code: package org.sunflow.core.bucket;
  
  import org.sunflow.core.BucketOrder;
  
  public class ColumnBucketOrder implements BucketOrder {
      public int[] getBucketSequence(int nbw, int nbh) {
          int[] coords = new int[2 * nbw * nbh];
          for (int i = 0; i < nbw * nbh; i++) {
              int bx = i / nbh;
              int by = i % nbh;
              if ((bx & 1) == 1)
                  by = nbh - 1 - by;
              coords[2 * i + 0] = bx;
              coords[2 * i + 1] = by;
          }
          return coords;
      }
  }