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

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(); }
    });
  });
}

// --- 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', onProgress } = opts;
  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 {
    const total = Math.max(1, Math.round(timeline.duration * fps));
    const { renderId } = await postJSON('/render/begin', { name, fps, width, height });

    const inflight = new Set();
    for (let f = 0; f < total; f++) {
      timeline.step(f);                 // seek(f/fps)+evaluate — never wall-clock
      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 p = fetch(`/render/${renderId}/frame/${f}`, { method: 'POST', body: blob })
        .then(r => { if (!r.ok) throw new Error(`frame ${f}: ${r.status}`); })
        .finally(() => inflight.delete(p));
      inflight.add(p);
      onProgress?.(f + 1, total);
    }
    await Promise.all(inflight);

    await postJSON(`/render/${renderId}/end`, {});
    let st;
    do { await sleep(500); st = await (await fetch(`/render/${renderId}/status`)).json(); }
    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`;
  } finally {
    stage.renderer.setPixelRatio(prev.dpr);
    stage.renderer.setSize(prev.w, prev.h, false);
  }
}

// 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);
}

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}`);
  return r.json();
}