# volumetricSky Orchestration backend for the `VolumetricSky.component`. Owns the GPU resources the cloud layer needs (cloud volume, raymarch render target, ping-pong TAA history pair, post-process composite) and exposes a small public surface the component drives every frame. ## Exports - `M.spawn(opts?) -> id` — spawn the singleton sky entity, or configure the one already standing, and return its id. Every weather parameter (`coverage`, `sunDir`, `sunColor`, `sunIntensity`, `windSpeed`, …) is settable at the top level or inside a `preset` sub-table; every `VolumetricSky` component field (`shaderVariant`, `cloudSize`, `taaBlendAlpha`, …) by its own name; `name` names the entity. Parameters left out keep their current values. An option that names neither raises, listing both sets, and leaves no entity behind. A weather parameter takes the shape its default carries — a number, or an array of that many numbers — and a value of another shape raises naming the parameter. - `M.configure(opts) -> boolean` — apply those same weather parameters and component fields to the sky already standing. Returns `false` when none has been spawned. - `M.defaultPreset() -> table` — a fresh copy of the weather configuration a sky spawned with no options carries. The copy is the caller's to edit. - `M.destroy() -> ()` — release every resource `spawn` created. - `M.fillClouds(noiseParams) -> ()` — dispatch the active `cloud_noise_*` shader against the cloud volume. `noiseParams` is the flat table produced by `VolumetricSky.component`'s `snapshotNoiseParams()`. - `M.dispatchRaymarch(renderParams, viewport) -> ()` — dispatch the active `cloud_raymarch_*` shader, blend with history via the TAA pass, and write into the composite target. `renderParams` is the flat table from `snapshotRenderParams()`. - `M.find() -> id?` — return the id of the active VolumetricSky entity, or `nil` if none has been spawned by `M.spawn`. - `M.despawn() -> ()` — despawn the entity `M.spawn` minted (does NOT free GPU resources — call `M.destroy()` for that). - `M.setCoverage(c) / M.setDensity(g) / M.setSun(dir, color, intensity?) / M.setWind(v)` — convenience setters that route through the active component's `public` fields. - `M.reprojectionDepthNdc(camPos, fwd, aabbMin, aabbMax, near, far) -> number` — the NDC z the TAA pass carries history through, taken from where the cloud stands along the centre view ray. A point at range `d` travels `translation / d` across the screen, so this is what keeps a translating camera's history landing on the part of the picture the cloud moved to. ## Usage ```luau -- The component drives this module automatically. Direct M.* use is -- rare; the canonical entry point is attaching VolumetricSky to an -- entity (or loading a preset and passing it to component.add): local sky = entity.spawn("sky") sky.component.add("VolumetricSky", {}) -- Driving the layer by hand instead, a frame at a time. Each dispatch -- creates the resources it needs at the size its own arguments name — -- the cloud volume from `noiseParams.cloudSize / cloudHeight`, the -- render target and composite from the viewport: local Sky = require("@builtin::systems.volumetrics.volumetricSky") Sky.fillClouds(noiseParams) Sky.dispatchRaymarch(renderParams, { width = 1280, height = 720 }) ``` ## Notes - `shaderVariant` selects which compute shader pair (`cloud_noise_v3 + cloud_raymarch_v3` / `cloud_noise + cloud_raymarch_v4` / `cloud_noise_v5 + cloud_raymarch_v5`). The module resolves the variant strings to absolute identities — relative paths don't work from a module body (the chunkname retains an `.init` segment that throws off the rsplit-to-parent step in `resolve_relative_dot`). - The cloud volume + history pair are RGBA16F — 256×128×256 ≈ 32 MiB VRAM. Drop to 192/96 via `cloudSize` / `cloudHeight` if tight. - The TAA pass is a single compute dispatch blending current sample with the previous frame's RT through the history pair. Set `taaBlendAlpha = 1.0` to disable while still going through the same code path (useful for benchmarking). - All public setters write through to `VolumetricSky.component`'s `public` fields, which means they replicate as Sync if the component is sync-enabled. Tweaks survive scene reloads as long as the same entity is alive. - `SkyPreset` and its defaults are declared here, and the component declares its `preset` field from them. `M.spawn` / `M.configure` read that same key set to tell a weather parameter from a component field, so a parameter added to the preset reaches the schema and the option routing in one edit.

# volumetrics Volumetric (3D-texture) rendering, end to end, in one package. Built entirely on the engine's generic `compute.*` GPU primitives — no Rust changes are needed to author new volumetric content. ## Layout | Asset | Identity | Role | |---|---|---| | `Volume.component` | `@builtin::systems.volumetrics.Volume` | Attach a 3D voxel texture to an entity; raymarches it through the entity's transform AABB. | | `VolumetricSky.component` | `@builtin::systems.volumetrics.VolumetricSky` | Singleton procedural cloud layer with TAA. | | `ParticipatingMedium.component` | `@builtin::systems.volumetrics.ParticipatingMedium` | Mark an entity as fog/smoke/dust that attenuates the light passing through it. | | `mediaTransmittance.module` | `@builtin::systems.volumetrics.mediaTransmittance` | Light-space optical-depth map: the registry, the settings, and the basis the map is built in. | | `mediaShadow.renderFeature` | `@builtin::systems.volumetrics.mediaShadow` | Builds the optical-depth map and attenuates each surface by the density in front of it. | | `volume.module` | `@builtin::systems.volumetrics.volume` | Builders (`noise`/`sphere`/`box`/`wrap`) + the `.zvol` header reader + occupancy + brick paging + the per-entity raymarch dispatch. | | `VolumeSequence.component` | `@builtin::systems.volumetrics.VolumeSequence` | Play an open volume sequence through an entity's transform AABB. | | `volumeSequence.module` | `@builtin::systems.volumetrics.volumeSequence` | A run of `.zvol` frames streamed through a fixed ring of resident volumes. | | `volumeDemos.module` | `@builtin::systems.volumetrics.volumeDemos` | Shared pipeline for the showcase scenes (fill + emissive raymarch + composite). | | `volumetricSky.module` | `@builtin::systems.volumetrics.volumetricSky` | Cloud volume + raymarch + TAA + composite orchestration. | | `shaders/*.shader` | `@builtin::systems.volumetrics.shaders.*` | `volume_raymarch`, `volume_pages`, `volume_pack`, `cloud_noise[_v3/_v5]`, `cloud_raymarch[_v3/_v4/_v5]`, `cloud_taa`. | | `importers/vdb_to_zvol.importer` | (auto-discovered) | `.vdb` → dense `.zvol` via the `openvdb` WASM plugin (procedural fallback when the plugin isn't loaded). | | `presets/cumulus_default.preset` | `@builtin::systems.volumetrics.cumulus_default` | Canonical full `VolumetricSky` weather preset. | | `demo/*.scene` | `@builtin::systems.volumetrics.demo.*` | `sdf_solids`, `smoke_plume`, `nebula`, `godrays`, `zvol_viewer`, `sky`. | ## Path convention — fully-qualified builtin identities Every intra-package reference uses the asset's fully-qualified builtin identity, the same convention every other builtin package follows (cf. `particles.package`): ```luau local Volume = require("@builtin::systems.volumetrics.volume") local Sky = require("@builtin::systems.volumetrics.volumetricSky") local V = require("@builtin::systems.volumetrics.volumeDemos") -- shader identities, e.g. asset.resolve("@builtin::systems.volumetrics.shaders.volume_raymarch") ``` Qualified identities are caller-independent: they resolve identically from a module, a scene entrypoint, or a component. Caller-relative (`.sibling`) requires are deliberately avoided here because the component runtime caller identity is `@builtin::components.<Name>`, so a `.sibling` require from a component resolves against the wrong root. (An earlier revision of this package used a `~volumetrics` package-root alias for relocatability; that alias is not resolvable on current main, so the package uses qualified identities throughout.) ## Usage ```luau -- Per-entity volume. The component resolves the name through `Volume.get`, -- so a volume paged into a brick pool renders from the pool under the same -- name: local Volume = require("@builtin::systems.volumetrics.volume") local cloud = Volume.noise({ name = "cloud", size = 64, scale = 4 }) cloud:buildSparse({ brickSize = 8 }) cloud:releaseDense() entity(id).component.add("Volume", { volumeName = "cloud", density = 6.0 }) -- Procedural sky: local sky = entity.spawn("sky") sky.component.add("VolumetricSky", {}) preset.apply("cumulus_default", { entity = sky.id, component = "VolumetricSky" }) -- VDB import: drop a `.vdb` into the VFS; the importer writes a `.zvol` -- alongside it. Load it with the zvol_viewer demo scene. -- Animated run: one `.zvol` per frame, played through a bounded ring. local Seq = require("@builtin::systems.volumetrics.volumeSequence") Seq.open({ name = "plume", frames = framePaths, resident = 3, fps = 24 }) entity(id).component.add("VolumeSequence", { sequenceName = "plume", density = 6.0 }) ``` ## Plugin dependency The VDB importer delegates real OpenVDB parsing to the `openvdb` plugin in the builtin library, `@builtin::plugins.openvdb`. Without the plugin the importer falls back to a deterministic procedural torus so the pipeline stays functional.

# cloud_raymarch_v5 Production volumetric-cloud raymarcher, v5 (Nubis/Hillaire style): Hillaire multi-scatter octaves (fixes black cloud cores), energy-conserving Beer-Powder-MS lit-edge glow, a 6-offset Wrenninge cone-trace shadow, and a dual-lobe Henyey-Greenstein phase. Reads the cloud volume + occupancy textures and writes the lit raymarch result. Bindings (see bindings.yaml): `clouds` (texture3d), `occupancy` (texture3d), `cloud_smp` (sampler), `out_tex` (storage2d rgba16f), `U` (read `array<f32>` uniforms). Usage: dispatch by identity with `compute.dispatchEx("@builtin::systems.volumetrics.shaders.cloud_raymarch_v5", ...)` (textures/sampler/storage texture require resource binding, not positional buffers) — it resolves to the shader's stable guid and auto-compiles on first use (no setup).

# cloud_noise Procedural volumetric-cloud noise fill (Schneider/Hillaire style). A low-frequency FBM gives the base blob silhouette, a high-frequency FBM erodes it near the surface for the fluffy cumulus look, plus altitude shaping (round bottom, full middle, anvil top). Writes the 3D cloud density texture. Bindings (see bindings.yaml): `clouds` (storage3d rgba16f — the cloud volume), `U` (read `array<f32>` uniforms). Usage: dispatch by identity with `compute.dispatchEx("@builtin::systems.volumetrics.shaders.cloud_noise", ...)` (storage texture requires resource binding, not positional buffers) — it resolves to the shader's stable guid and auto-compiles on first use (no setup).

# cloud_raymarch Volumetric-sky cloud raymarcher with Frostbite-style lighting: Wrenninge/Hillaire multi-scatter approximation (3 octaves), a 5-sample cone-traced soft self-shadow, and combined Beer-Lambert + Powder so cloud edges glow toward the sun. Reads the cloud volume + occupancy textures and writes the lit raymarch result. Bindings (see bindings.yaml): `clouds` (texture3d), `occupancy` (texture3d), `cloud_smp` (sampler), `out_tex` (storage2d rgba16f), `U` (read `array<f32>` uniforms). Usage: dispatch by identity with `compute.dispatchEx("@builtin::systems.volumetrics.shaders.cloud_raymarch", ...)` (textures/sampler/storage texture require resource binding, not positional buffers) — it resolves to the shader's stable guid and auto-compiles on first use (no setup).

# cloud_noise_v5 Volumetric-cloud noise generator, v5 (Nubis/Schneider style). Builds two foundational noises — Perlin-Worley FBM for the lumpy "cauliflower" base shape and Worley FBM for high-frequency detail erosion — under weather-map control. Writes the 3D cloud density texture. Bindings (see bindings.yaml): `clouds` (storage3d rgba16f — the cloud volume), `U` (read `array<f32>` uniforms). Usage: dispatch by identity with `compute.dispatchEx("@builtin::systems.volumetrics.shaders.cloud_noise_v5", ...)` (storage texture requires resource binding, not positional buffers) — it resolves to the shader's stable guid and auto-compiles on first use (no setup).

# cloud_taa Cloud TAA composite — temporal anti-aliasing for the raymarch output. Reprojects last frame's blended output through the previous view-projection, color-clamps the history to the current sample's neighborhood to suppress ghosting, and exponentially blends the two. Writes both the next-frame history slot and the externally-sampled `scene_volumetric_sky` texture the composite path reads. Reprojection runs through the world point named by uniform `[37]`, the NDC z of the range the cloud stands at along the view ray — `volumetricSky.reprojectionDepthNdc` computes it. The weight the history carries falls to zero across the last `REPROJECT_BORDER_TEXELS` of the reprojected frame, so a pixel whose history lies off the previous frame reaches the raymarch's own output down a gradient rather than across a line. Bindings (see bindings.yaml — slot order must match the Luau dispatch): `cur_tex` (texture2d), `hist_prev` (texture2d), `smp` (sampler), `out_hist` (storage2d rgba16f), `out_scene` (storage2d rgba16f), `U` (read `array<f32>` uniforms). Usage: dispatch by identity with `compute.dispatchEx("@builtin::systems.volumetrics.shaders.cloud_taa", ...)` (textures/sampler/storage textures require resource binding, not positional buffers) — it resolves to the shader's stable guid and auto-compiles on first use (no setup).

# cloud_raymarch_v3 Volumetric-sky cloud raymarcher (Frostbite-style lighting), v3 variant: Wrenninge/Hillaire multi-scatter (3 octaves), 5-sample cone-traced soft shadow, and combined Beer-Lambert + Powder edge glow. Reads the cloud volume + occupancy textures and writes the lit raymarch result. Bindings (see bindings.yaml): `clouds` (texture3d), `occupancy` (texture3d), `cloud_smp` (sampler), `out_tex` (storage2d rgba16f), `U` (read `array<f32>` uniforms). Usage: dispatch by identity with `compute.dispatchEx("@builtin::systems.volumetrics.shaders.cloud_raymarch_v3", ...)` (textures/sampler/storage texture require resource binding, not positional buffers) — it resolves to the shader's stable guid and auto-compiles on first use (no setup).

# cloud_noise_v3 Volumetric-cloud noise fill (Schneider/Hillaire style), v3 variant. Low-frequency FBM base silhouette + high-frequency FBM surface erosion for the billowed cumulus look, with altitude shaping (round bottom, full middle, anvil top). Writes the 3D cloud density texture. Bindings (see bindings.yaml): `clouds` (storage3d rgba16f — the cloud volume), `U` (read `array<f32>` uniforms). Usage: dispatch by identity with `compute.dispatchEx("@builtin::systems.volumetrics.shaders.cloud_noise_v3", ...)` (storage texture requires resource binding, not positional buffers) — it resolves to the shader's stable guid and auto-compiles on first use (no setup).

# cloud_raymarch_v4 Volumetric-sky cloud raymarcher, v4. Adds procedural detail noise computed in-shader on top of the large-scale texture silhouette (removes v3's voxel-grid blockiness) and uses multi-distance shadow sampling (4 geometrically spaced strides) instead of a cone trace. Reads the cloud volume + occupancy textures and writes the lit raymarch result. Bindings (see bindings.yaml): `clouds` (texture3d), `occupancy` (texture3d), `cloud_smp` (sampler), `out_tex` (storage2d rgba16f), `U` (read `array<f32>` uniforms). Usage: dispatch by identity with `compute.dispatchEx("@builtin::systems.volumetrics.shaders.cloud_raymarch_v4", ...)` (textures/sampler/storage texture require resource binding, not positional buffers) — it resolves to the shader's stable guid and auto-compiles on first use (no setup).