bubblechambersimart/src/scene/scene.js

/* ============================================================
   scene.js — the single source of truth.
   generateScene(params) returns a pure, renderer-agnostic data
   model. Every renderer (photographic raster, vector SVG/PDF)
   consumes exactly this. Deterministic from params.seed.
   ============================================================ */
import { makeRng, gauss, chance, pick } from '../rng.js';
import { integrateTrack, sampleMomentum, cosmicTrack, sweeperTrack } from './track.js';
import { spawnDeltaSpiral } from './delta.js';
import { spawnVDecay } from './vdecay.js';
import { generateShock } from './shock.js';
import { generateArtifacts } from './artifacts.js';
import { generateInstrument } from './instrument.js';
import { cyrb53 } from '../rng.js';

const LABS = ['BEBC · CERN', 'GARGAMELLE · CERN', '2m HBC · CERN', '82" HBC · SLAC', 'MIRABELLE · IHEP'];

/* One event: a vertex with primaries (+ δ-rays, V-decays for bright events).
   eventZ = depth in the chamber (0 = focal plane), eventAge = how early in the
   exposure it happened (0 = current trigger). Both are stamped on every track the
   event produces so the renderers can vary opacity / size / softness with depth
   and time rather than treating the event as flat. */
function generateOneEvent(params, vertex, intensity, salt, eventZ = 0, eventAge = 0) {
  const rng = makeRng(params.seed, 'event:' + salt);
  const tracks = [];
  const N = Math.max(2, Math.round(params.primaries * (0.45 + intensity * 0.55)));
  const burstConc = 0.3 + params.burst * 0.7;
  const bright = intensity > 0.6;

  for (let i = 0; i < N; i++) {
    const baseAngle = (i / N) * Math.PI * 2;
    const angle = baseAngle + gauss(rng) * 0.4 * (1 - burstConc);
    const p = sampleMomentum(rng, params.pspread);
    const q = chance(rng, 0.5) ? +1 : -1;
    const pts = integrateTrack(
      { x: vertex.x, y: vertex.y, theta: angle, p, q }, params
    );
    tracks.push({ pts, kind: 'primary', weight: intensity, q });

    // δ-rays along bright primaries — abundant, true spirals
    if (bright) {
      const dRng = makeRng(params.seed, salt + ':delta' + i);
      for (let j = 6; j < pts.length; j += 2) {
        if (dRng() < params.deltaRate * 0.12) {
          const dpts = spawnDeltaSpiral(pts[j], params, dRng);
          if (dpts.length > 6) {
            tracks.push({ pts: dpts, kind: 'delta', weight: intensity * 0.9, q: -1 });
          }
        }
      }
    }
  }

  // dense interaction "star": stubby tracks bursting from the vertex, with a
  // few medium prongs reaching further out for a richer burst.
  if (bright && params.burst > 0.15) {
    const sRng = makeRng(params.seed, salt + ':star');
    const nStar = Math.floor(params.burst * 26);
    for (let i = 0; i < nStar; i++) {
      const a = sRng() * Math.PI * 2;
      const medium = sRng() < 0.25;
      const p = medium ? (0.5 + sRng() * 0.7) : (0.13 + sRng() * 0.4);
      const q = chance(sRng, 0.5) ? 1 : -1;
      const pts = integrateTrack(
        { x: vertex.x + gauss(sRng) * 0.012, y: vertex.y + gauss(sRng) * 0.012, theta: a, p, q },
        params, { maxTravel: medium ? 2.6 : 1.1 }
      );
      tracks.push({ pts, kind: 'primary', weight: intensity, q });
    }
  }

  // V-decays only for the brightest (foreground) events
  if (intensity > 0.8) {
    for (let i = 0; i < params.vdecay; i++) {
      const daughters = spawnVDecay(vertex, params, makeRng(params.seed, salt + ':vdecay' + i));
      daughters.forEach(d => {
        if (d.pts.length > 10) tracks.push({ pts: d.pts, kind: 'vdecay', weight: intensity * 0.95, q: d.q });
      });
    }
  }

  // stamp depth & age. Tracks of one interaction fan out in 3D, so they reach a
  // range of depths around the event's base z — this is what gives each trail its
  // own opacity/softness rather than a flat event. δ-rays get extra spread (they
  // scatter off into the volume).
  for (const t of tracks) {
    const spread = t.kind === 'delta' ? 0.45 : 0.3;
    t.z = Math.max(-1.2, Math.min(1.2, eventZ + gauss(rng) * spread));
    t.age = eventAge;
  }
  return tracks;
}

export function generateScene(params) {
  const rng = makeRng(params.seed, 'scene');
  const tracks = [];

  // Foreground event, slightly off-centre — near the focal plane, current trigger
  const fgVertex = { x: (rng() - 0.5) * 0.3, y: (rng() - 0.5) * 0.3 };
  const fgZ = gauss(rng) * 0.12;
  tracks.push(...generateOneEvent(params, fgVertex, 1.0, 'fg', fgZ, 0));

  // Background "history" events — scattered through depth and earlier in time
  const nBg = params.bgEvents || 0;
  for (let i = 0; i < nBg; i++) {
    const bgRng = makeRng(params.seed, 'bg' + i);
    const vx = (bgRng() - 0.5) * 1.7, vy = (bgRng() - 0.5) * 1.7;
    const intensity = params.bgIntensity * (0.5 + bgRng() * 0.5);
    const z = (bgRng() * 2 - 1);                 // anywhere in depth
    const age = 0.25 + bgRng() * 0.7;            // older than the trigger
    tracks.push(...generateOneEvent(
      { ...params, primaries: Math.round(params.primaries * 0.6), vdecay: 0 },
      { x: vx, y: vy }, intensity, 'bg' + i, z, age
    ));
  }

  // Cosmic/transient straight tracks crossing the frame
  const nCosmic = Math.round(params.cosmics || 0);
  for (let i = 0; i < nCosmic; i++) {
    const cRng = makeRng(params.seed, 'cosmic' + i);
    const { pts, q } = cosmicTrack(params, cRng);
    if (pts.length > 8) tracks.push({ pts, kind: 'cosmic', weight: 0.7 + cRng() * 0.3, q, z: gauss(cRng) * 0.5, age: 0.1 + cRng() * 0.3 });
  }

  // Sweepers — big gentle arcs across the frame
  const nSweep = Math.round(params.sweepers || 0);
  for (let i = 0; i < nSweep; i++) {
    const sRng = makeRng(params.seed, 'sweep' + i);
    const { pts, q } = sweeperTrack(params, sRng);
    if (pts.length > 8) tracks.push({ pts, kind: 'sweep', weight: 0.75 + sRng() * 0.25, q, z: gauss(sRng) * 0.4, age: 0.05 + sRng() * 0.2 });
  }

  const shock = generateShock(params, makeRng(params.seed, 'shock'));
  const artifacts = generateArtifacts(params, makeRng(params.seed, 'artifacts'));
  const instrument = generateInstrument(params, makeRng(params.seed, 'instrument'));

  // deterministic archival metadata (so exports are reproducible from the seed)
  const hash = cyrb53(params.seed);
  const ds = parseInt(hash.slice(0, 8), 16);
  const plate = (parseInt(hash.slice(-3), 16) % 999).toString().padStart(3, '0');
  const year = 1971 + (ds % 11);
  const month = 1 + ((ds >> 4) % 12);
  const day = 1 + ((ds >> 8) % 28);
  const exposure = `${year}.${String(month).padStart(2, '0')}.${String(day).padStart(2, '0')}`;
  const lab = pick(makeRng(params.seed, 'lab'), LABS);

  return { tracks, vertex: fgVertex, shock, artifacts, instrument, hash, plate, exposure, lab };
}