = true })` is refused. `Field.checkSchema` runs once, over the result AFTER the corrections hook has applied — a bad value nothing corrects refuses the creation. ### Four hooks, four different jobs Every hook is an optional export on a type's `behavior.luau`, alongside `onCreate` / `onChange`. **None is ever handed a table to mutate** — each reads what it's given and RETURNS a table of what it wants changed (or nil); `resolveForCreate`, `resolvePatch`, `applyDerivedDefaults` and `applyCorrections` are the only places that write to the values, by merging what a hook returns the same way every other layer merges. - **`normalizeSettings(values) -> values`** maps every older spelling a stored file or a write may carry to the field and member the schema declares now, returning a new table; a table naming both an older field and its replacement keeps the replacement. The companion export **`normalizedSettingNames = { ... }`** lists the older field names it accepts beyond the schema, so a write naming one is not refused as an undeclared field. `texture.assetType`'s maps the fields its earlier schema stored to `colorSpace` + `compression`, and the older `filter` keywords to `linear` / `nearest`. - **`settingsDerivedDefaults(values, explicit, changed) -> partial?`** answers the values of fields whose default follows another field. At creation `changed` holds every field; on a write it holds the fields the write moved. A returned field applies only where `explicit` — the fields the writer named — does not name it. - **`settingsDefaults(name, opts, asked) -> partial?`** supplies a DEFAULT the schema itself has no syntax for — something only knowable at creation time, like a naming convention, a fact read off a payload the caller handed in, or a value that follows a field a higher layer sets (`asked` holds what the Preset Manager, the importer and the caller name, the higher one's value where two name a field). It runs early (layer 2 above), so any later layer — Preset Manager, importer, caller — freely overrides it. `texture.assetType`'s returns the `textureType` the name suggests (a `_normal`-suffixed name is a `normalMap`), `compression = "uastc"` and `maxDimension = 4096`, with `rgba8` for a `textureType` of `sprite` that a higher layer names; for a pre-encoded ZTEX payload it returns the colour space, compression and sampler the payload's own header carries. Either way, an explicit `settings = { ... }` from the caller still wins. - **`settingsCorrections(values, name, opts) -> (partial?, reasons?)`** enforces a CROSS-FIELD CONSTRAINT the schema itself has no syntax for — a fact about one field that depends on another field's resolved value, true regardless of which layer produced that value. It runs last (layer 7 above), over the fully merged `values`, and again on every later write of the values file. Nothing is left unmet in what gets validated and stamped — but a value the caller explicitly asked for is never silently rewritten to satisfy it; `applyCorrections` refuses instead (see above). The optional second return, `{ [field]: reason }`, supplies the "why" for that refusal message; a field with no reason falls back to a generic one. `texture.assetType`'s returns `{ generateMipmaps = false, maxDimension = 8192, colorSpace = "linear" }` whenever the RESOLVED `compression` is high-precision (the encoder stores one verbatim, linear, and refuses a mip chain or a downsample for it outright), paired with a reason naming the compression, and `nil` otherwise. ## What does a declarer declare? `Field.settingsOf(identity, mode)` embeds another declarer's schema as a struct field without restating it. The identity names one of two kinds of declarer, and `Settings.schemaOfDeclarer(identity)` tells them apart by what `identity` resolves to: - **An assetType** (e.g. `"@builtin::assetTypes.texture"`) — embeds the schema every instance of that type carries, resolved via `schemaForType`. This is the type-level shared schema from the section above, not a per-instance one — an assetType has no settings of its own to declare per instance. - **Anything else** (an importer, or any other asset that declares settings of its own) — embeds that asset's own schema, resolved via `schemaOfInstance`. Every schema this module serves has already run its `Field.settingsOf` fields through this resolution — a caller reading `schema.someField.fields` never sees an unresolved `declarer` with no `fields`. Resolution descends into an already-literal struct's `fields` and a list's `element` the same way, so a declarer embedded several fields deep is still reached. A declarer that embeds itself, directly or through another declarer, stops one level short of the loop instead of recursing forever. ## What are the defaults? `Settings.defaultsOf(schema)` reads every field's declared `default` into a plain table — a field declared without one is absent from the result rather than holding a `nil` value.

# AreaLight A rectangular light source on an entity. The rect is centred on the entity's world position, faces along the entity's world rotation applied to `face` (default "Front", the entity-local -Z that `transform.forward` reports and that `entity:lookAt` aims), and spans `width` by `height`. A rect under a carrier moves and turns with it. Its light arrives from a surface rather than a point, so shading falls off gradually across a wall, highlights stretch to the shape of the source, and shadows carry a penumbra that widens with the rect's size and the caster's distance.

# BoxCollider (component) A box collision shape. Works with or without a `Physics` component: on its own it is static collision geometry, and alongside one it moves with the body. ## Sizing `half` is the box's half-extents in the entity's local space, multiplied by the entity's world scale. Leave it unset and the box derives from the entity's model bounds, so a bare `BoxCollider` matches what is rendered at any scale. ```lua entity.find("crate").component.add("BoxCollider", {}) -- fits the mesh entity.find("wall").component.add("BoxCollider", { half = { 2, 4, 0.2 } }) -- authored ``` ## Fields | Field | Meaning | |-------|---------| | `half` | Half-extents. Unset derives from model bounds. | | `isTrigger` | Report overlaps without blocking. | | `friction` | Surface friction. | | `restitution` | Bounciness. | ## Composing A collider on a child entity attaches to the nearest ancestor carrying a `Physics` component, so a body made of several shapes puts each on its own entity and each keeps its own material and trigger flag. Past a few dozen boxes sharing one material, `CompoundCollider` is cheaper: it is a single broadphase volume where separate components are one each.

# 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.