Function extractFrame

Web/script.js:293–395

(folderId, frameNum, baseDir = "")

  watermarkLoaded = true;
};
async function extractFrame(folderId, frameNum, baseDir = "") {
  const groupIndex = Math.floor((folderId - 1) / 10);
  const requestKey = `${baseDir}/${groupIndex}/${folderId}/${frameNum}`;

  return RequestController.enqueue(requestKey, async () => {
    try {
      if (!baseDir) {
        throw new Error("Base directory is required");
      }

      const indexData = await indexCache.get(groupIndex, baseDir);

      const dataView = new DataView(indexData);
      let offset = 0;

      const gridW = dataView.getUint32(offset, true);
      offset += 4;
      const gridH = dataView.getUint32(offset, true);
      offset += 4;
      const folderCount = dataView.getUint32(offset, true);
      offset += 4;
      offset += folderCount * 4;
      const fileCount = dataView.getUint32(offset, true);
      offset += 4;

      let left = 0;
      let right = fileCount - 1;
      let startOffset = null;
      let endOffset = null;

      while (left <= right) {
        const mid = Math.floor((left + right) / 2);
        const recordOffset = offset + mid * 16;
        const currFolder = dataView.getUint32(recordOffset, true);
        const currFrame = dataView.getUint32(recordOffset + 4, true);
        const currFileOffset = Number(
          dataView.getBigUint64(recordOffset + 8, true),
        );

        if (currFolder === folderId && currFrame === frameNum) {
          startOffset = currFileOffset;
          if (mid < fileCount - 1) {
            endOffset = Number(dataView.getBigUint64(recordOffset + 24, true));
          }
          break;
        } else if (
          currFolder < folderId ||
          (currFolder === folderId && currFrame < frameNum)
        ) {
          left = mid + 1;
        } else {
          right = mid - 1;
        }
      }

      if (startOffset === null) {
        throw new Error(`Frame ${frameNum} not found in folder ${folderId}`);
      }