function createWorkerProcessors(amount, onmessage) {
    var workers = [];

    if (amount > 0) {
      if (!blobUrl) {
        blobUrl = URL.createObjectURL(
          new Blob(['(' + createPackerProcessor.toString() + ')(true)'], {
            type: 'application/javascript',
          })
        );
      }

      for (var i = 0, worker; i < amount; i++) {
        worker = new Worker(blobUrl);
        if (onmessage) worker.onmessage = onmessage;
        workers.push(worker);
        activeWorkers.push(worker);
      }
    }

    return workers;
  }
Sort rectangles with left-top gravity.

@param {Number} aId
@param {Number} bId
@returns {Number}