GraphRow *pPrev;            /* Previous row */

  int idx;                    /* Row index.  First is 1.  0 used for "none" */
  int idxTop;                 /* Direct descendent highest up on the graph */
  GraphRow *pChild;           /* Child immediately above this node */
  u8 isDup;                   /* True if this is duplicate of a prior entry */
  u8 isLeaf;                  /* True if this is a leaf node */
  u8 hasNormalOutMerge;       /* Is parent of at laest 1 non-cherrypick merge */
  u8 timeWarp;                /* Child is earlier in time */
  u8 bDescender;              /* True if riser from bottom of graph to here. */
  i8 iRail;                   /* Which rail this check-in appears on. 0-based.*/
  i8 mergeOut;                /* Merge out to this rail.  -1 if no merge-out */
  u8 mergeIn[GR_MAX_RAIL];    /* Merge in from non-zero rails */
  int aiRiser[GR_MAX_RAIL];   /* Risers from this node to a higher row. */
  int mergeUpto;              /* Draw the mergeOut rail up to this level */

      mask = BIT(pParent->mergeOut);
      for(pLoop=pChild->pNext; pLoop && pLoop->rid!=pParent->rid;
           pLoop=pLoop->pNext){
        pLoop->railInUse |= mask;
      }
    }
  }
  if( !isCherrypick ){
    pParent->hasNormalOutMerge = 1;
  }
  pChild->mergeIn[pParent->mergeOut] = isCherrypick ? 2 : 1;
}

/*
** Compute the maximum rail number.
*/
static void find_max_rail(GraphContext *p){