SCENEGOD/scenegod/web/render.js

// render.js — draft + final video capture (Lane C, PLAN §4.3 / C-server §C5).
// Talks to Stage/Timeline through their public APIs only. No three.js import.
//
//   draftRecord(stage, timeline)       -> Promise<Blob>  quick webm via MediaRecorder
//   finalRender(stage, timeline, opts) -> Promise<url>   deterministic PNG->ffmpeg mp4
//
// The pieces finalRender is built from are exported too — web/film.js drives the
// same loop once per shot of a multi-shot sequence (M8-C), so the frame-post path
// exists exactly once.
// All URLs are RELATIVE: the app serves at / locally and /scenegod/ in prod.

const sleep = ms => new Promise(r => setTimeout(r, ms));

// --- draft: record the live canvas while the timeline plays, once through ----
export function draftRecord(stage, timeline, { fps = 30, mimeType = 'video/webm' } = {}) {
  const stream = stage.renderer.domElement.captureStream(fps);
  const rec = new MediaRecorder(stream, MediaRecorder.isTypeSupported(mimeType) ? { mimeType } : {});
  const chunks = [];
  rec.ondataavailable = e => e.data.size && chunks.push(e.data);
  return new Promise((resolve, reject) => {
    rec.onstop = () => resolve(new Blob(chunks, { type: rec.mimeType || 'video/webm' }));
    rec.onerror = reject;
    rec.start();
    timeline.seek(0);
    timeline.play();
    const stop = timeline.onTick(t => {
      if (t >= timeline.duration) { timeline.pause(); rec.stop(); if (typeof stop === 'function') stop(); }
    });
  });
}

// --- render-session primitives (shared with film.js) -------------------------

// Render at exactly width x height, then put the viewport back however fn ends.
export async function withRenderSize(stage, width, height, fn) {
  const canvas = stage.renderer.domElement;
  const prev = { w: canvas.width, h: canvas.height, dpr: stage.renderer.getPixelRatio() };
  stage.renderer.setPixelRatio(1);
  stage.renderer.setSize(width, height, false);   // false = don't touch CSS size
  try { return await fn(); }
  finally {
    stage.renderer.setPixelRatio(prev.dpr);
    stage.renderer.setSize(prev.w, prev.h, false);
  }
}

export async function beginRender({ name = 'scene', fps = 30, width = 1920, height = 1080 } = {}) {
  return postJSON('render/begin', { name, fps, width, height });
}

// Step [from, to) on the timeline and post those frames as 0..n-1 of renderId.
// Deterministic: timeline.step() is seek+evaluate, never wall-clock.
export async function captureFrames(stage, timeline, { renderId, from = 0, to, onProgress } = {}) {
  const canvas = stage.renderer.domElement;
  const total = Math.max(0, to - from);
  const inflight = new Set();
  for (let f = from; f < to; f++) {
    timeline.step(f);
    if (stage.syncVideos) await stage.syncVideos(timeline.time);  // M6 video plates: seek + wait 'seeked'
    stage.renderActiveCamera(null);   // draw active cam (or director cam) to main canvas
    const blob = await new Promise(res => canvas.toBlob(res, 'image/png'));
    while (inflight.size >= 4) await Promise.race(inflight);      // backpressure: <=4 in flight
    const n = f - from;
    const p = fetch(`render/${renderId}/frame/${n}`, { method: 'POST', body: blob })
      .then(r => { if (!r.ok) throw new Error(`frame ${n}: ${r.status}`); })
      .finally(() => inflight.delete(p));
    inflight.add(p);
    onProgress?.(n + 1, total);
  }
  await Promise.all(inflight);
  return total;
}

export async function endRender(renderId, audio = []) {
  return postJSON(`render/${renderId}/end`, { audio });   // scene audio[] muxed by ffmpeg
}

export async function pollRender(renderId, every = 500) {
  let st;
  do { await sleep(every); st = await getJSON(`render/${renderId}/status`); }
  while (st.state === 'queued' || st.state === 'encoding');
  if (st.state !== 'done') throw new Error('encode failed: ' + (st.log || st.state));
  return `render/${renderId}/out.mp4`;
}

// --- final: step frame-by-frame (deterministic), upload PNGs, ffmpeg encode ---
export async function finalRender(stage, timeline, opts = {}) {
  const { fps = 30, width = 1920, height = 1080, name = 'scene', audio = [], onProgress } = opts;
  return withRenderSize(stage, width, height, async () => {
    const total = Math.max(1, Math.round(timeline.duration * fps));
    const { renderId } = await beginRender({ name, fps, width, height });
    await captureFrames(stage, timeline, { renderId, from: 0, to: total, onProgress });
    await endRender(renderId, audio);
    return pollRender(renderId);
  });
}

// trigger a browser download of a blob or url (draft webm / final mp4)
export function download(blobOrUrl, filename) {
  const a = document.createElement('a');
  a.href = typeof blobOrUrl === 'string' ? blobOrUrl : URL.createObjectURL(blobOrUrl);
  a.download = filename;
  a.click();
  if (typeof blobOrUrl !== 'string') setTimeout(() => URL.revokeObjectURL(a.href), 1000);
}

export async function postJSON(url, body) {
  const r = await fetch(url, { method: 'POST', headers: { 'Content-Type': 'application/json' },
                               body: JSON.stringify(body) });
  if (!r.ok) throw new Error(`${url}: ${r.status} ${await r.text().catch(() => '')}`.trim());
  return r.json();
}

export async function getJSON(url) {
  const r = await fetch(url);
  if (!r.ok) throw new Error(`${url}: ${r.status}`);
  return r.json();
}