atmosphere

# HeightFog The scene's atmosphere, as a component. Add it to an entity and the scene gets exponential height fog: density thins with altitude, so a valley pools fog while a hilltop above it clears, and the medium brightens toward the sun. ```lua local id = entity.spawn("atmosphere").id entity(id).component.add("HeightFog", { density = 0.03, heightFalloff = 0.12, heightRef = 0, inscatter = 2.5, }) ``` Every field is live — editing one in the inspector moves the fog on the next frame, and the values persist with the scene. Setting `density` to 0 turns fog off while keeping the rest of the settings authored; removing the last one in the scene clears it entirely. | field | effect | |---|---| | `color` | The colour a fully fogged surface reaches, and so the colour of the far field. Defaults to `(0.62, 0.68, 0.78)`, a daylight grey. | | `density` | Extinction per world unit at `heightRef`. 0 is no fog. | | `heightFalloff` | Thinning with altitude, per world unit. 0 gives a distance-only fog. | | `heightRef` | The world-space Y that `density` describes. | | `start` | Distance before fog accumulates, so near geometry stays readable. | | `inscatter` | How far the medium goes toward `sunColor` at the centre of the sun, in [0, 1]. 0 makes fog directionless. | | `sunColor` | The colour fog takes on when looking into the sun. | | `inscatterAnisotropy` | Forward-scattering bias in [0, 0.95). Higher tightens the lobe. | The sun the lobe points at is the scene's own, re-read each frame, so fog follows a day/night cycle without being told. Code that changes fog at runtime can drive the same settings through `@builtin::systems.atmosphere.fog` instead.

# PhysicalAtmosphere The air the scene is seen through, as a component. ```lua local id = entity.spawn("atmosphere").id entity(id).component.add("PhysicalAtmosphere", { aerial = 1.0, -- how much of the result reaches the image sky = true, -- the visible sky comes from the same scattering worldUnitsPerKm = 1000, -- 1 world unit is a metre }) ``` Distance starts costing contrast and saturation the way it does outdoors: a ridge kilometres away shifts toward the sky's colour instead of rendering at full contrast as though it were metres away. With `sky` on, the visible sky comes out of the same scattering integral as the air in front of the geometry, so the two agree at the horizon by construction and the sky's colour follows the sun's elevation — sunrise, midday and dusk with no per-time-of-day authoring. Every field is live: edit one in the inspector and the atmosphere follows. Setting `aerial` to 0 with `sky` off turns it all off without losing the rest of the settings. `worldUnitsPerKm` is the field to get right first. Scattering is computed in kilometres against Earth's coefficients, so this is what maps the scene onto real atmospheric distances — set it too low and a courtyard fogs like a valley. The sun's direction and brightness are read from the scene's own directional light, so a day cycle needs nothing on this component to move. `groundAlbedo` and `sunColor` are the two fields that give the scattering a hue. `groundAlbedo` is the reflectance of the ground the sky is lit over and feeds the multiple-scattering term, so a warm ground carries its colour up into the air; `sunColor` tints the light entering the atmosphere, colouring the sky and the aerial perspective together. The rest of the fields move the sky between Earth's blue and a neutral grey. ```lua entity(id).component.add("PhysicalAtmosphere", { sky = true, groundAlbedo = { 0.68, 0.44, 0.23 }, -- warm dust underfoot sunColor = { 1.0, 0.60, 0.30 }, -- and a low ochre sun }) ``` For code that adjusts the atmosphere at runtime, reach for `@builtin::systems.atmosphere.atmosphere` — same options, no component. The full description of what each knob does and how the passes work is in the package readme: `guides { path = "systems/atmosphere" }`.

# aerialPerspective The render feature behind `PhysicalAtmosphere` and `@builtin::systems.atmosphere.atmosphere`. Four compute passes run after lighting, in order: | order | pass | output | |---|---|---| | 10 | `atmo_transmittance` | 256x64 transmittance from a point out to the top of the atmosphere, in the Bruneton (r, mu) parameterisation | | 12 | `atmo_multiscatter` | 32x32 multiple-scattering transfer function, integrated over the sphere of directions | | 14 | `atmo_skyview` | 192x108 sky radiance per view direction from the camera's altitude, horizon-concentrated | | 16 | `atmo_composite` | scene depth in, aerial perspective and sky out | The composite reconstructs each pixel's world position from `@scene.depth` and the drawn camera's inverse view-projection (`@frame.camera`), marches the medium between the camera and the surface, and applies `surface * transmittance + in-scattering`. Sky pixels sample the sky-view LUT and add the solar disc, attenuated by the same transmittance — which is what reddens a low sun. Because the camera comes from `@frame.camera`, the atmosphere is correct in offscreen captures and render-to-texture cameras, not only the live viewport. The sky-view LUT derives its own altitude and sun elevation from that same camera, so a capture from a different viewpoint gets its own sky rather than the live viewport's. Sky and geometry come out of one integral, so they agree at the horizon by construction: as a surface recedes its transmittance goes to zero and its in-scattered term goes to exactly the sky radiance for that direction. Scattering coefficients are Earth's, in kilometres and inverse kilometres. `worldUnitsPerKm` maps the scene onto them, so the same physics serves a metre-scale scene and a kilometre-scale one. ## Costs The three LUTs are rebuilt every frame. Together they are around 1.2M shader steps — under a single full-screen pass at 1080p — and rebuilding unconditionally is what lets the sun move continuously with nothing to invalidate. The composite marches per pixel rather than sampling a low-resolution froxel volume. That trades the volume's fixed cost for accuracy that does not depend on where a surface falls between froxel slices; `aerialSteps` is the knob. ## Colour The scene target holds display-encoded values, so the composite decodes them to linear, attenuates and adds in-scattering in radiance, and encodes the result. `exposure` is what maps radiance into the displayable range — raise it for a brighter sky, and the aerial perspective brightens with it, since both come from the same integral. Parameters arrive through the `atmo_params` buffer, packed by `@builtin::systems.atmosphere.atmosphere`.

# atmo_common The atmosphere's shared ground: the medium's Rayleigh and Mie coefficients, the phase functions, the planet geometry, and the ray-sphere intersections every atmosphere pass needs. Included by the atmosphere passes with `#include "@builtin::systems.atmosphere.atmo_common"`.

# atmo_composite Applies the atmosphere to the rendered scene: sky where nothing was drawn, and aerial perspective over what was. ## Includes - `atmo_common` - `atmo_transmittance_lookup` - `atmo_multiscatter_lookup` - `atmo_integrator` ## Bindings | name | kind | |------|------| | `scene_color` | `texture2d` | | `scene_depth` | `texture_depth` | | `frame_cam` | `buffer` | | `atmo_params` | `buffer` | | `transmittance_lut` | `texture2d` | | `multiscatter_lut` | `texture2d` | | `skyview_lut` | `texture2d` | | `atmo_out` | `storage2d (rgba16f)` | `atmo_out` holds linear light, which sun and sky radiance can carry past 1.0 — an 8-bit target would clamp it.

# atmo_integrator Marches a ray through the medium, accumulating in-scattered light and attenuating by transmittance at each step. Included by the atmosphere passes with `#include "@builtin::systems.atmosphere.atmo_integrator"`.

# atmo_multiscatter Bakes the multiple-scattering table by integrating light over every direction at a point, so later passes read one sample instead of re-marching. ## Includes - `atmo_common` - `atmo_transmittance_lookup` ## Bindings | name | kind | |------|------| | `atmo_params` | `buffer` | | `transmittance_lut` | `texture2d` | | `multiscatter_out` | `storage2d (rgba16f)` |

# atmo_multiscatter_lookup Reads the multiple-scattering table: the light that reaches a point after bouncing more than once, which is what keeps a sky from going black away from the sun. Included by the atmosphere passes with `#include "@builtin::systems.atmosphere.atmo_multiscatter_lookup"`.

# atmo_skyview Bakes the sky as seen from the camera's height into a lat-long table, so the composite reads a direction instead of marching one. ## Includes - `atmo_common` - `atmo_transmittance_lookup` - `atmo_multiscatter_lookup` - `atmo_integrator` ## Bindings | name | kind | |------|------| | `atmo_params` | `buffer` | | `frame_cam` | `buffer` | | `transmittance_lut` | `texture2d` | | `multiscatter_lut` | `texture2d` | | `skyview_out` | `storage2d (rgba16f)` |

# atmo_transmittance Bakes the transmittance table: for a height and a sun angle, how much light survives the path out of the atmosphere. ## Includes - `atmo_common` ## Bindings | name | kind | |------|------| | `atmo_params` | `buffer` | | `transmittance_out` | `storage2d (rgba16f)` |

# atmo_transmittance_lookup Reads the transmittance table: how much light survives a path from a point to the sun, sampled rather than integrated. Included by the atmosphere passes with `#include "@builtin::systems.atmosphere.atmo_transmittance_lookup"`.

# atmosphere Physically-based atmospheric scattering — aerial perspective on distant geometry, and a sky whose colour follows from the sun's elevation. ```lua local atmosphere = require("@builtin::systems.atmosphere.atmosphere") atmosphere.set({ aerial = 1, sky = true, worldUnitsPerKm = 1000 }) atmosphere.get() --> the settings in force atmosphere.active() --> are the scattering passes running atmosphere.clear() --> off, settings kept for the next set() ``` `set` takes any subset — omitted fields keep their current value, so adjusting one knob does not mean restating the rest. With `aerial` at 0 and `sky` off nothing is wanted and the passes are released rather than run at zero strength. `worldUnitsPerKm` is the one number that has to match the scene. Scattering is computed in kilometres against Earth's coefficients, so it is what maps a scene onto real atmospheric distance. At the default 1000 a world unit is a metre. `sunDirection` / `sunIntensity` follow the scene's sun unless the call pins them. Sun elevation is what drives the entire appearance of a physical sky, so that is what lets a day cycle reach the sky with nothing else authored. `sunColor` defaults to white on purpose: the warm colour of a low sun comes out of the transmittance through a longer air path, not out of a tint. For an atmosphere a scene should simply have, author the `PhysicalAtmosphere` component instead — it carries the same settings, persists with the scene, and edits live in the inspector. This module is for code that changes the atmosphere at runtime: a weather system, a cutscene, a quality slider. The full description of what each knob does and how the passes work is in the package readme: `guides { path = "systems/atmosphere" }`.

# fog Scene-wide exponential height fog with directional in-scattering. ```lua local fog = require("@builtin::systems.atmosphere.fog") fog.set({ density = 0.03, heightFalloff = 0.12, heightRef = 0, inscatter = 2.5 }) fog.get() --> the settings in force fog.active() --> is the fog pass running fog.clear() --> fog off, settings kept for the next set() ``` `set` takes any subset — omitted fields keep their current value, so adjusting one knob does not mean restating the rest. A `density` of 0 turns fog off and releases the render pass rather than running it at zero strength. `sunDirection` / `sunIntensity` follow the scene's sun unless the call pins them, which is what keeps in-scattering pointing the right way under a day/night cycle. For fog that a scene should simply have, author the `HeightFog` component instead — it carries the same settings, persists with the scene, and edits live in the inspector. This module is for code that changes fog at runtime: weather, cutscenes, a quality slider. The full description of what each knob does and how the pass works is in the package readme: `guides { path = "systems/atmosphere" }`.

# heightFog The render pass behind the `HeightFog` component and the `fog` module. One compute pass after lighting reconstructs each pixel's world position from `@scene.depth` and the drawn camera's inverse view-projection (`@frame.camera`), integrates the height-falloff density along the view ray analytically, and blends the surface toward the fog medium by the resulting transmittance. The in-scattering term is a Henyey-Greenstein lobe around the direction to the sun, normalised against the isotropic phase so the strength knob means the same thing at any anisotropy. Working in world space is what lets density vary with altitude and what lets the medium respond to view direction — neither is expressible from screen depth alone. Parameters arrive through the `heightfog_params` buffer, packed by the `fog` module. Sky pixels are passed through untouched. Because the camera rides `@frame.camera`, the fog is correct in offscreen captures and render-to-texture cameras at their own resolutions, not only in the live viewport.

# height_fog Fogs the scene by depth and by height, so the air thickens toward the ground and toward the horizon at once. ## Bindings | name | kind | |------|------| | `scene_color` | `texture2d` | | `scene_depth` | `texture_depth` | | `frame_cam` | `buffer, read vec4<f32>` | | `heightfog_params` | `buffer, read vec4<f32>` | | `fog_out` | `storage2d (rgba16f)` |

# Package (asset type) A package is an asset — a `<Name>.package/` folder that bundles components, modules, scenes, presets, tools, and any other typed sub-assets under one identity, installed into a world as one unit. Packages are how authoring sets get distributed across worlds. A **library** is the addressable root scope content resolves under (`@builtin`, `@<name>`) — a whole world mounted into this one under a namespace, via `zeromind.installLib` / `world.installLibrary`. A package is an asset that lives inside such a root, and one library holds as many packages as its author put there. A package is installed by guid the way every asset is (`zeromind.installAsset`). ## When to use one - You're authoring a coherent feature suite (character controller stack, voxel engine, UI kit, animation library) and want to ship it as one install target. - You want a stable identity worlds can install and resolve sub-assets against (`@<lib>::pkg.sub_module`). - You want versioning + a per-package metadata layer that travels with the contents. If you're authoring inside a single world and don't need a separate install lifecycle, you don't need a package — drop your `.component` / `.module` / etc. directly in `/zero/source/`. Packages are for cross-world distribution. ## Where it lives - Source: `/zero/source/.../<Name>.package/` (or, for legacy packages, a folder containing `package.yaml` at its root). - Identity: `<Name>` (the `.package` suffix collapses in identity — mirrors `.module`). A file at `<Name>.package/<sub>/init.luau` resolves under the same identity it would at `<Name>/<sub>/init.luau`. - Folder shape (container-style — open child set): - `package.yaml`: metadata (name, version, description) and the packages it depends on (`dependencies`). **Required.** - `README.md` — instance documentation. **Required.** - `.metadata` — agent-editable tags + free-form fields. **Required.** - Sub-asset folders: any combination of `.component/`, `.module/`, `.scene/`, `.preset/`, `.tool/`, `.toolbox/`, `.material/`, `.shader/`, etc. The validator permits unlisted children (`allow_unlisted: true`) by design — packages are open containers. ## How to create one ```luau asset.create("package", "<Name>") -- Creates: /zero/source/<Name>.package/ -- package.yaml (metadata scaffold) -- README.md (instance README template) -- `folder` places it in a subfolder of /source instead of the root: asset.create("package", "<Name>", { folder = "systems" }) ``` Then scaffold sub-assets inside it: ```luau local pkg = asset.resolve("<Name>.package") asset.create("component", "Spinner", { into = pkg }) asset.create("module", "util", { into = pkg }) ``` ## `package.yaml` ```yaml name: inkBlocks # optional; the folder stem when absent version: "1.0.3" description: "Ink and paper style blocks" dependencies: - { name: starterBlocks, version: "1.0.8" } - styleKit # a bare name states no version ``` `dependencies` lists the packages this package needs. Each entry's `name` is a reference the package records, the same kind of reference a `require` or an asset name in a data file makes: - **It resolves in the author's world.** Install the dependency here first (`zeromind.installAsset`); the entry then names the copy this world holds. A push refuses a package whose dependency resolves to nothing, naming it. - **An install brings it along.** Installing the package installs every dependency it lists, at the version this world holds when the package is pushed, under `/source/deps/<owner world>/`, deduplicated against what the installing world already holds. `zeromind.preview` lists each one before anything is written, and the install's `deps` lists what it brought. Uninstalling the package leaves a dependency that another installed package still uses. - **`version` is checked, not chosen.** A stated `version` has to equal the `version` the dependency's own `package.yaml` states in this world; `asset.validate` (and so the push) refuses the package naming both when they differ. To depend on another version, install that version here. ## How it operates 1. **Registration.** Writing `package.yaml` indexes the package with the package registry. 2. **Install.** A package is read before it is installed: `zm ls-tree @<guid>` in the shell lists what it contains, and `zm show @<guid>:<path>` and `zm grep <pattern> @<guid>` read it, so candidates are compared by what they do. The one that fits is installed by guid, the way every asset is: `zeromind_install` over the engine's MCP, or `tools.use("zeromind", "installAsset", <guid>)` inside the engine. The install writes the package's files (and the deps its `.refs` record, the packages its `package.yaml` lists under `dependencies` included) into this world's source, so its sub-assets resolve here. `tools.use("zeromind", "preview", <guid>)` reports what an install would write before it writes anything. 3. **Sub-asset resolution.** Because `.package` collapses in identity, sub-asset paths work whether the package folder is suffixed (`<Name>.package/<sub>`) or not (`<Name>/<sub>`). 4. **Updates.** `tools.use("zeromind", "updates")` lists installed content with upstream changes available; re-running the install pulls them. 5. **Metadata.** `package.yaml::name` overrides the folder stem if present (rare); `version` + `description` are surfaced in the package index. 6. **Hot reload.** Edits to sub-assets hot-reload as normal; edits to `package.yaml` reload package metadata. ## Discovery - `asset.list("package")` — every registered package. - `asset.inspect("<name>")` — sub-asset catalog, source, this type README. - `ls /zero/source/<Name>.package` lists the files the folder holds. - `library.list()` — the library assets registered in this world, including the ones packages under an installed library contribute. ## Authoring conventions - Name packages by their feature (`voxels`, `cameraRigs`, `dialogSystem`), not by their owner — the host library is the `@<lib>::` scope prefix. - Cluster cohesive sub-assets together. A "character controller" package should ship the controller component, its preset configs, its supporting modules, and a demo scene — not just the component. - Document the package's surface in `README.md` — what install installs, what each sub-asset does, how they relate. Agents reading `cat /zero/source/<Name>.package/README.md` get the full picture in one shot. - Version conservatively — breaking a package means breaking every world that installed it. Use semantic version bumps. ## Common pitfalls - **Missing `package.yaml`.** Without it the folder isn't recognized as a package even if it has a `.package/` suffix. - **A dependency named only by a string the code builds.** A package whose files reach another package only through a name assembled at runtime records no reference to it, so an install arrives without it. List that package under `dependencies` in `package.yaml`. - **Identity collapse.** Sub-asset paths skip the `.package` suffix. Don't include `.package` in `require` strings. ## Referencing inside a package: the `~` rule `~` means **this package**, resolved structurally from the referring file's own location. It is the only package-specific syntax. It is rename-safe (no package name is ever written) and library-agnostic (it never names the host library, so it survives `@builtin` being renamed or the package being mounted elsewhere). `~.tail` maps to `<pkg>.package/tail` from anywhere inside the package. | Referencing from | Use | Example | |---|---|---| | An asset/module **inside this package** | `~.tail` | `require("~.modules.myThing")`, `shader: "~.shaders.myThingBlend"` | | A **different package** under the same root | root-relative identity | `require("@root::systems.otherPkg.modules.x")` | | A **different library's** public API (a deliberate external dependency) | `@otherlib::…` | `require("@physics::modules.rigidbody")` | **Never write `@builtin::` (or any host-library name) to reference your own package** — that couples the package to the library it currently lives in and breaks if the library is renamed or the files move. Use `~.`. It works from Luau `require()` and from asset-reference strings in data files (a material's `mat.yaml` `shader:` field, a component's default asset ref); the engine resolves it against the referring file's own package. `asset.resolve` takes a `~.` name the same way, against the package of the file that calls it: `asset.resolve("~.materials.myThingStandard", "material")`. `~.` is the package-relative self-reference; `@root::` is the root-relative one (the library root, or the world source tree for non-library content). The `core/requiring-modules` guide covers the root model in full. A package that ships substantial functionality should include a `.guide` asset (a `<name>.guide/guide.md` folder anywhere under the package); the `guides` tool discovers it live, so collaborators find the system the way they find built-in guides. A package's test suite reaches the shared `Test` framework through its enclosing asset: `local Test = asset.containing(__FILE__).modules.shared` (`asset.containing` returns the deepest enclosing typed asset, the `.testSuite`, not the outer `.package`). ## Related types - Any of `.component`, `.module`, `.scene`, `.preset`, `.tool`, `.toolbox`, `.material`, `.shader`, `.style`, `.service`, `.importer` — packages bundle these. ## In the Inspector Package: the name, version and description package.yaml declares, how many things the package holds and what they are, and **Open** for package.yaml. A package.yaml that does not decode is listed under Problems with the decoder's error.

# 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`.

# renderFeature A **render feature** inserts custom GPU passes into the frame pipeline. The engine provides one generic capability — a per-frame render-pass queue and a set of pipeline-phase insertion points — and a feature is the authored Luau that decides what passes to enqueue, and where, every frame. ## Authoring contract A `.renderFeature` folder holds an `init.luau` that returns a feature module: ```luau return { setup = function(ctx) -- optional; runs once when the feature goes live -- A "fragment" pass's `shader` names a POST EFFECT, not a `.shader` -- guid directly — postprocess.add compiles the shader asset under -- that name once, here. Enqueueing a name never passed to -- postprocess.add runs the pass as a no-op every frame (the log -- reads "effect '<name>' not compiled — pass skipped"). postprocess.add("my_effect", asset.resolve("my.shader.guid", "shader"), { enabled = false }) end, render = function(ctx) -- required; runs every frame -- enqueue one or more passes. The spec shape depends on `kind` (see -- "Pass kinds" below): this is a "fragment" pass (full-screen shader over -- input textures); a mesh effect (outline, x-ray) is a "geometry" pass -- with `material` + `select` (see "Geometry passes"). ctx.enqueue { phase = "afterTransparent", shader = "my_effect", inputs = { src = "@scene.color" }, output = myRenderTargetGuid, } end, teardown = function(ctx) end, -- optional; runs once when the feature is destroyed } ``` Optional `materials/` and `shaders/` subfolders hold shader source the feature constructs GPU programs from. A feature constructs its GPU programs (it does not reference `.material` surface assets). ## `ctx` Built fresh each frame and passed to `setup` / `render` / `teardown`: | Field | Meaning | |-------|---------| | `ctx.enqueue(spec)` | Queue one render pass for the current frame. | | `ctx.viewport` | `{ w, h }` — the **main viewport's** size in pixels. | | `ctx.time` | Seconds since boot. | | `ctx.frame` | Monotonic frame index. | | `ctx.renderPath` | `"forward"` / `"deferred"` / … — branch passes on the active path. | | `ctx.settings` | The feature's knobs as they stand this frame — see "Settings". | ## Settings A feature declares the knobs it takes as `settings`, each a Field descriptor with a default, the way a component declares its public fields: ```luau local Fields = require("@builtin::modules.field") local Field, NoSync = Fields.Field, Fields.NoSync return { settings = { intensity = Field.number(1.0, NoSync, "How much of the effect reaches the image."), quality = Field.enum({ "low", "high" }, "high", NoSync, "How many samples the pass spends."), }, render = function(ctx) local s = ctx.settings -- { intensity = 1.0, quality = "high" }, or what a caller set ... end, } ``` The engine holds one settings table per live feature — every declared default, overridden by what it was handed — and passes it as `ctx.settings` on every `setup` / `render` / `teardown`. A feature reads its knobs there and nowhere else, so any caller tunes any feature by name: ```luau local h = renderer.feature.create(ref, { settings = { intensity = 0.5 } }) renderer.feature.configure(h, { quality = "low" }) -- lays over the rest renderer.feature.settings(h) -- { intensity = 0.5, quality = "low" } renderer.feature.find(ref) -- the live handle, or nil renderer.feature.schema(ref) -- the declared knobs, unrun ``` A knob the feature does not declare, or a value of the wrong shape, is refused by name. A scene authors its features on one `RenderFeatures` entity — a list of features, each with its settings — which adopts a feature already live rather than stacking a second, and takes every one down on disable and destroy. `render` runs **once per frame**; the passes it enqueues run **once per render target** drawn that frame — the live viewport, every offscreen capture, every RTT camera — each at its own resolution. So `ctx.viewport` is the main viewport's size, not the size of the target a pass ends up drawing into. Size a full-screen scratch RT with `screen = true` and let the engine track the drawn target (see "Screen-sized targets") rather than deriving it from `ctx.viewport`. ## Screen-sized targets `renderer.texture.create { screen = true }` marks a feature RT as full-screen: before each render target's feature passes, the engine resizes it to that target's resolution. Create it once — the engine owns its size from then on: ```luau myRt = renderer.texture.create { width = ctx.viewport.w, height = ctx.viewport.h, -- initial size only screen = true, format = "rgba16f", name = "my_effect", } ``` A target that holds a picture of the scene is `rgba16f`, which is what the scene target itself carries: linear light with headroom above the display's white and no 256-step floor under a dark gradient. Omitting `format` on a screen-sized target asks for the same thing. `format = "rgba8"` is for a mask, a weight or an occlusion term, where 0..1 is the whole range — hand one of those back over `@scene.color` and the frame loses every highlight and bands every gradient, and the engine says so in the log. `screenScale` (default `1.0`) takes a fraction of the drawn target's resolution, for a scratch that runs below composite resolution (a half-res blur passes `0.5`). A screen-sized RT is what makes a full-screen effect composite correctly at any resolution. Deriving the size from `ctx.viewport` instead pins the RT to the main viewport, and every differently-sized render target then composites a mismatched scratch — the scene scaled into a corner with the rest black. `screenSpace` names WHICH image a screen-sized RT follows: | value | what it tracks | |---|---| | `"scene"` (default) | the scene render target, at whatever resolution the render scale asked for. Resized before EVERY render target's feature phases — the main frame and each offscreen one — and cleared to transparent before an offscreen render, so one sink never reads what another left behind | | `"composite"` | the image the post-scene phases draw into. Resized on the presented frame only, and never cleared for an offscreen render, since none of those phases run there | The two carry the same size until the render scale drops below 1. From there, while the renderer presents the viewport itself, the scene reaches the display's resolution through an upscale that runs before `afterScenePost` — so a composite-space RT is the display's size while a scene-space one is the smaller rasterized frame. Under a UI viewport panel the panel draws the scene target at its own rect, nothing upscales beforehand, and both spaces carry the scene's size. A scene-space target is scratch: whatever a pass does not rewrite this render is transparent black. A composite-space target survives an offscreen render untouched, but it follows the presented frame alone. ## History targets An accumulation across frames (temporal antialiasing, a temporal denoiser, any pass that reads what it wrote last time) lives in a history target: ```luau history = renderer.texture.create { width = ctx.viewport.w, height = ctx.viewport.h, -- initial size only history = true, format = "rgba16f", name = "my_accum", } -- in render(ctx): ctx.enqueue { kind = "compute", program = myResolve, inputs = { scene_color = "@scene.color", accum_previous = history.previous.guid }, buffers = { accum_state = history.state }, storage = { accum_out = history.guid }, phase = "afterLighting", } ``` The passes a feature enqueues run once for every view the frame draws (the viewport, each render-to-texture camera, each capture), so an accumulation has to be one per view. A history target keeps one pair of images per view, sized to that view: for the length of a view's render `history.guid` names the image the render writes and `history.previous.guid` the image the same view's previous render wrote. Another view never resizes, clears or overwrites them, and a view's images are freed when it stops drawing. It follows `screenSpace` and `screenScale` like any screen-sized target; a composite-space one is kept for the viewport, the one view that draws the post-scene phases. Before each render of a view the engine writes `history.state`, one `vec4<f32>` a pass binds through `buffers`: | field | holds | |---|---| | `x` | 1 when `previous` holds this view's previous image; 0 on the view's first render, its first after a camera cut or a change of size, or after a render of the view that ran without the target, and `previous` then reads transparent black | | `y` | how many renders in a row have carried the history | | `zw` | this render's sub-pixel projection offset, in pixels (`renderer.setProjectionJitter`) | `renderer.setProjectionJitter` is the matching per-view sample sequence: every view walks it by its own count of renders, so the sequence a temporal pass expects is the one each view's renders sampled. ## Pass phases `enqueue` runs a pass at a named pipeline boundary — a real seam between the scene's discrete passes — ordered within a phase by `order`. Each phase is the point where the scene colour holds a specific, nameable state: | Phase | Scene colour there | |-------|--------------------| | `afterDepthPrepass` | the visibility raster written: `@scene.depth` holds this frame's complete opaque depth, and `@scene.motion` its opaque motion, before anything shades. Scene colour is not yet drawn; `@scene.colorHistory` holds the previous frame's lit colour, and the deferred g-buffer the previous frame's surfaces (`readsPrevious`) | | `afterShadows` | shadow maps populated; scene colour/depth not yet drawn | | `afterSky` | sky only; depth empty | | `afterOpaque` | opaque drawn, before transparents. `@scene.depth` (and the deferred G-buffer) are populated. Forward: lit opaque. Deferred: opaque is in the G-buffer, so the colour is still sky only until the composite (use `afterOpaqueLit`) | | `afterOpaqueLit` | the lit opaque scene, still before transparents, on **both** paths — the forward opaque draw, or the deferred lighting composite. The background a refractive or transmissive surface samples: the one phase whose colour holds what is behind such a surface without holding the surface itself | | `afterTransparent` | transparents drawn, before the OIT composite | | `afterLighting` | deferred-lighting + OIT composite done — fully lit, final geometry on **both** paths | | `afterScenePost` | scene-layer post (DoF/MB/…) done, before UI | | `afterUI` | scene + UI composited | | `afterPost` | all-layer post done — the final image, before present | The last three are the post-scene phases, and they work on the COMPOSITED image: `@scene.color` there is the target the UI lands on, not the scene render target. `@scene.depth` and `@scene.motion` still bind — they are the scene's own buffers for the frame just drawn, which is what lets a pass at these phases reproject the composite it is handed — but they keep the SCENE's resolution. Whenever the render scale is below 1 on the presented frame, that is smaller than `@scene.color`, so a pass here maps between the two by uv rather than by texel index, and takes its own output size from the target it writes. The `@scene.*` inputs (`@scene.color`, `@scene.depth`, …) bind the live frame buffers; the deferred g-buffer channels (`@scene.normal`, `@scene.shaded`, …) resolve only on the deferred path. Before the pass that shades has drawn — at `afterDepthPrepass` — a g-buffer channel holds the previous frame's surfaces, and a pass reading it there names the slot in `readsPrevious` (`readsPrevious = { "scene_normal" }`); one that does not is held back rather than handed a stale normal. `@scene.colorHistory` is the lit colour the target's previous render ended with, kept by the engine per render target and never cleared by a frame: what a pass tracing at `afterDepthPrepass`, against this frame's depth, takes its light from — reprojected through the previous view-projection `@frame.camera` carries. A capture drawn once, or a camera drawn again after a pause, is drawn lit first when a pass reads the history, so its first frame holds one. Every `@scene.*` channel, what it holds, its format, the phase it is first valid from, and the other names it answers to: | Name | Holds | Format | Valid from | Also named | |---|---|---|---|---| | `@scene.color` | the scene's lit colour; the display composite at a post-scene phase | the scene target's format at a scene phase, the display composite's at a post one | every phase | — | | `@scene.depth` | opaque depth, reversed (1.0 near, 0.0 far/empty sky) | `Depth32Float` — binds through a `texture_depth` compute slot, not `texture2d` | `afterDepthPrepass` on | — | | `@scene.motion` | screen-space NDC velocity since the previous frame | `Rg16Float` | `afterOpaque` on | — | | `@scene.normal` | world-space normal + the per-pixel surface-flag field | `Rgb10a2Unorm` | deferred path, `afterOpaque` on (previous frame's before — declare `readsPrevious`) | — | | `@scene.shaded` | what a surface SENT — its shaded colour, linear and scene-referred | `Rgba16Float` | deferred path, `afterOpaque` on (previous frame's before) | `@scene.albedo` | | `@scene.material` | what a surface IS — base colour (RGB565) + metallic + perceptual roughness | `Rgba8Uint` | deferred path, `afterOpaque` on (previous frame's before) | `@scene.mr` | | `@scene.emissive` | radiance a pass stamped on the surface, added at the composite | `Rgba16Float` | deferred path, `afterOpaque` on (previous frame's before) | — | | `@scene.ao` | scene occlusion a feature wrote, read back by shading | `Rgba8Unorm` | every scene phase (cleared at the top of the scene render) | — | | `@scene.reflection` | traced reflection radiance (`.rgb`) + confidence (`.a`) | `Rgba16Float` | every scene phase (cleared at the top of the scene render) | — | | `@scene.colorHistory` | the lit colour the target's previous render ended with | `Rgba16Float` | every phase | — | | `@scene.lights` | the punctual-light storage buffer: 64 light entries of twelve vec4s each (the light, then its punctual shadow record), followed by the virtual shadow map's region. A loop runs over the first `@frame.camera[4].w` entries, the lights in use; the buffer's length counts the shadow region too, so `arrayLength` does not size a light loop | storage buffer | every phase | — | | `@scene.environment` | the reflection-probe cube array | texture cube array | scene phases only | — | | `@scene.environmentSampler` | the filtering sampler for `@scene.environment` | sampler | scene phases only | — | | `@scene.reflectionProbes` | the environment buffer: the probe blend data naming which probe reaches a point, then the irradiance light-probe volumes | storage buffer | scene phases only | — | The rendering and ray-tracing guides (`guides { path = "topics/rendering" }`, `guides { path = "topics/raytracing" }`) point here rather than repeating this table. **Two g-buffer channels describe the surface, and they answer different questions.** `@scene.shaded` is what a surface SENT — the colour the geometry pass shaded it to, linear and scene-referred, so a surface lit above the display's peak reads above 1 there. `@scene.material` is what the surface IS: the base colour it reflects, its metallic and its perceptual roughness, each in [0, 1] and each independent of how brightly the surface happens to be lit. A pass that multiplies incoming light by a reflectance — a bounce multiplier, a Fresnel tint, an ambient floor — reads `@scene.material`; a pass that filters the picture reads `@scene.shaded`. `@scene.material` is an `Rgba8Uint` channel packing all three into 32 bits, so its slot declares `sample: uint` and the module unpacks it: ```yaml # bindings.yaml - { name: scene_material, kind: texture2d, sample: uint } ``` ```wgsl #include "@builtin::shaderModules.gbuffer_material" let m = zero_gbuffer_material(scene_material, coord); let bounce = incoming * m.base_color; ``` `@scene.albedo` is another name for `@scene.shaded` (the SHADED lit colour) and `@scene.mr` for `@scene.material` (the material channel). The engine logs the substitution once per name, naming the canonical one to write. `@scene.motion` carries screen-space velocity: the NDC displacement each pixel's surface underwent since the previous frame, so a still surface under a still camera reads `(0, 0)`. Opaque geometry contributes it on both render paths: the visibility raster writes it for every surface it records, and an opaque surface whose depth state the raster cannot express writes its own where it draws. A moving entity, a moving camera and an animated pose all reach it in the viewport; transparents, particles and sky carry none. A surface a material's `vertex()` hook displaces carries the displacement's own velocity. A render target's own camera and a capture keep no view history, so velocity there is the entity's motion with no camera term. `@frame.camera` is a reserved **buffer** input carrying the camera CURRENTLY being drawn: 10×`vec4<f32>` = the inverse view-projection (columns `[0..4)`, column-major) + camera world position (`[4].xyz`) + the previous render's view-projection (columns `[5..9)`), which projects a point into the picture that render left. A compute pass declares a `buffer` binding and binds it via `inputs = { name = "@frame.camera" }`, then reconstructs a pixel's world position from `@scene.depth`: ```wgsl let inv_vp = mat4x4<f32>(cam[0], cam[1], cam[2], cam[3]); // ndc.z is the `@scene.depth` sample itself. Scene depth is reversed — 1.0 is // the near plane, 0.0 the far plane and empty sky — and this matrix inverts // that same range, so a sample goes in unmodified. let wh = inv_vp * vec4<f32>(ndc, 1.0); let world_pos = wh.xyz / wh.w; ``` Like `@scene.*`, the engine resolves it **per render target** — so the same pass reconstructs against the live viewport's camera on screen and against an offscreen capture's / RTT camera off screen. (Pack a camera matrix into your own buffer instead and the offscreen render reconstructs against the wrong camera.) > Render-feature passes run in the main viewport render **and** in offscreen > captures / render-to-texture, each against its own camera. The `capture` tool's > `source = "position"` / `"entity"` therefore run the pass queue too; using > `@frame.camera` is what keeps those captures matching the live viewport. ### The environment A compute pass reads the scene's captured surroundings — the reflection-probe cube array, its sampler and the environment buffer (the probe blend data, then the irradiance light-probe volumes) — through three reserved inputs, bound to bindings of the shapes group(0) binds them in: ```yaml bindings: - { name: environment_map, kind: textureCubeArray } - { name: environment_sampler, kind: sampler } - { name: zero_environment, kind: buffer, access: read, element: ZeroEnvironment, array: false } ``` ```luau inputs = { environment_map = "@scene.environment", environment_sampler = "@scene.environmentSampler", zero_environment = "@scene.reflectionProbes", } ``` Named like that, `#include "zero::environment"` in the shader resolves the environment at a world point along a direction — `zpbr_sample_environment(world_pos, dir, lod)`, the probes whose radius reaches the point blended by rank and proximity, each through its proxy volume, and the sky under them — exactly as a material's environment term does, so a reflection a pass draws and one a material draws agree about the room they are in. The three bind at the scene phases; a post or UI phase carries none. A `textureCubeArray` binding takes `@scene.environment` alone, and a fragment pass has no slot of that shape. ## Pass kinds `enqueue` runs one of five kinds (the `kind` field; default `"fragment"`): - **`"fragment"`** — a full-screen shader over input textures. The program is a GPU **material** (or `shader`) the feature constructed; `inputs` bind live textures (`@scene.*` or RT guids), `output` is the target RT (omit = the phase's default scene target). Post-process, blur, edge effects. **Writing named G-buffer channels (`outputs`).** Instead of the single `output` RT, a fragment pass may declare an `outputs` array — one or more targets, each a named engine channel (`@scene.shaded` / `@scene.normal` / `@scene.emissive` / `@scene.color`) or an RT guid — each with its own blend mode: ```luau ctx.enqueue { kind = "fragment", shader = myShaderKey, outputs = { { target = "@scene.shaded", blend = "under" }, -- premultiplied dst-over-src { target = "@scene.emissive", blend = "additive" }, -- one fullscreen pass, two targets (MRT) }, phase = "afterOpaque", -- deferred: G-buffer filled, before the lighting composite } ``` Blend modes: `"replace"` (overwrite), `"alpha"` (source-over), `"additive"` (sum), `"under"` (premultiplied dst-over-src — accumulates coverage-weighted contributions). A `@scene.*` channel resolves only where it exists (the deferred G-buffer at a pre-composite phase); a pass whose targets are all unavailable at its phase is skipped (logged). `output` + `blend = true` remains the shorthand for a single alpha-blended target. The shader's returned colour is written to every target in the set. A fragment shader returns `vec4<f32>`, so the channels it can target are the float ones. `@scene.material` (also named `@scene.mr`) is `Rgba8Uint`, which binds as `uint` — naming it as an output is refused by name, with the channel's format and class in the log, and the rest of the frame draws. A fragment pass's `inputs` reads through the same fixed float slot, so naming `@scene.material` there is refused the same way; a compute pass reads that channel through a `sample: uint` slot instead. **What a pass with no `inputs` samples.** A fragment pass that declares no `inputs` reads `@scene.color` — the shape of an effect that filters the scene image. A pass that names `@scene.color` among its own `outputs` samples a 1x1 transparent texel instead, because the scene colour is that pass's render target and one texture is a colour attachment or a sampled resource in a render pass, never both. Declare `inputs = { src = "@scene.color" }` and write an RT to read the scene image and write somewhere else in one pass. - **`"compute"`** — a workgroup dispatch (`shader`, `storage`, `buffers`, `dispatch`; see "Compute passes"). - **`"geometry"`** — draw scene geometry with a constructed pipeline. The program is a **material** the feature built (`renderer.material.create`); the engine draws the scene's render-objects with that material's pipeline + uniforms. - **`"draw"`** — rasterize the feature's OWN geometry: `geometry` names a buffer created with `usage = { "vertex" }`, `storage.index` one created with `usage = { "index" }`, and `select` the one entity whose transform and material the draw lands through. `params[0]` is how many indices to submit — or name a buffer under `storage.indirect` (created with `usage = { "indirect" }`, holding a `DrawIndexedIndirectArgs` block: index count, instance count, first index, base vertex, first instance) and the count comes from the GPU instead, so a compute pass that compacts geometry pays only for what it kept and nothing waits on a read-back. `first_instance` must be 0; the engine resolves the entity's per-instance data another way, because a non-zero one needs a device feature WebGPU does not guarantee. - **`"splat"`** — rasterize a compute buffer of particle records as instanced camera-facing billboards into feature RTs (see "Splat passes"). ### Geometry passes A geometry pass re-draws the scene's meshes with a material you supply — the generic primitive for mesh-space effects (the engine names none of them): ```luau ctx.enqueue { kind = "geometry", material = myMaterial, -- the HANDLE renderer.material.create -- returned (or its registry-key string) geometry = "@geometry.opaque", -- which drawables: "@geometry.opaque" | -- "@geometry.transparent" | "@geometry.all" select = { entityA, entityC }, -- OPTIONAL: restrict to these entities -- (entity refs); omit = every matching mesh phase = "afterLighting", -- afterLighting = lit scene + valid depth } ``` `select` restricts the draw to the given entities — the per-instance signal that turns a whole-scene pass into a chosen-meshes effect. The **material** decides how those meshes are drawn; you control three things: - **Pipeline render-state.** `renderer.material.create` takes a `render` block — `cull` (`back`/`front`/`none`), `depthWrite` (bool), `blend` (`opaque`/`alpha`/`additive`) — so the pass can rasterize differently from the surface pass: ```luau local myMaterial = renderer.material.create({ shader = myShaderKey, -- a .shader you authored (identity, not guid) render = { cull = "none", depthWrite = false }, properties = { outline_color = { 1, 0.4, 0, 1 } }, -- seed the shader's uniforms }, "my_pass_mat") -- pass `myMaterial` (or "my_pass_mat") as the pass `material` ``` - **The shader.** A geometry `.shader` is a surface shader: author `fn vertex(v: VertexData) -> VertexData` to move vertices (object-local `v.position` / `v.normal`) and `fn fragment(input: FragmentData) -> vec4<f32>` for the colour. - **Its properties.** A shader reads ONLY the uniforms IT declares in `properties.yaml`, via `material.<yourProp>`. Referencing a field it didn't declare (e.g. a StandardMaterial `material.base_color`) fails to compile and the mesh renders **magenta** — declare the property or use a constant. What effect those three produce (outline, x-ray, wireframe, highlight, …) is yours to design — the engine just draws the selected geometry with your pipeline. ### Compute passes A compute pass dispatches a `.computeShader` program over a workgroup grid: ```luau ctx.enqueue { kind = "compute", program = myComputeShader, storage = { outTex = myStorageRtGuid }, -- slot -> storage-texture RT guid buffers = { particles = "my_particle_buf" },-- slot -> named compute buffer inputs = { camera = "@frame.camera" }, -- slot -> @frame.*/@scene.* buffer dispatch = { x = 64, y = 1, z = 1 }, } ``` **`dispatch` is optional.** Omit it and the pass is dispatched over what it WRITES: a grid covering its first `storage` texture, at the `@workgroup_size` the shader's entry point declares. With a screen-sized storage target that grid tracks the render target being drawn, so a screen-space effect covers the live viewport, an offscreen capture and an RTT camera without the feature knowing any of their resolutions: ```luau ctx.enqueue { kind = "compute", program = myComputeShader, inputs = { scene_color = "@scene.color", cam = "@frame.camera" }, storage = { outTex = myScreenSizedRt.guid }, -- screen = true phase = "afterLighting", } ``` State an explicit `dispatch` for a grid that is not one thread per output texel (a reduction, a particle sim), or when the shader's `@workgroup_size` is an override/const expression the engine cannot read. Each WGSL storage-buffer binding in the shader resolves its bound slot in this order: an explicit `buffers` mapping (the handle a buffer's owner holds, or a name), then `inputs` (`@frame.camera` / `@scene.lights` / `@scene.reflectionProbes`), then — when a slot has neither — a buffer whose engine-side name equals the slot's own name. `buffers` is the seam a pass binds through: the buffers a shader works over are the ones handed to it, whatever each is called. `storage` binds storage TEXTURES (RT guids) the same way, one map per resource kind. ### Splat passes A splat pass draws every record of an f32 buffer as a camera-facing billboard — the raster primitive behind screen-space particle surfaces (the `fluidSurface` system is built entirely on it): ```luau ctx.enqueue { kind = "splat", phase = "afterLighting", output = depthRt.guid, -- or `outputs` for the thickness+color MRT splat = { buffer = "my_particles", -- compute-buffer name stride = 12, -- floats per record posOffset = 0, -- float offset of the position count = 200000, -- records to draw radius = 0.3, -- world particle radius channel = "depth", -- "depth" | "thickness" | "sprite" | "gaussian" velOffset = 4, -- optional: velocity → screen-space stretch stretch = 0.04, -- seconds of motion elongating the billboard colorOffset = 8, -- optional (thickness): + per-particle RGB → MRT weightOffset = 7, -- optional (sprite): per-particle intensity minY = -60.0, -- records below this y collapse (parked/dead) maxRadiusPx = 120, -- optional: cap on the projected pixel radius }, } ``` The `"gaussian"` channel draws the engine's packed splat records — what `renderer.splat.components` decodes a `.spz` or `.ply` capture into — as elliptical-weighted-average Gaussians, and takes fields of its own: ```luau splat = { buffer = "cloud_records", stride = 6, -- the packed record is six u32 words posOffset = 0, count = 1200000, radius = 1.0, -- multiplies each splat's stored scale channel = "gaussian", orderBuffer = "cloud_order", -- back-to-front permutation; "over" needs one shBuffer = "cloud_sh", -- optional: quantized higher-order SH shStride = 24, -- u32 words of SH per record shDegree = 3, transform = model, -- object -> world, column-major, 16 floats prevTransform = prevModel, -- where `transform` stood last frame opacityScale = 1.0, } ``` `transform` places the cloud: each Gaussian's covariance is conjugated by its upper-left 3×3, so a non-uniform scale shears the cloud the way it shears a mesh. `prevTransform` plus a second entry in `outputs` makes the channel write an MRT pair — the colour into the first target, and the screen-space displacement each splat underwent between the two placements into the second, premultiplied by the same alpha the colour composites under. That second target therefore resolves to `(coverage-weighted mean displacement, coverage)`, which is what folds a moving cloud into `@scene.motion`. Naming one target, or leaving `prevTransform` out, renders the colour alone. The other three channels write different fragments: `"depth"` writes nearest-surface linear view depth (R32Float, hardware-depth-tested on the target's own depth buffer), `"thickness"` accumulates additive optical thickness (with `colorOffset` and a two-entry `outputs` list it also accumulates thickness-weighted color into the second target), and `"sprite"` accumulates a soft additive disc scaled by `weightOffset`. Every channel discards fragments behind opaque scene geometry by sampling the scene depth at the fragment's own NDC. `maxRadiusPx` scales down billboards whose projected major radius would exceed that many pixels, so particles crossing the near plane stay droplet-sized instead of filling the screen. Targets clear at the pass; `blend = true` on the spec loads them instead to accumulate over a prior splat pass. `renderer.feature.create(featureRef)` instantiates a feature and returns a live handle (`featureRef` may be an `AssetRef<renderFeature>` or its identity string). The handle appears under `/zero/runtime/generated_features/<guid>/`. Re-creating the SAME feature asset replaces the live one (hot-reload after editing `init.luau`) rather than stacking a duplicate. - `renderer.feature.list()` → `{ {guid, identity} }` for every live feature. - `renderer.feature.destroy(handleOrGuid)` (or `renderer.destroy(handle)`) tears one down — by handle OR by guid string, so you can stop a feature even after losing its handle (e.g. across separate `execute` calls). ## In the Inspector Selecting a render feature opens its **Feature** section: whether the feature runs in this session, an Enable or Disable action, and its settings as typed controls. While it runs, the controls hold its live values and an edit reconfigures the running feature (`renderer.feature.configure` checks it against the schema first). Those edits are session state: they change the running feature only, they are not undoable (Ctrl+Z never reaches them), and Disable or a restart ends them; the feature's declared defaults are what the next Enable starts from. While it does not run, the controls show the declared defaults, read-only, and a write reaching it then is refused. A feature enabled, disabled or reconfigured from a script shows in the section as it happens. A feature that declares no settings says so.

# Shader module (asset type) A `.shaderModule` is a block of WGSL that other shaders **include** rather than copy — a lighting model, a set of colour-space helpers, one package's shared prelude. It declares no entry point and is never dispatched or drawn on its own account; it exists to be expanded into the shaders that name it. ## Folder shape ``` <name>.shaderModule/ module.wgsl # the WGSL — helpers, structs, constants (required) README.md # what THIS module provides (required) .metadata # tags and free-form fields (required) ``` Each file carries a committed `.meta` sidecar pinning its stable guid, and the folder carries one of its own. ## Including one A shader names a module by identity, and the identity is what records the dependency — so a shader that is packed, pulled or published carries the modules it includes with it: ```wgsl #include "~.colour" // a module under the same `~.` #include "@builtin::shaderModules.pbr_shading" // one from the builtin library ``` A missing module is a hard error at compile: a shader that names an interface which no longer exists fails loudly rather than compiling against a stale copy. Each module is expanded at most once per shader, so two shaders that both include the same module — or a module that includes another — produce one copy, not a duplicate-definition error. ## Writing one Write only what other shaders need in scope: functions, structs, constants. A module may reference a binding its includers declare, which is how a package's prelude can read that package's uniform block. ```wgsl const LUMA: vec3<f32> = vec3<f32>(0.2126, 0.7152, 0.0722); fn srgb_to_linear(c: vec3<f32>) -> vec3<f32> { let lo = c / 12.92; let hi = pow(max(c + vec3<f32>(0.055), vec3<f32>(0.0)) / 1.055, vec3<f32>(2.4)); return select(hi, lo, c <= vec3<f32>(0.04045)); } ``` ## Answering to another name A module declares extra names it answers to with `@alias` lines in the header of `module.wgsl`: ```wgsl // @alias: colour_helpers // @alias: @mypack::shaderModules.colour ``` Each becomes an alias on the asset, so the name resolves everywhere an identity does: `asset.resolve`, an `#include`, and the publish gate alike. Only the header is read — the scan stops at the first line that is not a comment, so a directive cannot hide in the module body. A name another asset already holds is refused and reported, since an alias extends the identity namespace rather than taking a name out of another asset's hands. ## Registration & hot reload Writing `module.wgsl` registers the module under every name the asset answers to — its guid, its identity, and any alias — so a shader includes it by whichever name it holds. Saving re-registers it and the shaders that include it recompile, with no world reload. ## Discovery - `asset.list("shaderModule")` — every registered module. - `moduleRef:getSource()` — the module's WGSL. ## Related types - `.shader` — render-domain shaders (surface, sky, post-process, screen). - `.computeShader` — compute programs. ## In the Inspector Selecting a shader module opens its **Module** section: how many lines it holds, the aliases a shader `#include`s it by, and an opener for `module.wgsl`.

# Compute shader (asset type) A `.computeShader` is a GPU compute (GPGPU) program with a **zero-scaffolding** authoring contract: you write only `@compute fn main(...)` plus a declarative `bindings.yaml`, and the engine GENERATES every `@group/@binding` declaration — storage buffers, textures, samplers, storage textures, and a `params:` uniform — expands `#include`s, naga-validates the result, and registers it. The single source of truth for the binding layout is `bindings.yaml`; there are no hand-written `@binding` lines to keep in sync. > New to how content lives across the CPU and GPU? Read `core/resource-model` > first: it covers the asset / CPU / GPU forms every resource takes, the upload > path, and how compute fits the performance ladder (`core/performance`). ## Folder shape A `.computeShader` is a folder asset: ``` <name>.computeShader/ shader.wgsl # the WGSL body — only `@compute fn main` + helpers (required) bindings.yaml # the binding + params schema (required) README.md # a one-paragraph description of THIS shader (required) .metadata # asset metadata ``` Each file carries a committed `.meta` sidecar pinning its stable guid. The identity is `<name>` (the `.computeShader` suffix strips). Resolve the shader once, then dispatch through the reference: ```lua local carve = asset.resolve("carve", "computeShader") carve:dispatch({ buffers = { heights }, workgroups = { 64 } }) ``` `asset.resolve` is what records your script's dependency on the shader, so the shader travels with the world your script lives in — packed, pulled, or published. It compiles on first dispatch; there is no setup step. ## bindings.yaml One ordered `bindings:` list — the binding index is the list position (0, 1, 2, …) — plus an optional `params:` scalar-uniform block. `kind` defaults to `buffer` when omitted. ```yaml bindings: - { name: clouds, kind: storage3d, format: rgba16f } # texture_storage_3d<rgba16float, write> - { name: occupancy, kind: texture3d } # texture_3d<f32> - { name: smp, kind: sampler } # sampler - { name: out_tex, kind: storage2d, format: rgba16f } # texture_storage_2d<rgba16float, write> - { name: U, kind: buffer, access: read, element: f32 } # var<storage, read> U: array<f32> - { name: Uniforms, kind: buffer, access: read, element: VolumeUniforms, array: false } # var<storage, read> Uniforms: VolumeUniforms params: - { name: scale, type: float, default: 2.0 } - { name: count, type: int, default: 0 } ``` | `kind` | extra keys | generated WGSL declaration | |---|---|---| | `buffer` (default) | `access: read \| read_write` (default `read_write`), `element: <wgsl type>` (default `f32`), `array: true \| false` (default `true`) | `var<storage, ACCESS> NAME: array<ELEMENT>;` (or `… NAME: ELEMENT;` when `array: false`) | | `texture3d` | — | `var NAME: texture_3d<f32>;` | | `texture2d` | `sample: float \| uint \| sint` (default `float`) | `var NAME: texture_2d<f32>;`, or `<u32>` / `<i32>` for the other classes | | `texture_depth` | — | `var NAME: texture_depth_2d;` — the one sampled shape with no `sample:` of its own; a depth-aspect channel (`@scene.depth`) binds here, not through `texture2d` | | `storage3d` | `format`, `access: write \| read \| read_write` (default `write`) | `var NAME: texture_storage_3d<FMT, ACCESS>;` | | `storage2d` | `format`, `access: write \| read \| read_write` (default `write`) | `var NAME: texture_storage_2d<FMT, ACCESS>;` | | `sampler` | — | `var NAME: sampler;` | | `textureCubeArray` | — | `var NAME: texture_cube_array<f32>;` — the environment cube array, bound to `@scene.environment` by a render feature's pass | | `vertices` | `access: read \| read_write` (default `read_write`) | `var<storage, ACCESS> NAME: array<u32>;` plus the mesh's layout uniform and the `zeroVertex*` accessors | | `acceleration_structure` | — | `var NAME: acceleration_structure;` (hardware ray tracing) | - **Eight storage buffers per shader** — the WebGPU guarantee, and what the engine asks every device for. `buffer` and `vertices` bindings spend that budget; textures, samplers, storage textures and `params:` do not. An `acceleration_structure` brings engine-owned buffers with it — **three** where the device has hardware ray query (the tables `zeroHitSurface` / `zeroMaterial` read) and **five** on the software backend (those, plus the scene triangles and the hierarchy over them) — so a traced pass has three slots of its own on the backend web users get. Over budget, the engine refuses the shader and logs which buffers it declared. - A `buffer` defaults to `array<ELEMENT>`. Set `array: false` for a single NON-array storage buffer — a struct binding (e.g. `element: VolumeUniforms`, `array: false` → `var<storage, read> NAME: VolumeUniforms;`). The struct definition itself lives in `shader.wgsl`, not `bindings.yaml`. - **A sampled texture binds under the class its FORMAT puts it in**, so `sample` states that class and the generated `texture_2d<..>` matches it. An integer channel — `@scene.material`, which is `Rgba8Uint` — is `uint`; everything else is the `float` default. Bind an integer channel to a `float` slot and the engine refuses the pass and names both classes, because the device would otherwise reject the bind group and invalidate the pipeline. - A storage texture's `access` decides both the generated declaration and the layout the engine registers, so the two always agree. It defaults to `write`, the access every target grants every storage-compatible format. `read_write` is granted on `r32f` alone; declaring it on any other format is refused at the compile, with the reason on `compute.programState`. A pass that needs to read a wider target reads it through a separate `texture3d` / `texture2d` binding, or through a second storage binding declared `read`. - `format` tags (storage textures): `r8`, `r16f`, `r32f`, `rgba8`, `rgba16f`, `rgba32f`. Storage textures only allow storage-compatible formats (`r32f` / `rgba8` / `rgba16f` / `rgba32f`). - An `acceleration_structure` binding resolves to the scene acceleration structure when the shader runs as a render-pass with ray tracing enabled (`renderer.setRaytrace(true)`). Declaring one makes the engine emit the helper functions the body can call: `zeroTraceClosest(origin, dir, t_min, t_max) -> ZeroHit` (struct: `hit, t, instance, primitive, bary, attr`, where `instance` is the hit object's render slot), `zeroTraceAny(origin, dir, t_min, t_max) -> bool` (terminate-on-first-hit, for shadow/occlusion rays), and `zeroHitSurface(hit) -> ZeroSurface` (`normal, uv, material`) + `zeroMaterial(index) -> ZeroMaterial` (`base_color, emissive, metallic, roughness`) to shade what a hit landed on. The same surface works on both backends — hardware ray query and the software/compute path — so the shader doesn't branch on `renderer.raytraceCapability()`. Bind it from a render-pass, which is where the scene acceleration structure exists. `params:` declares scalar uniforms (`type: float | int`). When non-empty the engine appends a `ZeroComputeParams` uniform as the trailing binding (read it in WGSL as `params.<name>`) and tunes its values at runtime with `shaderRef:setParam(prop, value)`. ## The kernel ABI: `columns`, counted and appended outputs, `specialize`, `determinism` One shader asset can serve many shapes of data. `bindings.yaml` states the shape with these extensions, and the engine's compile path lowers them to the plain bindings and WGSL above (`modules/compute_abi`, whose README has the whole surface): ```yaml workgroup: 64 # the size the body declares (default 64) bindings: - { name: cols, kind: columns, access: read } # a table of columns in one binding - { name: src, kind: buffer, access: read, element: T } - { name: dst, kind: buffer, access: read_write, element: T, count: "len(src)" } - { name: hits, kind: buffer, access: read_write, element: vec4<f32>, capacity: "n * 4", append: true } specialize: - { name: T, options: [f32, i32, vec2<f32>, vec3<f32>, vec4<f32>] } - { name: FOLD, options: [add, min, max] } - { name: BODY, kind: source, default: "0.0" } # text that replaces the identifier determinism: exact # or float_order ``` - A `buffer` of a scalar or vector element gets `NAME_get(i)`, `NAME_len()` and (unless `access: read`) `NAME_set(i, v)`. A `vec3` element is stored as a flat scalar array, so a column of vec3 keeps its 12-byte stride. `zero_n()` is the dispatch size. - `columns` binds a table of columns (`compute_abi.table`) as one storage buffer; `cols_f32(c, i, lane)`, `cols_vec3(c, i)` and the rest read it. - `count` / `capacity` give the size, in elements, of an output the run allocates. `append: true` adds a live counter binding, `NAME_count`, with `NAME_store(slot, v)`, `NAME_set_count(n)` and, under `determinism: float_order`, `NAME_append(v)`. - `specialize` parameters are compile-time: type options become `alias NAME`, named options become `const NAME` and `NAME_<option>`, `kind: source` text replaces the identifier. Each specialization compiles once. - `determinism: exact` refuses `NAME_append`: an exact output is written at ranks the kernel computed. Dispatch such a shader through its program: ```lua local variant = shaderRef:program():variant({ specialize = { T = "vec3<f32>" } }) local run = variant:run({ n = 64, inputs = { src = srcBuffer } }) local values = require("@builtin::modules.compute_abi").read(run.outputs.dst.buffer) ``` `shaderRef:program()` answers the same program, with the variants it has lowered and compiled, for as long as `shader.wgsl` and `bindings.yaml` hold the bytes they held when it was made. A write to either file, from any origin (`vfs.contentVersion` moves), makes the next `program()` a new one, and a dispatch through it runs the new text. The schema `getBindings()` answers is the one the program was made over. ## Writing a mesh's vertices — `kind: vertices` A mesh's vertices are raw bytes on the GPU, and the engine stores a mesh in one of two layouts: 92 bytes a vertex with every attribute a `f32`, or 32 bytes a vertex with normals and tangents quantized to bytes and UVs to shorts. Which one a mesh got depends on the mesh. Declare `kind: vertices` and the shader is handed both the buffer and the layout that mesh is in, plus accessors that address it: ```yaml bindings: - { name: verts, kind: vertices } # the mesh, writable - { name: heights, kind: buffer, access: read, element: f32 } params: - { name: lift, type: float, default: 1.0 } ``` ```wgsl @compute @workgroup_size(64) fn main(@builtin(global_invocation_id) id: vec3<u32>) { if (id.x >= zeroVertexCount()) { return; } var p = zeroVertexPosition(id.x); p.y = p.y + heights[id.x] * params.lift; zeroSetVertexPosition(id.x, p); zeroSetVertexNormal(id.x, vec3<f32>(0.0, 1.0, 0.0)); } ``` ```lua carve:dispatchOnVertices({ model = meshRef:handle().guid, buffers = { heights }, workgroups = { 64 } }) ``` The accessors, over a binding declared `read_write`: | read | write | |---|---| | `zeroVertexCount() -> u32` | — | | `zeroVertexPosition(i) -> vec3<f32>` | `zeroSetVertexPosition(i, vec3<f32>)` | | `zeroVertexNormal(i) -> vec3<f32>` | `zeroSetVertexNormal(i, vec3<f32>)` | | `zeroVertexTangent(i) -> vec4<f32>` | `zeroSetVertexTangent(i, vec4<f32>)` | | `zeroVertexUv(i) -> vec2<f32>` | `zeroSetVertexUv(i, vec2<f32>)` | | `zeroVertexColor(i) -> vec4<f32>` | `zeroSetVertexColor(i, vec4<f32>)` | | `zeroVertexNodeIndex(i) -> u32` | — | | `zeroVertexWord(i, offset) -> u32` | — | `access: read` gives you the readers only — a `var<storage, read>` binding cannot be assigned to, so the writers are left out rather than handed to you broken. Once a pass has written a mesh's vertices, the engine bounds that mesh by what the pass wrote: it reduces the vertices to an AABB every frame and culls against that, so geometry a pass moves across the scene needs no oversized placeholder to survive culling. `renderer.mesh.boundsSource(guid)` reports `"compute"` for such a mesh and `"geometry"` for one still bounded by what it was created with. A shader declares at most one `vertices` binding; the accessors are generated for that mesh. It can be declared anywhere in the list — the mesh is bound by the dispatch, and `buffers` fills the other storage slots in declaration order. The tangent's `w` carries handedness, and quantized normals/tangents come back in -1..1 while quantized UVs and colours come back in 0..1, so the values are the same ones a surface shader sees whichever layout the mesh is in. ## shader.wgsl Write only `@compute fn main` (and any helpers / `#include`s). The names declared in `bindings.yaml` are in scope — `data`, `out_tex`, `params.scale`, … — with no `@group`/`@binding` lines of your own. ```wgsl // @domain: compute // Bindings are declared in bindings.yaml — do NOT write @group/@binding here. @compute @workgroup_size(64) fn main(@builtin(global_invocation_id) id: vec3<u32>) { if (id.x < arrayLength(&data)) { data[id.x] = data[id.x] * 2.0; } } ``` ## Dispatch & runtime Everything a compute shader does, it does through its reference: | method | what it does | |---|---| | `ref:dispatch(opts)` | `{ buffers, workgroups, params? }` — bind one buffer per declared storage binding, in order | | `ref:dispatchOnVertices(opts)` | `{ model, buffers?, workgroups, params? }` — bind the mesh `model` names to the `vertices` binding, `buffers` filling the rest | | `ref:dispatchEx(opts)` | `{ resources, workgroups }` — for shaders mixing textures, samplers and storage textures: one `{ kind, name }` per declared binding, in order | | `ref:setParam(prop, value)` | write one `params:` scalar uniform | | `ref:createBuffer(name, opts)` | `{ type, len, usage? }` — a GPU buffer owned by this shader | | `ref:buffer(name)` | the buffer this shader last made under `name` | | `ref:getBindings()` | the parsed `bindings.yaml` schema, read and parsed again only after the file is written | | `ref:getSource()` / `ref:setSource(wgsl)` | read / overwrite `shader.wgsl` | | `ref:compile()` | compile now instead of on the first dispatch | | `ref:status()` | what the engine did with this shader's dispatches, one record per target | The `params:` uniform is engine-owned and takes no entry in `buffers` or `resources`, and neither does a `vertices` binding's layout. `setParam` writes the uniform every later dispatch reads. A dispatch that passes `params = { name = value }` reads those values instead, in a copy of the uniform only it binds, with every name it leaves out at the value the shader holds — so one shader dispatched twice in a frame over different data reads different values each time: ```lua lift:dispatch({ buffers = { a }, workgroups = { 4 }, params = { height = 1.0 } }) lift:dispatch({ buffers = { b }, workgroups = { 4 }, params = { height = 3.0 } }) ``` A name the shader does not declare fails that dispatch, and the failure names what it does declare. ### `dispatchEx` resources Each `resources` entry fills the binding at its position. Its `kind` says what the resource is, in the words `bindings.yaml` uses, and the binding decides how it is read. A slot takes the kind it is declared with; a `texture2d` slot also reads a storage texture, a side of a history pair or the scene depth, and a `storage2d` slot also writes this frame's side of a history pair: | binding's `bindings.yaml` kind | `resources` entry | `name` | |---|---|---| | `buffer` | `{ kind = "buffer", name = buf }` | a buffer handle from `ref:createBuffer` | | `texture3d` | `{ kind = "texture3d", name = vol }` | a 3D texture handle from `ref:createTexture3D` | | `storage3d` | `{ kind = "storage3d", name = vol }` | a 3D texture handle from `ref:createTexture3D` made with `storage = true` | | `storage2d` | `{ kind = "storage2d", name = target }` | a storage texture handle from `ref:createStorageTexture2D` | | `storage2d` | `{ kind = "history_curr", name = history }` | a history pair from `ref:createTextureHistory`: this frame's side | | `texture2d` | `{ kind = "texture2d", name = tex }` | a handle `ref:copyBufferToTexture` returns, or a texture asset's guid once `texRef:handle()` has made it GPU-resident | | `texture2d` | `{ kind = "storage2d", name = target }` | a storage texture handle, read as a texture | | `texture2d` | `{ kind = "history_prev", name = history }` / `{ kind = "history_curr", name = history }` | a history pair: the previous frame's side or this frame's | | `texture2d` | `{ kind = "scene_depth" }` | none: the frame's scene depth | | `sampler` | `{ kind = "sampler", name = smp }` | a sampler handle from `ref:createSampler` | `texture3d` and `storage3d` name the same resource, a 3D texture, so either one fills either slot. The engine's own spellings name the same resources and keep working: `texture_3d` for `texture3d` and `storage3d`, `texture_2d` for `texture2d`, and `storage_2d` for `storage2d`. Any other `kind` is refused at the call, naming every kind it accepts. A `vertices` binding is filled by `ref:dispatchOnVertices`, and `texture_depth`, `textureCubeArray` and `acceleration_structure` bindings by a render feature's pass. ```lua local march = asset.resolve("volume_march", "computeShader") -- bindings.yaml: density (storage3d), out_tex (storage2d), U (buffer) march:dispatchEx({ resources = { { kind = "storage3d", name = density }, { kind = "storage2d", name = target }, { kind = "buffer", name = uniforms }, }, workgroups = { 8, 8, 8 }, }) ``` `workgroups` is `{ x, y, z }`, `{ x }`, or a bare `x`, and every dimension it leaves out is 1. A zero in any dimension is refused: the dispatch is dropped and recorded as a failure, so it surfaces in `ref:status()` and `compute.failing()` with the reason. A count derived from how much data there is passes through `math.max` first, so an empty set dispatches one workgroup rather than none: ```lua carve:dispatch({ buffers = { heights }, workgroups = { math.max(1, math.ceil(#points / 64)) } }) ``` ### Buffers and readback (the CPU side) A buffer is created through the shader that owns it and comes back as a handle. Pass the handle to a dispatch — including another shader's — to bind it there: ```lua local double = asset.resolve("@builtin::shaders.compute_double", "computeShader") -- `type` is the element the shader declares, `len` how many of them. local data = double:createBuffer("data", { type = "f32", len = 4, usage = { "readback" } }) data:write({ 1.0, 2.0, 3.0, 4.0 }) -- :writeU32 for integer words, :writeBytes for packed bytes double:dispatch({ buffers = { data }, workgroups = { 1, 1, 1 } }) local pending = data:read() -- starts an async GPU->CPU readback -- a frame or two later, drain it (nil until it has arrived): local out = pending:result() -- :resultU32 / :resultBytes read the same bytes another way data:destroy() -- free it when done ``` `type` is one of `"f32"`, `"vec3"`, `"vec4"`, `"quat"`, `"mat4"`, and `usage` adds `"readback"`, `"vertex"`, `"index"` or `"indirect"` on top of the storage a buffer always has. An `"indirect"` buffer holds a draw's arguments where the GPU reads them, so a shader that compacts geometry writes the drawn count into the same dispatch that produced it and a render feature's `kind = "draw"` pass submits exactly that — the `renderFeature` asset type's README documents that pass and the `storage.indirect` name it reads. The handle's key is the shader's guid plus the name you gave it and a serial, so two shaders that both want a buffer called `data` get one each — and so do two callers asking this same shader for one. `ref:buffer(name)` returns the last one made under that name, which is how two callers share one on purpose. A buffer that no shader computes — a vertex or index run that is only ever drawn — is allocated straight from the primitive instead: `substrate.createBuffer({ name = ..., type = ..., len = ..., kind = "gpu", usage = { "vertex" } })`. The first dispatch of a shader compiles it, so the very first readback can still reflect the un-run shader; dispatch again once it is compiled, or `ref:compile()` to pre-warm. This create/write/dispatch/readback loop is the CPU side of the resource model in `core/resource-model`. ### Is it compiled? `ref:compile()` queues the compile; the pipeline is built on the render side frames later, so that call cannot say whether it produced a program. `compute.programState(ref)` is where that lands: ```lua if compute.programState(carve) == "ready" then carve:dispatch(opts) end local state, reason = compute.programState(carve) if state == "failed" then print(reason) end ``` - `"absent"` — the engine holds nothing under this key and nothing is in flight: never asked for, or released. - `"pending"` — a compile was asked for and has not reached the device. A recompile of a resident program reads pending too, because what it produces is a different program from the one bound now — which is what makes this the precondition to wait on after an edit. - `"ready"` — compiled and resident, so a dispatch naming it binds it. - `"failed"` — the most recent compile produced no program, and the second return says why. A dispatch issued while the program is `"pending"` is held behind the compile and dropped if it never lands, so a readback taken before `"ready"` reports the buffer as it was. Wait for `"ready"`, not for a count of frames. ### Did it run? A dispatch is recorded into a command encoder frames after the call that asked for it returned, so that call's `true` means "queued", not "ran". `ref:status()` is where the outcome lands — one record per target, cumulative: ```lua for _, d in ipairs(carve:status()) do print(d.target, d.ok, d.dispatches, d.failures, d.lastError) end ``` `target` is the mesh guid for a `dispatchOnVertices` and the buffers it bound for a dispatch that writes only those, so two systems driving one shader over their own buffers read as the two passes they are. `ok` is the most recent outcome; `lastError` says why the last failure failed and is kept after a recovery. An empty result means nothing has dispatched this shader at all. `compute.failing()` answers the same question across every shader at once. A failing dispatch also posts a notice, so a pass that stops running reports itself rather than waiting to be found. ### Running one every frame A `kind = "compute"` substrate job queues one dispatch per frame: ```lua jobs.register({ phase = "main", executor = { kind = "compute", shader = asset.resolve("carve", "computeShader"), buffers = { "heights" }, workgroups = { 64 }, }, }) ``` ## Registration & hot reload Writing `shader.wgsl` or `bindings.yaml` fires the `.computeShader` assetType's `onChange`, which compiles it: the binding declarations are generated, `#include`s expanded, the WGSL validated, and the shader registered. This happens on create and on every edit, so saving recompiles with no world reload. A shader with invalid WGSL (a type mismatch, an undefined name) **fails to compile** with the reason logged (`[compute] Compile of '<name>' failed: …`) and is **not** registered. You don't need to register a shader before dispatching it — the first dispatch auto-compiles it on use. `ref:compile()` remains as an optional explicit pre-warm, only to avoid the one-frame first-dispatch warm-up in a latency-critical spot. ## What compute is holding, and why a key names nothing Every buffer, volume, storage target, history pair and sampler a dispatch can bind is filed under a key, and `compute.observe()` lists all of them with what each costs: ```lua local r = compute.observe() print(r.totals.count, r.totals.bytes) for _, res in ipairs(r.resources) do print(res.key, res.kind, res.bytes, res.owner.name) end ``` A row carries the key verbatim — the same string a dispatch names it by and a dispatch-failure message prints — plus its `kind`, its `bytes`, its extent and `format` where it has them, the `usage` bits it was created with, and the frame it was created on. `owner` is read back out of the key (`<shader-guid>::<name>#<serial>`), so a resource nothing has ever dispatched over still names the shader that made it. `compute.resources(ref)` narrows to one shader's — including the `<shader-guid>::__params` uniform the compile created for a `params:` block, which the shader owns like any other resource. `r.totals.bytes` is the `compute` figure of `renderer.gpuMemory()` — the two are read off the same registries, so a listing accounts for the category exactly. The same reading is served at `/zero/runtime/compute`. When a key names nothing, `compute.diagnose(key)` says which of the states the inventory distinguishes it is in, from the closed set `compute.absentReasons()` enumerates: | reason | what the inventory read | |---|---| | `resident` | a resource is filed under exactly this key; the row is on `resource` | | `replaced` | the owner holds the same name at a different serial — `current` names the live key | | `nameUnused` | the owner holds resources, none under this name | | `ownerAbsent` | no live resource carries this key's owner | | `unowned` | the key carries no owner segment, and nothing is filed under it | | `notPublished` | no renderer has published an inventory, so no key can be answered for | So a key out of `[compute] dispatch '…' failed` resolves against what exists, and a typo reports which part of it the engine could not match rather than coming back empty. A reason is the inventory at the moment the call read it. The reading is republished on a frame where a registry gained or lost an entry, so a resource created and diagnosed inside one script sees the reading from before it was made; wait a frame and ask again. ## Discovery - `asset.list("computeShader")` — every registered compute shader. - `asset.inspect("<name>")` — status, source, parse errors, this README. - `computeRef:getBindings()` — the parsed `bindings.yaml` schema (`{ bindings, params }`). - `compute.programState(ref)` — whether the program is compiled, still compiling, or failed, and why. - `compute.observe()` — every GPU resource compute holds, and what it costs. - `compute.diagnose(key)` — whether a key names a live resource, and why not. - `profiler.gpuFrame()` — what each dispatch of this shader spends on the GPU. A dispatch is timed under `compute.<identity>` — the same identity `asset.resolve` takes, so a timing row names the shader that produced it. ## Common pitfalls - **Compute shaders don't render** — verify output via a buffer readback or a debug pass, not a screenshot. - **`ref:compile()` returns before the program exists** — the pipeline is built on the render side; `compute.programState(ref)` says when it is `"ready"`. A dispatch issued before that is held behind the compile and dropped only if the compile never lands. - **A dispatch call returning true means queued** — ask `ref:status()` whether it ran. - **A destroyed buffer is refused where it is bound** — a handle outlives its storage, and `buf:alive()` reports which. - **Binding order is the contract** — `buffers` and `resources` bind in `bindings:` list order; reordering the list reorders the bindings. - **Don't write `@group`/`@binding` in `shader.wgsl`** — the engine owns them; re-declaring is the fastest way to a layout mismatch. - **Don't infer a mesh's vertex stride** — declare `kind: vertices` and use the accessors. A wrong stride writes positions correctly and normals into the wrong word, which renders as flat lighting rather than as broken geometry. - **Storage-texture format must be storage-compatible** — `r32f` / `rgba8` / `rgba16f` / `rgba32f`; others are rejected at compile. - **A key that comes back empty is not the same as one that failed** — `compute.diagnose(key)` separates a name never used from a generation that was replaced, and names the live key in the second case. ## Related types - `.shader`: render-domain shaders (surface, sky, post-process, screen). ## In the Inspector Selecting a compute shader opens its **Compute** section: whether its program is ready (and why not), how many dispatches it has run and failed in this session (and the last error), tables of the bindings and params its `bindings.yaml` declares, and openers for `shader.wgsl` and `bindings.yaml`.

# 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**.

# 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.

# systemSettings Which of several components stating one scene-wide system's settings is in force. A scene-wide system (screen-space reflections, ambient occlusion, depth of field, fog, exposure, environment lighting, weather, ...) runs under one set of settings, and more than one component instance can state them at once: two hosts in one scene, an instance and the one replacing it while a script reloads, or the instances a scene module's builder makes while it records a rebuild beside the ones its last build placed. Each component instance takes a claim on the system and states its settings through it every frame: ```lua local Ssr = require("@builtin::systems.reflections.ssr") local systemSettings = require("@builtin::modules.systemSettings") local claim = systemSettings.claim("@builtin::systems.reflections.ssr", { push = Ssr.set, -- puts the settings in force release = Ssr.clear, -- takes the system down live = Ssr.active, -- whether the system is up }) function update(_dt) claim:state(signatureOf(opts()), opts()) end function onDestroy() claim:release() end ``` ## What is in force The claims on one system are kept in the order they last stated something new, and the newest is in force. - A claim whose settings changed moves to the newest place and pushes them: the last component edited wins. - A claim that joins stating exactly what is in force takes the newest place and pushes nothing. - Releasing a claim while others are live hands the system to the newest of them, which pushes its own settings when they differ. Only the last claim released takes the system down. - The claim in force pushes again when the system it brought up is no longer up (a script's `clear()`, a feature torn down from outside), so a component standing in the scene keeps its system running. A push that left the system down, such as a setting that turns it off, is not repeated. ## Exports - `systemSettings.claim(key, spec) -> Claim`: a claim on the system named `key` (the path of the module that drives it). `spec.push(opts)` puts settings in force, `spec.release()` takes the system down, and the optional `spec.live()` says whether it is up. - `claim:state(sig, opts)`: state the settings for this frame. `sig` is a string that differs whenever `opts` does. - `claim:release()`: let the system go, from `onDestroy`. - `claim:inForce() -> boolean`: whether this claim's settings are in force. - `systemSettings.count(key) -> number`: how many live claims state the system.

# surface_flags The per-pixel surface-flag field, and the one encoding of it. A screen-space pass sees a pixel's colour, depth and normal — enough to ask where a surface is and which way it faces, and not enough to ask what kind of surface it is. This field answers that: the geometry pass writes a small set of per-pixel surface properties into the alpha of the G-buffer normal, and any pass that reads `@scene.normal` reads them back. `ZERO_SURFACE_FLAG_FOG_EXEMPT` is the one a material controls today. The `pbr` shader's `receives_fog` property drives it, and the screen-space fog passes — `heightFog` and `aerialPerspective` — leave an exempt pixel at the colour it shaded to however deep in the medium it stands. The field is 2 bits, carried in the alpha of an `Rgb10a2Unorm` target, because the pass that fills the G-buffer already holds the 128 bits of colour a pixel a tile-based GPU keeps on chip at its full tile size. A pixel no geometry wrote reads 0 — no flags — so every flag is opt-in and the sky behaves as an ordinary participating surface. Pure math, no bindings. ```wgsl #include "@builtin::shaderModules.surface_flags" let n = textureLoad(scene_normal, coord, 0); if !zero_surface_takes_fog(n.a) { textureStore(out, gid.xy, base); return; } ``` A shader that wants a surface exempt declares it from `surface()` or `fragment()`: ```wgsl zero_set_fog_exempt(true); // this pixel takes no fog ``` The field is a G-buffer channel, so the deferred G-buffer fragment entry is what writes it: an opaque draw on the deferred path. A draw that goes through the forward fragment entry — every draw on the forward path, and the transparent phase on either path — leaves the pixel carrying whatever the surface behind it wrote.

# lighting Scene-lighting base capability: ambient + directional ("sun") light and procedural-sky setup with modify-or-spawn, read-merge-write semantics, plus clear color, and the per-frame reads of the resolved lights. Identity is the component, never the entity name: the sun is the `Light` the renderer's snapshot names as the directional holder, the ambient is the light-role component of kind "ambient", and the sky is the entity carrying a sky-role component. Name-based lookup, word resolution, and sky-material orchestration (presets, material swap) live in the `lighting` toolbox. `sun` and `ambient` configuration patch the scene's resolved sun / ambient light components, spawning a carrying entity when the scene has none. A partial update (e.g. only `intensity`) reads the component's current fields first and merges the given fields on top, so unspecified fields keep their authored values instead of resetting to a default. `sky` writes the sky entity's ProceduralSky component the same way — any of its fields, plus `enabled = false` to remove the sky component. ## Types - `SunOpts` — `{ direction?, color?, intensity?, castsShadows? }`. - `AmbientOpts` — `{ color?, intensity? }`. - `ProceduralSkyOpts` — ProceduralSky component fields, plus `enabled = false` to remove the sky. - `SetupOpts` — `{ sun?, ambient?, sky?, clearColor? }`. - `SetupResult` — `{ sun?, ambient?, sky? }`, the entity ids each provided section resolved to. - `Sun` — `{ direction, color, intensity, castsShadows, entityId? }`. - `Ambient` — `{ color, intensity, entityId? }`. - `LightRow` — one punctual light as the renderer resolved it. ## Exports Writes — each takes the opts above and answers with the entity the light resolved to: - `M.setSun(opts: SunOpts) -> string` — set the scene's sun, returning its entity id. - `M.setAmbient(opts: AmbientOpts) -> string` — set the scene's ambient term, returning its entity id. - `M.applySetup(opts: SetupOpts) -> SetupResult` — apply a lighting setup in one call. All fields optional — only provided fields change. `clearColor` is `{r, g, b}`. - `M.setProbeVolume(key: string, volume)` / `M.removeProbeVolume(key: string)` — publish or retract a baked irradiance probe volume. Reads — each takes no arguments, and answers from the resolved lighting state at a cost independent of scene size: - `M.sun() -> Sun` — the sun the frame is shaded by. - `M.ambient() -> Ambient` — the ambient term the frame is shaded by. - `M.lightRows() -> { LightRow }` — every punctual light the renderer resolved this frame. Identity: - `M.lightKind(componentType: string, component: any?) -> string?` — the kind a light-role component names. - `M.lightOfKind(entityId: string, kind: string) -> any` — the light-role component of that kind on one entity. ## Usage ```luau local lighting = require("@builtin::modules.api.engine.lighting") lighting.setSun({ direction = { 0.3, -1, 0.2 }, intensity = 2.0 }) lighting.setAmbient({ intensity = 0.3 }) lighting.applySetup({ sun = { direction = { 0.3, -1, 0.2 }, intensity = 2.0 }, ambient = { intensity = 0.3 }, sky = { timeOfDay = 14 }, }) local sun = lighting.sun() print(sun.intensity, sun.entityId) ``` A reader takes no arguments and a setter takes the opts table, so `lighting.sun(opts)` is refused with the name of the call that applies it.

# 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).

# areaLights system Lights that emit from a surface rather than from a point. Every screen, neon sign, glowing window, ceiling panel and lantern face is an area emitter. Standing a point light in the middle of one gets the brightness roughly right and the character completely wrong: a point puts a pinpoint reflection on the floor and a radial falloff on the wall, where the real thing puts the shape of the emitter and a falloff that follows its extent. ## Using it An emitter that should follow an entity's face is a component: ```lua local id = entity.spawn("tv").id entity(id).component.add("SurfaceLight", { width = 2.0, height = 1.2, face = "front", -- front | back | up | down | left | right intensity = 6.0, range = 12, }) ``` The rectangle turns with the entity, so a tilted screen lights the direction it actually points. Every field is live, and an `intensity` of 0 removes the light. For code placing emitters directly: ```lua local surfaceLight = require("@builtin::systems.areaLights.surfaceLight") surfaceLight.set("strip", { position = { 0, 5, -12 }, right = { 1, 0, 0 }, up = { 0, 1, 0 }, width = 0.6, height = 7, color = { 1, 0.72, 0.35 }, intensity = 5, }) surfaceLight.remove("strip") surfaceLight.configure({ diffuse = 1, specular = 0.5 }) surfaceLight.clear() ``` ## What the knobs do | field | effect | |---|---| | `width` / `height` | Size of the emitting rectangle, world units. The shape of the light is the shape of this. | | `face` | Which way the entity emits. | | `range` | How far the light carries, with a smooth cutoff at the end. | | `intensity` | Brightness. 0 removes the light. | | `colorR` / `colorG` / `colorB` | Emitter colour. | | `offset` | Distance the rectangle sits proud of the entity's origin, along the face's normal. | | `diffuse` / `specular` | Scales on the two terms — the wash across a surface, and the reflected shape of the emitter. | Shape is the point. A wide panel puts a broad pool on the floor; a narrow strip puts a narrow elongated one. That difference is not reachable with a point light at any brightness. At most 32 emitters are held at once, because the shader loops every light for every pixel. ## How it renders `areaLighting.renderFeature` runs one compute pass after lighting. Diffuse is the exact irradiance of the quad — Lambert's formula over its four edges — which matters where a point approximation fails hardest: a wide emitter close to a wall. Specular uses the representative point on the rectangle nearest the reflection ray, with the lobe widened to cover the emitter's solid angle and its peak scaled down to match, so a large emitter reads broader rather than brighter. ## Files ``` areaLights.package/ SurfaceLight.component/ -- an emitter on an entity's face surfaceLight.module/ -- the emitter registry and scales areaLighting.renderFeature/ -- the compute pass ```

# ambientOcclusion system Screen-space ambient occlusion — the contact darkening in corners, creases and where objects meet. Without it, every concave region is lit exactly like a flat one: a box resting on a floor has no seam, a corner is as bright as the wall, and an untextured scene reads as plastic. Occlusion is the cheapest shading cue there is per millisecond, because it needs no extra geometry pass — only the depth and normal the frame already produced. Three techniques are shipped. All three answer the same question — what fraction of the hemisphere above this pixel is visible — and all three cost the same taps to answer it. ## Using it The scene's occlusion is a component — author it once and it persists with the scene: ```lua local id = entity.spawn("ambient_occlusion").id entity(id).component.add("AmbientOcclusion", { technique = "gtao", -- ssao | hbao | gtao intensity = 0.9, -- how far the darkening goes, 0..1 radius = 1.5, -- world-space reach quality = "high", -- low | medium | high | ultra }) ``` Every field is live: edit one in the inspector and the shading follows. Setting `intensity` to 0 turns it off without losing the rest. For code that adjusts occlusion at runtime — a quality slider, a cutscene — reach for the module directly (same options, no component): ```lua local ao = require("@builtin::systems.ambientOcclusion.ao") ao.set({ technique = "hbao", intensity = 0.9 }) -- any subset; the rest is kept ao.get() -- the settings in force ao.techniques() -- the three, each with what it does ao.qualityLevels() -- the sampling shape each level costs ao.active() -- is the pass running ao.clear() -- off, settings kept ``` ## The three techniques | technique | what it measures | |---|---| | `ssao` | Taps scattered over a disk, each weighed on its own: how far the neighbour rises above the tangent plane, over how far away it is. | | `hbao` | One horizon per direction — a ray marched outward until it finds the steepest thing along it — averaged as sines. | | `gtao` | The cosine-weighted arc between the two horizons of a slice, in closed form. This is the visibility the other two estimate. | They are scaled to agree. A point in a right-angle corner sees exactly half the hemisphere, and each technique is normalised so it reads that corner as half: | technique | flat plane | right-angle corner | occlusion | |---|---|---|---| | `ssao` | 1.000 | 0.566 | 0.434 | | `hbao` | 1.000 | 0.592 | 0.408 | | `gtao` | 1.000 | 0.594 | 0.406 | That is what lets `intensity` mean the same thing whichever technique is selected, so switching one for another changes how the estimate is made rather than how dark the scene gets. ## What the knobs do | field | effect | |---|---| | `technique` | Which estimator runs: `ssao` \| `hbao` \| `gtao`. | | `intensity` | How far the darkening goes, in [0, 1]. 0 turns it off and releases the pass. | | `radius` | World-space reach — roughly "how big is a crease worth darkening". Constant in world space, so it does not swell as the camera approaches. | | `power` | Contrast curve on the visibility term. Above 1 deepens the dark end. | | `thickness` | World-space thickness assumed for an occluder, so a thin foreground object stops occluding everything behind it out to the full radius. | | `bias` | How far a neighbour must rise above the surface before it counts as an occluder rather than as the surface itself, in [0, 1]. Raise it if a flat surface shades itself in patches; lower it if fine creases disappear. | | `quality` | Sampling shape. See the table below. | | quality | slices × steps | taps per pixel | resolution | |---|---|---|---| | `low` | 2 × 3 | 12 | half | | `medium` | 3 × 4 | 24 | half | | `high` | 4 × 6 | 48 | full | | `ultra` | 6 × 8 | 96 | full | Every technique spends the same budget: `slices × steps × 2` taps. `gtao` walks each slice both ways, `hbao` treats each of the two directions as its own ray, and `ssao` takes that many independent taps of the disk. The lower two levels compute occlusion on a half-resolution grid — a quarter of the pixels, each still costing its level's taps. Occlusion is low-frequency almost everywhere, and the filter that removes the sampling noise lifts the coarse grid back to the frame in the same pass, weighting each texel by the depth where it sits so silhouettes survive the upsample. What a half-resolution grid loses is the innermost pixel of a sharp crease; everything wider than a couple of pixels comes back the same. ## How it renders One compute pass after lighting writes the per-pixel visibility, a second filters it and multiplies it into the frame, and a blit puts the result on screen. The filter is depth-aware: a plain blur would bleed occlusion across silhouettes, so each tap is weighted by how close its depth is to the centre pixel's. Every technique jitters its sampling by a per-pixel offset, which trades banding for noise; the filter is the half of that trade that removes the noise. Depth, normal and camera come from the render target being drawn (`@scene.depth`, `@scene.normal`, `@frame.camera`), so the result is correct in offscreen captures and render-to-texture cameras at their own resolutions, not only the live viewport. Sky pixels are passed through — there is no surface to occlude. The normal buffer is the deferred G-buffer, so this needs the deferred path (the default). ## Seeing the occlusion on its own While occlusion is running, `ambientOcclusion` is a capture view: the filtered visibility with no scene colour, white where the hemisphere is open and dark where it is closed. ``` capture { pass = "ambientOcclusion" } ``` It is the fastest way to tell a shading problem from an occlusion one, and to compare two techniques or two `radius` values without the lighting in the way. ## Files ``` ambientOcclusion.package/ AmbientOcclusion.component/ -- the scene's occlusion, authored and persisted ao.module/ -- ao.set / .get / .techniques / .qualityLevels / .active / .clear aoShared.module/ -- the prelude, filter and passes the techniques share ssao.renderFeature/ -- taps weighed on their own hbao.renderFeature/ -- one horizon per direction gtao.renderFeature/ -- the arc between two horizons ```

# 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.