Physics

Phase-6 adoption (manim-physics-inspired). Analytic fields/waves are dependency-free; rigid-body uses a built-in engine by default (pluggable).

Electromagnetic fields (analytic)

import { ElectricField, MagneticField } from "ecmanim";
scene.add(new ElectricField([
  { position: [-2, 0, 0], magnitude: 1 },   // + charge
  { position: [2, 0, 0], magnitude: -1 },    // − charge
]));
scene.add(new MagneticField([{ position: [0, 0, 0], magnitude: 1 }])); // out-of-plane current

electricFieldFunc(charges) / magneticFieldFunc(currents) return the raw field functions (Coulomb; B = I·(ẑ×r)/|r|²) for use anywhere a (p) → vector is wanted.

Waves

import { LinearWave, StandingWave } from "ecmanim";
scene.add(new LinearWave({ amplitude: 1, wavelength: 3, frequency: 1 }));   // y = A·sin(kx − ωt)
scene.add(new StandingWave({ amplitude: 1, wavelength: 4 }));               // y = A·sin(kx)·cos(ωt)

The wave advances automatically (an updater increments its time). setTime(t) sets it explicitly.

Rigid-body

import { physics, Pendulum } from "ecmanim";
const engine = physics(scene, { gravity: [0, -9.8, 0], floor: -3, restitution: 0.6 });
engine.addBody(ball, { velocity: [1, 0, 0] });   // falls + bounces off the floor
scene.add(new Pendulum({ length: 2, initialAngle: 0.9 })); // ODE-integrated each frame

The default SimpleEngine (semi-implicit Euler + gravity + floor collision) is dependency-free and stepped per frame. Pendulum integrates θ'' = −(g/L)·sinθ directly (no engine needed).

SimpleEngine limitations — know what you’re getting:

• Rotation is kinematic only: addBody(mob, { angularVelocity: 2 }) spins a body at a constant rate about its center, but collisions never impart or change spin (no friction impulses, no moment of inertia).
• The only collision is the floor plane (with restitution). There is no body–body collision, no walls, no arbitrary shapes, no constraints/joints.
• Integration is plain semi-implicit Euler — fine for demos, not for stacked or resting-contact scenes (objects will jitter or sink).

For anything beyond “things fall and bounce”, ecmanim ships two real engines built on Rapier — a 2D and a 3D backend — both implementing the same PhysicsEngineLike (step(dt)) contract, so they drop into a scene the same way physics() does. They’re optional dependencies imported from subpaths, so the core bundle never pays for the WASM. (You can still implement PhysicsEngineLike around any other engine, e.g. planck.js, yourself.)

2D rigid-body (Rapier2D)

npm i @dimforge/rapier2d-compat

import { rapier2d } from "ecmanim/physics/rapier2d";
const engine = await rapier2d(scene, { gravity: [0, -9.8, 0], floor: -3 });
engine.addBody(box, { velocity: [1, 0, 0], angularVelocity: 2 });

Unlike SimpleEngine, boxes actually stack and collide with one another (and with walls) — real contacts, not just a floor plane. 2D lives in ecmanim’s z = 0 plane; a body’s rotation is a scalar angle about Z (matching SimpleEngine’s angularVelocity).

3D rigid-body (Rapier3D)

npm i @dimforge/rapier3d-compat

import { rapier3d } from "ecmanim/physics/rapier3d";
const engine = await rapier3d(scene, { gravity: [0, -9.8, 0], floor: -3 });
engine.addBody(cube, { velocity: [1, 0, 0], angularVelocity: [0, 2, 0] });

Genuine 3D rigid-body dynamics — full orientation (bodies tumble, not just spin about one axis), body↔body collision, friction, and arbitrary colliders. addBody infers a collider from the mobject’s bounding box (round types → ball, else cuboid); override with { shape: "ball" | "cuboid" | "capsule", radius, halfExtents }.

Notes for both adapters:

• The factory is async (Rapier initializes its WASM once) — await rapier3d(...) before adding bodies. step(dt) itself is sync, so per-frame stepping via the attached carrier is unchanged.
• Engine options: gravity, floor (a wide fixed slab whose top sits at that y), restitution, friction. Per-body: velocity, angularVelocity, mass, density, restitution, friction, static, shape.
• These use the @dimforge/rapier*-compat builds (WASM inlined), so they load in Node and the browser without bundler plumbing. A browser live-demo is a follow-up (the current browser example copies only dist/).