viewer/explode.js

1// Shared explosion math. Pure functions so validate.mjs (Node) and app.js (browser) agree exactly.2// position(t) = assembled + ease(t) * offset — computed from the immutable assembled transform every3// update; nothing accumulates frame to frame.4 5export function easeInOutCubic(t) {6  t = Math.min(1, Math.max(0, t));7  return t < 0.5 ? 4 * t * t * t : 1 - Math.pow(-2 * t + 2, 3) / 2;8}9 10// Document frame [dx, dy(down), dz(rear)]  →  renderer frame [x, y(up), z(toward front)]11export function docVecToScene(v) { return [v[0], -v[1], -v[2]]; }12 13/**14 * Offset (renderer frame) that a component should have at explosion amount t.15 * @param {object} comp       component record (needs .parent, .explode)16 * @param {number} t          0..1 slider amount17 * @param {object} opts       { scope: componentId|null, expandChildren: bool, parentOf: (id)=>comp|undefined }18 * Rules (skill §8): top-level components move in a whole-object explosion; a child's own offset is19 * applied only when its parent is the scope, or when expandChildren is on. Scoped explosion20 * (scope !== null) moves only the scope's direct children; everything else stays assembled.21 */22export function explodedOffset(comp, t, opts) {23  const e = easeInOutCubic(t);24  const off = comp.explode || [0, 0, 0];25  const scaled = docVecToScene(off).map((c) => c * e);26  const zero = [0, 0, 0];27  if (opts.scope) {28    return comp.parent === opts.scope ? scaled : zero;29  }30  if (comp.parent === null) return scaled;31  return opts.expandChildren ? scaled : zero;32}