The 3D system

Scene3D

The root of a 3D branch — an empty stage other 3D nodes build on.

Merge3D

Combines 3D branches into one scene.

Camera3D

A camera in the scene: position/rotation plus film-back (focal, aperture). Render3D renders through it; the viewport shows its frustum.

Card

A plate standing in 3D: an image on a quad at its own aspect. `file` takes a file path — or the NAME of a 2D node to show that branch live.

GeoPrimitive

A geometry primitive (cube, sphere, plane, cylinder) with transform and colour — stand-ins and simple set pieces.

ReadGeo3D

Reads geometry from a .usda or .obj file into the scene.

Transform3D

Transforms 3D geometry: give it target paths (or leave empty for everything upstream) and TRS.

Axis3D

A 3D null/locator — a parent transform other things can follow.

Light3D

A light in the scene — point, spot, distant (sun), rect, or dome (ambient). Authored as a standard UsdLux prim, so the viewport, Render3D, USD export and the Unreal bridge all read the same light. Zero lights in a scene = the neutral headlight rig.

Project3D

Camera projection - the matte-painting workhorse: throws an image from a Camera3D onto target geometry (a subdivided Card, a mesh). Freeze the camera on one frame to patch; move the render camera and the projection sticks to the surface.

Render3D

Renders a 3D scene into the comp: point `scene`/`camera` at your 3D branch and a Camera3D, and the CG composites over the bg input as a premultiplied element. `aux` adds depth/N/P/id channels.

VDBRead

Reads a .vdb volume cache (smoke, clouds, fire from FX or a bought pack) into the scene as a standard UsdVol prim. Loads off-thread — the box draws dim while streaming, bright when ready. Rendering the volume itself lands with the volume pass; today you get the placed, pickable bounding box.

VolumeShade

The volume LOOK, separate from the read so one look feeds several VDBReads: density scale, scatter colour, anisotropy (forward/back scattering), emission (fire), self-shadow strength. Without one, VDBRead shows neutral grey smoke.

ParticleSystem3D

A deterministic particle system: sparks, dust, rain, embers. Emits from a point, card, sphere or box; gravity, drag and curl-noise turbulence move them; size and colour ramp over each particle's life. The sim is bit-identical every time — the same seed and frame give the same answer whether you played there or scrubbed there, so a re-render is a re-render. Particles are authored as a standard USD Points prim, so they carry velocities and per-particle ids for motion blur and id passes.

PointCloud3D

A solved camera track's 3D point cloud: each tracked feature's reconstructed position as a small marker. Scene+ creates one; snap cards and geometry to it.

SplatRead

Reads a gaussian-splat capture (.ply in the 3DGS layout, .splat, or .spz) into the scene: a captured location as millions of soft elliptical blobs, with parallax and view-dependent colour. Loads off-thread — the box draws dim while streaming, then the splats render in the viewport and Render3D, sorted and alpha-blended, depth-composited against cards and geometry. `color_space` declares what the trainer baked (sRGB is usual; a washed-out or crunchy capture is almost always this knob). `budget` caps drawn splats by importance and SAYS so in the HUD. `cluster_tolerance` sets the spatial cluster size used for crypto ids, groups and normal smoothing (0 = automatic). RELIGHT (§4): `relight`=lights turns on the dynamic Light3D loop — `ambient` dims the capture-day lighting baked into the splats and the scene's lights add your own key/fill/rim on top (`light_gain` scales them, `exposure` in stops scales the whole). This is relighting a captured location, which no other compositor does. CLEANUP (§5.4): floater_removal drops the debris clouds every capture has (a statistical outlier pass — the raw scene bounds are usually dominated by them); opacity_floor culls near-transparent splats.

SplatFx

Directs a gaussian-splat capture with a FIELD over its splats (spec §5) — the difference between a viewer and comp. crop: keep or carve a box/sphere region, feathered into a soft opacity falloff (splats feather beautifully). dissolve: fade opacity by a noise/distance/axis field, optionally shrinking splats to nothing (the assemble-the-hologram look). warp: push splats along a field — swirl, drift, wind. shade: tint + gamma the base colour. matte: project a 2D matte (a Roto, a Crucible key, any branch) through a camera and dissolve the splats it covers — the cross-system trick nothing else can do. Dissolve/warp/shade take an optional REGION (box/sphere) so the effect hits one object, not the whole scene. Chain several; each appends to the set. Cleanup (floater removal, opacity floor) lives on the SplatRead node.

Prune3D

Hides or deactivates prims by path — trim the scene without deleting nodes.

Display3D

Overrides how prims draw in the viewport (wireframe, points, bbox…) without touching the render.