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

# WheelCollider A wheel of a ray-cast vehicle (Unity-style). Add it to a child entity of a rigid body: every wheel under one body is one wheel of that body's vehicle, simulated by rapier's ray-cast vehicle controller (`DynamicRayCastVehicleController`). The system finds the nearest ancestor with a `Physics` component and drives it. Each physics tick a wheel casts its suspension ray straight down the chassis' local **-Y** from its own position, which is the suspension **mount**. The ray passes through triggers and through the chassis' own colliders, so a chassis `BoxCollider` around the mounts is fine. The wheel stands on the nearest surface along the ray whose normal faces back along it within `groundAngle` (45 degrees by default); the ray reads past a steeper face, such as the side of a crate, a kerb's face or a wall, to the ground beyond it, so a wheel meets a box on the road on its top. The controller then applies the suspension, drive, brake and tyre grip to the chassis as impulses, and the opposite of each, at the tyre's contact, to the dynamic body the wheel stands on: a car parked on a deck, a seesaw, a soft body or another car weighs on it as the same chassis resting on it directly does, and a car that drives or brakes on a floating deck pushes the deck the other way, the two sharing one momentum. The push into that body reaches it whole where its contacts hold it up, as a deck or a crate lying on the floor is held, and where it would throw a light body out from under the tyre, or tip it about the edge it stands on, it reaches the body only as far as the tyre can follow it, the spring's compression over a tick, and the body pushes the chassis back no harder than that. Along the ground, the drive, brake and grip push the body as far as its own movement was counted when they were sized: a car on its own wheels or a deck on ice takes the whole push and moves under it, while a crate the floor's friction holds passes it on to the floor. The fixed world carries whatever the body does not take. Drive conventions: positive `motorTorque` drives toward the parent body's local **-Z** (the engine's forward); positive `steerAngle` steers right. ## Fields | Field | Meaning | |---|---| | `suspensionDistance` | Suspension travel (m): the wheel hangs at most this far below the mount, and the spring compresses by at most this much from its rest, where the bump stop holds the wheel. | | `targetPosition` | Where the spring rests, as a share of `suspensionDistance` below the mount. The spring's rest length is `suspensionDistance * targetPosition`, and the wheel reaches the ground within that length plus its radius. 1 rests at full extension. The spring compresses from its rest by up to `suspensionDistance`, where the bump stop is. | | `springRate`, `damperRate` | Spring stiffness (N/m) and damping (N·s/m) per wheel. | | `maxSuspensionForce` | The most force (N) one wheel's suspension pushes with (default 6000). Raise it for a vehicle heavier than about 2 t on four wheels. | | `bumpStopRecovery`, `bumpStopSpeed` | How the bump stop pushes a chassis standing past it back out: by `bumpStopRecovery` of the depth each physics tick (default 0.2), and no faster than `bumpStopSpeed` (m/s, default 1). | | `groundAngle` | The steepest surface the wheel stands on (degrees, default 45): the widest angle between a surface's normal and the suspension, pointing back up it. The ray reads past a steeper face to the ground beyond it. A wheel at 60 climbs a 50 degree face that a default wheel reads past (a rock crawler, a kart riding kerbs, a bogie on a ramp); one at 30 stands only on gentle ground. | | `radius`, `width` | Wheel size (m). An unset radius comes from the wheel entity's model bounds, or else from its visual's. The ray is cast from the centre of the tread, so a chassis leaning over flat ground meets it at the same points at any lean. It is cast from a shoulder instead when the ground under that shoulder stands more than 1 mm above the ground under the centre, so a kerb or a plank under one shoulder holds the wheel up, or when the centre finds no ground. | | `motorTorque` | Drive torque (N·m). A wheel with no `inertia` drives with `motorTorque / radius` newtons, up to `forwardFriction` times the load it carries; a wheel that spins on its own takes it on its axle (see Spin below). | | `maxDriveSpeed` | The tread speed (m/s, default 0) up to which `motorTorque` drives a wheel that spins on its own: below it the wheel takes the whole torque, and from it on only what holds its tread there, on the ground and in the air, the way a rev limit holds an engine. A reverse drive is held to it backward. 0 drives the wheel at any speed. It bounds what the drive does: a gripping tyre turns its wheel at the speed the road passes under it, so a car rolling faster than the top (down a hill, or its rear end lifting over a crest) turns its wheels faster than it while its drive puts nothing on them. A wheel with no `inertia` rolls at the road speed and its drive is held by its grip alone. | | `brakeTorque` | Brake torque (N·m). A wheel with no `inertia` brakes with up to `forwardFriction` times the load, while `motorTorque` is 0, and so does `rollingResistance`; a wheel that spins on its own takes it on its axle, beside the drive. A braked car stands still on any slope its brakes' grip holds, gravity included. | | `steerAngle` | Steering angle (degrees), positive steers right. At light throttle the car turns on the radius its geometry gives, the wheelbase over `tan(steerAngle)`, as long as the turn asks less of its tyres than their sideways grip (`sidewaysFriction`); driving the steered wheels hard tightens the turn and driving only the others widens it. | | `frictionSlip` | The tyre's combined grip limit (default 10.5): the drive, brake and side grip together reach at most the suspension load times this before the tyre slides sideways. Lower it (1 or less) for ice, a drift car or skids. | | `sideFrictionStiffness` | The tyre's cornering stiffness (default 1): how hard it pushes back across its contact for each radian its contact slips off the line it rolls along, as a share of `corneringStiffness` times the load it carries. A standing tyre holds its contact still across the ground, so a chassis leaning on its springs or tipping over turns about its tyres' contacts; a rolling one answers a steady push across it with a steady slip angle, about 6 degrees at its sideways grip at the defaults. | | `corneringStiffness` | The base cornering stiffness (default 10): the sideways force, per newton of load, per radian of slip angle, that `sideFrictionStiffness` scales. At 10 and a `sidewaysFriction` of 1 the tyre's grip across the road peaks at about 6 degrees of slip angle; at 25 at about 2.3 degrees (a stiff race tyre), at 5 at about 11 (a soft, balloon or off-road tyre). | | `forwardFriction` | Longitudinal grip coefficient (default 1): drive and brake force are held to this times the load the wheel carries. | | `inertia` | The wheel's moment of inertia about its axle (kg·m², default 0). Above 0 the wheel spins on its own (see Spin below); about half the wheel's mass times its radius squared, 1 to 2 for a car wheel. 0 rolls it at the road speed. | | `forwardFrictionStiffness` | Slip-ratio stiffness of a wheel that spins on its own (default 1): how hard its tyre pushes along the road per unit of slip ratio, as a share of 10 times the load it carries. At the defaults its force reaches its load at a slip ratio of 0.1. | | `slideGrip` | The share of its grip a tyre of a wheel that spins on its own keeps once it slides (default 0.75): up to its peak slip it grips with all of `forwardFriction` and `sidewaysFriction`, and from `slideSlip` times that slip on with this share of them. | | `slideSlip` | Where a tyre's grip curve has fallen off, for a wheel that spins on its own (default 2): the slip, as a multiple of its peak slip, at which its grip has fallen in a straight line from its peak to `slideGrip` of it. 1 lets go at once past the peak (a peaky tyre); 3 to 5 falls off gently and holds a slide. See Grip curve below. | | `loadSensitivity`, `referenceLoad` | Tyre load sensitivity (default 0): every grip coefficient and stiffness of the tyre is scaled by `(load / referenceLoad) ^ -loadSensitivity`, so its grip per newton falls as its load rises, and at `referenceLoad` (N, default 4000) it grips with its coefficients as stated. 0 grips in proportion to load; 0.1 to 0.3 is a road tyre. Held to 0..0.9. See Grip curve below. | | `sidewaysFriction` | Sideways grip coefficient (default 1): the force the tyre pushes back with as the chassis moves across its contact, in a turn or under a push from the side, reaches at most this times the load it carries, less what its drive or brake spends of it. A car turning harder than that slides wide: steered 10 degrees, a 2 t truck turns on the 19 m its steering gives at 5 m/s and slides wide on its wheels at 20 m/s. Gravity's pull across a slope is held by the tyre's combined grip, `frictionSlip`, so a truck standing across a slope stays where it stands until it tips. | | `rollingResistance` | Drag on a freely rolling wheel, times the load it carries. The ground under the tyre adds its own `rollingResistance` (see Ground below). | | `surfaceGrip` | How this tyre grips particular ground: `{ { surface = "ice", grip = 0.35 }, { surface = "loose", grip = 0.8 } }`. On a surface an entry names, by its name or one of its tags, the tyre grips with `grip` of its stated grip in place of the surface's `friction`: a studded tyre on ice, an off-road tread on gravel. The surface's own name is matched first, then its tags in their order. Empty by default. | | `is2D` | The wheel applies no sideways grip. | | `visual` | The wheel's visual: an entity, or its id (see below). | | `solid` | The wheel is a volume other bodies strike (default false): see Solid wheels below. | | `mass` | The wheel's mass (kg, default 20) as a body of its own once it comes off. | | `breakLoad` | The force (N) above which the wheel comes off its vehicle (default 0, never): see Wheels that come off below. | | `attached` | Whether the wheel is on its vehicle (default true). Set false to take it off, true to put it back on its mount. | | `detachReason` | Why the wheel came off: `"load"` or `"command"`; empty while it is on. | The suspension ends at a **bump stop**: once the spring has compressed by `suspensionDistance` from its rest, the wheel holds the chassis off the ground there like a solid contact. It stops the chassis closing on the ground within the tick, so a landing faster than the springs can take, or a chassis heavier than its springs carry, ends on the stops with the tyre on the ground rather than in it, and the chassis is not thrown back up. A chassis that stands past its stops (put there by a script, say) is eased back out by `bumpStopRecovery` of the depth each tick, at no more than `bumpStopSpeed` (1 m/s by default). The spring is applied as an impulse worked out from the state at the start of each tick. So that it cannot feed on itself, its rate is held, per tick, to what the chassis' mass **and its rotational inertia** integrate stably: a light chassis, or one whose pitch or roll inertia is small next to its wheelbase, gets less of a very stiff spring than authored. The damper is applied to the velocity the chassis ends the tick with, which is stable at any rate, so the authored `damperRate` always acts whole. A damper pulls a wheel down no harder than its spring pushes it. ## Ground A tyre's grip coefficients (`forwardFriction`, `sidewaysFriction`, `frictionSlip`) are stated for ground of friction 1. On a surface content defined (`Physics.defineSurface`), named by the collider under the tyre or painted on a `Terrain` under it, every one of them is scaled by the surface's `friction`, or by the tyre's own `surfaceGrip` entry for that surface; its stiffnesses are not, so on slippery ground the tyre reaches its lower peak at a smaller slip. The ground's `rollingResistance` adds to the tyre's own: the surface's, or the collider's own on a collider naming none. So one car on tarmac, gravel, grass and ice brakes, accelerates and corners differently with no script, wheel by wheel: a car with its left wheels on ice and its right on tarmac pulls right under the brake. Ground naming no defined surface leaves the tyre's grip coefficients as stated, whatever the collider's own `friction`. A surface defined without a `friction` takes 0.5, so a tyre grips it with half its stated grip: state `friction = 1` for ground a tyre grips as stated (dry tarmac), and lower for looser ground, for example `Physics.defineSurface("tarmac", { friction = 1.0, rollingResistance = 0.01 })`, `"gravel"` 0.6, `"grass"` 0.45, `"ice"` 0.1. `surface` and `ground` in the runtime state name what each tyre stands on, and `Physics.tyreCurve(wheelId, { surface = "gravel" })` measures the curve on a given surface. ## Runtime state Read-only, updated every physics tick, and readable through `Physics.getWheelState(wheelId)`: - `isGrounded`: the tyre touches the ground anywhere within the suspension's full travel, `suspensionDistance` below the mount. Past the spring's rest it carries no load. - `compression` (0 with the spring at or past its rest length, up to `suspensionDistance`, where the bump stop is). - `angularVelocity` (rad/s) and `rotation` (rad): the wheel's spin and its angle about the axle, both growing as it rolls forward. A wheel with no `inertia` turns by the distance rolled over the radius; one that spins on its own turns at its own spin. - `skid` (m/s): how fast the tyre slides while its grip is used up; 0 while the tyre holds. Sideways for a wheel with no `inertia`; along the road too for one that spins on its own, so a locked or spinning tyre reads its slide. - `slipRatio`: the tread's speed less the road's under it, both positive rolling forward, as a share of the road speed (taken as at least 0.5 m/s), so its sign is the way the tyre pushes the car along the road. Rolling forward it reads 0 rolling, above 0 in wheelspin (1 at twice the road speed) and -1 locked; rolling backward the signs turn over, a wheel spinning backward past the road reading below 0 and a locked one 1. 0 for a wheel with no `inertia`. - `slipAngle` (degrees): the angle between the line the tyre rolls along and the way its contact moves over the ground, positive as the contact moves toward the wheel's right: how far into a drift the tyre is. - `roadSpeed` (m/s): how fast the ground passes under the tyre along the line it rolls along, positive rolling forward. `load` (N): the force the tyre presses the ground with, which its grip is sized by. - `sideImpulse`, `forwardImpulse` (N·s): what the tyre applied to the chassis this tick, and `sideForce`, `forwardForce` (N) the same over the tick. `suspensionForce` (N). `stopImpulse` (N·s): what the bump stop applied this tick, the part of a landing or a load the suspension could not take. - `center`, `hitPoint`, `hitNormal`: the wheel centre and the ground contact, in world space. A wheel with no ground within its travel hangs at full travel. - `surface`: the surface the tyre touches (`Physics.defineSurface`), the one the collider under it names there or, on a painted `Terrain`, the layer under the contact; absent on ground naming none. `ground`: the entity id of what it touches. Both are also on the component (`wheel.component.get("WheelCollider").surface`). - `reaction` (N): the force the ground and whatever struck the wheel's volume put on the wheel in the last tick: the suspension's push, the bump stop's, the tyre's along and across the road, and the contacts on its volume, their push and their friction, added as vectors. What `breakLoad` is measured against. `detachLoad` (N): the `reaction` the wheel came off at, 0 for one taken off by command. - `vehicleOrder`: the wheel's place among the wheels of its vehicle, from 1: the order the vehicle steps them in, which is the order they arrived in the world, and the order `Physics.vehicleState` lists them in. A wheel that came off keeps the place it last held; one that has not stepped on a vehicle reads 0. **Drivetrains.** An engine, a clutch, a gearbox and a differential driving the wheels are a `ShaftNetwork` (on the chassis, say) whose parts name the wheels: `{ name = "rearLeft", wheel = rl }`. A wheel a network drives spins on its own (with its own `inertia`, or the part's when it states none), its `motorTorque` (up to `maxDriveSpeed`) and `brakeTorque` still acting on its axle, and the network's links (a shaft, a gear ratio, a clutch, an open, locked or limited-slip differential) are solved with the tyres and the chassis in one step: one wheel on ice spins behind an open differential while the other stands, and a locked one drives both. The `ShaftNetwork` component README has the fields, and the physics guide (`topics/physics`) a car recipe. A driver for the wheels is built in: `VehicleController` on the chassis reads the vehicle input map, or the intent code gives it through `setIntent` (an AI driver, a replay, a test), and writes `motorTorque`, `brakeTorque` and `steerAngle`. `Physics.vehicleState(chassisId)` reads the whole vehicle: the chassis' forward speed (m/s, negative in reverse), how many wheels are grounded, and each wheel's state, in the order the vehicle steps its wheels. That order is the order the wheels arrived in the world (the first spawned first), and each wheel's place in it is its `vehicleOrder` (from 1). The vehicle steps its wheels in that order on every run and every engine, whatever entity slots the wheels were given, so a car stepped the same steps from the same state reads the same `Physics.stateDigest`. ## Spin: wheelspin, lock-up and drifts A wheel with an `inertia` above 0 spins on its own. Its spin is integrated each tick from the torques on its axle: `motorTorque` drives it, `brakeTorque` (with `rollingResistance` times its load) holds it toward still, and its tyre pushes back. The tyre pushes the chassis along the road in proportion to the slip between its tread and the road (the slip ratio, `forwardFrictionStiffness`), up to `forwardFriction` times its load; the wheel and the chassis are solved together, so it is stable at the engine's 30 Hz and 60 Hz ticks with a wheel however light. So: - **Wheelspin.** A drive torque past what the tyre puts down spins the wheel up faster than the road (`slipRatio` above 0), and the car gains speed only as fast as its grip pushes it: 250 N·m on each wheel of a 600 kg car (`inertia = 1.2`, radius 0.35) spins its wheels to more than twice the road speed on ice (`forwardFriction = 0.15`) and the car gains 2.2 m/s in 2 s, while on asphalt it pulls away with a slip ratio under 0.09 and reaches 8.6 m/s. The drive spins the wheel up to `maxDriveSpeed` at its tread and holds it there, the way a rev limit holds an engine: the same car with `maxDriveSpeed = 25` and 1500 N·m on each rear wheel spins its rear treads to 25 m/s from rest on asphalt and in the air and no faster, and still spins them past twice the road speed pulling away on `forwardFriction = 0.15`. `VehicleController` sets it from its `topSpeed`. With `maxDriveSpeed` 0 `motorTorque` acts whatever the wheel's spin, so a wheel driven past its grip keeps spinning up until the drive eases. `VehicleController`'s `tractionControl` eases it: it holds each driven wheel's drive to what its tyre pushes back with just short of the slip its grip peaks at, read from `Physics.tyreCurve`; a driver of your own does the same by cutting `motorTorque` while `slipRatio` stands past a target (0.1 to 0.5) the way the drive turns the wheel. - **Lock-up.** A brake torque past what the tyre holds stops the wheel (`angularVelocity` 0, `slipRatio` -1) while the chassis slides on, and a sliding tyre grips with `slideGrip` of its grip. The same car braked from 20 m/s stops in 26.9 m with every wheel locked (20000 N·m), and in 22.5 m with each brake held at 0.95 of what its tyre holds at the `load` it reads. A locked tyre holds only `slideGrip` of its grip, so a brake held at the peak keeps it locked: anti-lock braking is a driver that eases `brakeTorque` off while `slipRatio` stands past about 0.15 against the way the car rolls (below -0.15 rolling forward), letting the wheel roll again. - **Drift.** A tyre's grip along the road and across it is one grip: a tyre slid past its peak, spinning or locked, pushes against its slip in both directions with `slideGrip` of it, so the rear wheels of a car locked on the handbrake, or spun up under power, let go across the road and the car rotates into a drift (`slipAngle` on the rear tyres). Throttle and counter-steer hold it: from 15 m/s, the rear pair locked on 6000 N·m with the front steered 20 degrees for 0.7 s turns the car 32 degrees across its path, and 450 N·m on the rear with the front steered along the way the car moves holds it past 10 degrees for 1.6 s; a rear-driven car kicked into a slide at 10 m/s holds it past 10 degrees for 2.6 s with its throttle cut while the rear slip ratio stands above 0.5. Holding the throttle with the rear wheels spinning far past that leaves them next to no grip across the road, and the car spins. `VehicleController`'s `counterSteer` gives a car that counter-steer from the controller: it steers the front wheels along the way the car moves as it slides, so a car driven from keys that steer full lock or none holds a drift on the throttle and the steering keys (the `VehicleController` README, "Holding a slide"). A wheel in the air keeps its spin, turned by its drive up to `maxDriveSpeed` and slowed by its brake. A chassis lying still with its wheels spinning in the air (on its roof, say) falls asleep like any other body, and its wheels spin on from where they were when it wakes. A wheel with no `inertia` (the default) rolls at the road speed. ## Grip curve: peak, fall-off and load sensitivity A tyre's grip is a curve over its slip (a tyre or tire curve, or grip curve). Along the road its force rises with the slip ratio at `forwardFrictionStiffness` times 10 per newton of load, and across it with the slip angle (its tangent) at `sideFrictionStiffness` times `corneringStiffness` per newton, each up to its peak: `forwardFriction` and `sidewaysFriction` times the load. The two directions share one grip, an ellipse their two peaks span, so a tyre braking or driving hard has less left for cornering. On a wheel that spins on its own, past the peak the grip falls in a straight line to `slideGrip` of it at `slideSlip` times the peak slip and stays there, the tyre pushing against its slip; a wheel with no `inertia` grips up to its peak across the road and holds it there. A `loadSensitivity` above 0 makes the tyre grip with less per newton the more it carries, every grip and stiffness scaled by `(load / referenceLoad) ^ -loadSensitivity`: a heavy vehicle grips with less per kilogram than a light one on the same tyres, and a wheel loaded by weight transfer (the outside wheels in a corner, the front ones under braking) gains less grip than the load it takes, so a car's balance moves with its load. The whole force is held to `frictionSlip` times the load as well. So a tyre is stated by its peak (`forwardFriction`, `sidewaysFriction`), where it peaks (the stiffnesses), how it falls off (`slideGrip`, `slideSlip`) and how it takes load (`loadSensitivity`, `referenceLoad`): a peaky sim tyre, a forgiving drift tyre, a kart's, a truck's, a tyre on ice or on gravel. `@builtin::modules.tyres` holds presets of these fields (`road`, `grippy`, `peaky`, `drift`, `loose`, `ice`, `heavy`), as content, and any curve the fields state is one the engine takes: ```luau local Tyres = require("@builtin::modules.tyres") wheel.component.add("WheelCollider", Tyres.with("drift", { radius = 0.35, inertia = 1.2 })) ``` `Physics.tyreCurve(wheelId, opts?)` (the `phys.tyreCurve` tool) measures the curve a wheel states: its force against slip angle and, for a wheel that spins on its own, against slip ratio, at each load asked for, with each sweep's `peak` and `slide` and `gripScale`, the share of its stated grip it has per newton at that load. It is the force the wheel's solve settles on at that slip, so a tune can be checked by numbers before it is driven. Measured on a 600 kg car on four wheels that spin on their own (`inertia = 1.2`, radius 0.35), at the engine's 30 Hz and 60 Hz ticks. A grippy curve (peak 1.2, falling to 0.9 of it by 3 peaks) corners at 11.0 to 11.1 m/s² on a skidpad, reaches 17.5 m/s after 2 s of 600 N·m on each wheel and stops from 20 m/s in 18 to 18.5 m with every wheel locked; the default curve (1, falling to 0.75 by 2) corners at 8.2 to 8.6 m/s², reaches 14.7 m/s and stops in 26.2 to 26.7 m; a peaky curve (1.2, falling to 0.5 by 1.2) corners at 7.5 to 8.5 m/s², reaches 12.0 m/s and stops in 32.5 to 33.3 m, and a handbrake turn from 15 m/s swings it 32 degrees across its path before counter-steer straightens it out; a slidey curve (0.8, falling to 0.4 by 1.5) corners at 5.1 to 5.6 m/s², reaches 6.4 m/s, is still sliding 6 s into the stop, and ends the same handbrake turn still 12 degrees across its path. With a `loadSensitivity` of 0.3 the car at 1200 kg (springs, dampers and `maxSuspensionForce` doubled) corners at 0.82 of the 600 kg car's peak, against the stated `2 ^ -0.3` = 0.81, and at 0 at the same one; with 0.5 and `referenceLoad` at its wheels' static load, weight transfer onto the outside wheels lowers its skidpad peak by 2.3 to 2.6%. ## Solid wheels A wheel's suspension is a ray, so on its own a wheel has no volume: a post, a wall or another car meets the chassis' collider and passes through the tyre. A `solid` wheel carries a volume as well, riding with the wheel centre as the suspension travels and steering with it: the wheel entity's own collider when it has one that is not a trigger (a `SphereCollider`, or a `MeshCollider` hull of a tyre model on the wheel entity), else a cylinder of the wheel's `radius` and `width` about its axle. Walls, posts and other bodies strike it on its tread and on its faces, the contact holds the chassis back as a contact on the chassis' own collider does, and contact events name the wheel entity (`otherCollider`). Its contacts low on its tread, in the cap under the wheel centre that `groundAngle` spans (below the centre by the radius times the cosine of the angle), are the suspension's: the ground, a ramp, a kerb or a plank met there is mounted by the suspension as a ray-only wheel mounts it, and a car on solid wheels settles and drives as the same car on ray-only wheels does. With the default 45 degrees a wheel of radius 0.35 m mounts a kerb up to 10 cm high and strikes anything taller. The cylinder adds no mass to the chassis and takes the collision groups of the chassis' colliders; a collider of the wheel's own keeps its own. A trigger on the wheel entity stays a trigger beside the volume, standing where the wheel entity stands on the chassis. ## Wheels that come off A wheel comes off its vehicle when its `reaction` passes its `breakLoad`, or when `attached` is set false (`Physics.detachWheel(wheel)`). It leaves as a dynamic body of its own, on the wheel entity, with its `mass` and with the wheel entity's own collider as its collider, whenever it is taken off and whether or not it is `solid`: that collider leaves the chassis with it, and the chassis' mass, centre of mass and inertia are worked out again over the colliders it keeps. A wheel with no collider of its own, or whose own collider is a trigger, leaves on a cylinder of its `radius` and `width`, and a trigger of its own leaves the chassis with it on its body and goes back to its mount with it. It rolls, bounces and lies down like any body, and `Physics.getVelocity`, `Physics.applyImpulse` and the contact listeners reach it. The wheel entity stays under the chassis in the hierarchy, standing where its own body is, and its visual follows that body. The vehicle drives on the wheels it has left, the others keeping their suspension, spin and tyre state, and a `ShaftNetwork` part naming the wheel turns on its own (its `problem` says the wheel came off) until it goes back on. The mount is a fuse: a wheel torn off by its `breakLoad` passes its chassis no more than that over the tick it breaks in, of the blow's push and of the turn it gives the car alike. The wheel leaves moving as the blow left it, and the chassis keeps the rest of its momentum, so a car whose front wheel strikes a post carries on past it on its other wheels while the wheel stays at the post. Carrying on along its line, the car brings the wheel behind the torn one to the same post: a `breakLoad` that wheel's glancing blow stays under keeps it on, and a lower one sheds it too. A wheel taken off by command leaves moving as its chassis moved where it stood, spinning as it spun. `reaction` is a force over one physics tick. A 600 kg car on four wheels reads about 1.5 to 2 kN per wheel at rest and about 1.9 kN rolling over an 8 cm kerb at 15 m/s; striking a post at 15 m/s with one solid wheel reads about 285 kN at a 30 Hz tick and 570 kN at 60 Hz (the same blow over half the time). A `breakLoad` of a few tens of kN keeps wheels on through kerbs, jumps and landings and loses them to a crash. Set `attached` true again (`Physics.attachWheel(wheel)`) and the wheel goes back on its mount: its own body goes, and the vehicle drives on it from the next physics tick. `Physics.vehicleState(chassis)` lists the wheels on the vehicle under `wheels` and those that came off under `detachedWheels`, each with its `detachReason` and `detachLoad`. `attached` and `detachReason` are synced fields: on a shared world the peer simulating the vehicle breaks its wheels, every peer takes the wheel off, and the wheel's body moves on every other peer as the simulating peer moves it. ## Seeing the suspension `capture { pass = "physics" }` and the edit-mode collider overlay draw every wheel over the colliders: its suspension ray over its whole reach, `suspensionDistance` and the radius below the mount (green on ground, red in the air, as `isGrounded` reads), the travel from the mount to the tyre's centre coloured by how much of it is taken up (blue extended, yellow half way, red bottomed out), the tyre's radius as a white circle across its steered axle, and where the tyre meets the ground (yellow) with the ground's normal (cyan). `Physics.debugLines({ layers = { "wheels" }, entities = { chassis } })` returns those lines with each wheel's `grounded` and `compression` (the same values as `isGrounded` and `compression` here), `travel`, `suspensionLength`, `restLength`, `radius`, `mount` and `contactPoint` / `contactNormal`. In edit mode the vehicle stands at rest, so its wheels draw where they are mounted and follow their authored fields as they change. ## Visuals The wheel entity's transform is the suspension mount, so it stays where it is authored. Put the tyre mesh on another entity under the chassis (a child of the wheel is the usual place) and name it in `visual`, as the entity or its id (a prefab or player clone of the car points it at its own copy of the tyre): every tick the wheel places that entity at the wheel centre, turns it by the steering angle and spins it about the axle, starting from the rotation it had when the wheel first posed it. Methods: `setMotor(torque)`, `setBrake(torque)`, `setSteer(angle)`. ```luau local car = entity.spawn("car") car.position = { 0, 1, 0 } car.component.add("Physics", { kind = "dynamic", mass = 600 }) car.component.add("BoxCollider", { half = { 0.9, 0.3, 2.0 } }) for _, at in { { -0.85, -1.3 }, { 0.85, -1.3 }, { -0.85, 1.3 }, { 0.85, 1.3 } } do local wheel = entity.spawn("wheel", { parent = car.id }) wheel.localPosition = { at[1], -0.3, at[2] } local tyre = entity.spawn("tyre", { parent = wheel.id }) tyre.component.add("Model", { model = "cylinder" }) tyre.localRotation = { 0, 0, 0.7071068, 0.7071068 } -- the cylinder's axis along X tyre.localScale = { 0.7, 0.25, 0.7 } wheel.component.add("WheelCollider", { suspensionDistance = 0.3, springRate = 20000, damperRate = 2000, visual = tyre, }) end ```

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

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

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

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

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

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

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