@frsource/babylon-box3d

A Babylon.js Physics V2 plugin backed by box3d-wasm, a WebAssembly build of Erin Catto's Box3D rigid body engine.

It follows the same shape as @babylonjs/havok's HavokPlugin: a class implementing IPhysicsEnginePluginV2 that can be passed straight to scene.enablePhysics(gravity, plugin).

Live demo →

Installation

npm i @frsource/babylon-box3d box3d-wasm

@babylonjs/core is a peer dependency -- install whichever version (^9.0.0) your project already uses.

Usage

import Box3D from 'box3d-wasm';
import { Box3DPlugin } from '@frsource/babylon-box3d';

const box3d = await Box3D();
const plugin = new Box3DPlugin(box3d);

scene.enablePhysics(new Vector3(0, -9.81, 0), plugin);

Coverage

Box3D's JS bindings are narrower than Havok's, so a few corners of IPhysicsEnginePluginV2 are best-effort:

• Shapes: box, sphere, capsule and convex hull are fully supported. CONTAINER shapes are supported by attaching every child shape to the same box3d body. MESH, HEIGHTFIELD and CYLINDER are not supported by box3d-wasm and throw a descriptive error.
• Bodies: only a single instance per PhysicsBody is supported (no thin-instance batching) — initBodyInstances falls back to treating the mesh's own transform as a single body.
• Constraints: BALL_AND_SOCKET, DISTANCE, HINGE, SLIDER/PRISMATIC, LOCK and SIX_DOF (approximated with a weld/motor joint) map onto box3d's spherical/distance/revolute/prismatic/weld joints. Per-axis limit APIs are best-effort since box3d joints are already axis-specific (unlike Havok's generic 6-DOF constraint).
• raycast only returns the closest hit per query (box3d-wasm exposes castRayClosest, not a multi-hit sweep).

Raw box3d access

Some box3d-wasm features have no equivalent in Babylon's IPhysicsEnginePluginV2 -- most notably its car wheel joint (suspension + steering + drive in one joint), used for vehicles rather than generic constraints, plus its filter and parallel joints. Box3DPlugin exposes the underlying world: Box3DWorld publicly for exactly this: create bodies through Babylon as usual, then reach plugin.world.createWheelJoint(bodyA, bodyB, options) (or createFilterJoint/createParallelJoint) directly.

box3d-wasm ships no bundled types at all, so this package's box3d-wasm.d.ts declares only what Box3DPlugin itself uses. extraJoints.d.ts augments it with the wheel/filter/parallel joint surface (verified present in the compiled [email protected] binary by instantiating it and inspecting the live prototypes) for consumers who need raw access. Both are ambient module declarations; index.ts pulls them into the program via triple-slash references, so any package that does import { Box3DPlugin } from '@frsource/babylon-box3d' gets them for free -- no tsconfig.json changes needed, as long as you access box3d-wasm's types only through Box3DPlugin itself (e.g. plugin.world.createWheelJoint(...)). If your own code also writes a direct import ... from 'box3d-wasm', TypeScript won't honor a dependency's augmentation of an already-resolved-but-untyped module for that import (see TS2665) -- copy box3d-wasm.d.ts (and extraJoints.d.ts if you need the wheel/filter/parallel joints) into your own project in that case, the way docs/ here does for the demo.

Demo

docs/ is a standalone Vite + Babylon.js app that ports monteslu/threejs-box3d-demo (originally three.js) onto this plugin, deployed to GitHub Pages from main. See docs/README.md for running it locally.

License

MIT

Copyright (c) 2026-present, Jakub FRS Freisler, FRSOURCE