import * as EASEL from "easel";

// Group acts as a pivot point. Rotate the pivot to orbit children.
const sun = new EASEL.Mesh(new EASEL.SphereGeometry(1), new EASEL.BasicMaterial({ color: 0xffcc00 }));
scene.add(sun);

const planetPivot = new EASEL.Group();
sun.add(planetPivot);          // pivot inherits sun's world transform

const planet = new EASEL.Mesh(new EASEL.SphereGeometry(0.4), new EASEL.LambertMaterial({ color: 0x4488cc }));
planet.position.x = 4;         // offset from pivot center = orbital radius
planetPivot.add(planet);

const moonPivot = new EASEL.Group();
planet.add(moonPivot);

const moon = new EASEL.Mesh(new EASEL.SphereGeometry(0.15), new EASEL.LambertMaterial({ color: 0xaaaaaa }));
moon.position.x = 1;
moonPivot.add(moon);

// Rotate pivots each frame - children orbit automatically
sun.rotation.y       += 0.1 * dt;
planetPivot.rotation.y += 0.5 * dt;
moonPivot.rotation.y   += 2.0 * dt;