Method BuildIntersectList

CPP/Clipper2Lib/src/clipper.engine.cpp:2390–2446

  }

  bool ClipperBase::BuildIntersectList(const int64_t top_y)
  {
    if (!actives_ || !actives_->next_in_ael) return false;

    //Calculate edge positions at the top of the current scanbeam, and from this
    //we will determine the intersections required to reach these new positions.
    AdjustCurrXAndCopyToSEL(top_y);
    //Find all edge intersections in the current scanbeam using a stable merge
    //sort that ensures only adjacent edges are intersecting. Intersect info is
    //stored in FIntersectList ready to be processed in ProcessIntersectList.
    //Re merge sorts see https://stackoverflow.com/a/46319131/359538

    Active* left = sel_, * right, * l_end, * r_end, * curr_base, * tmp;

    while (left && left->jump)
    {
      Active* prev_base = nullptr;
      while (left && left->jump)
      {
        curr_base = left;
        right = left->jump;
        l_end = right;
        r_end = right->jump;
        left->jump = r_end;
        while (left != l_end && right != r_end)
        {
          if (right->curr_x < left->curr_x)
          {
            tmp = right->prev_in_sel;
            for (; ; )
            {
              AddNewIntersectNode(*tmp, *right, top_y);
              if (tmp == left) break;
              tmp = tmp->prev_in_sel;
            }

            tmp = right;
            right = ExtractFromSEL(tmp);
            l_end = right;
            Insert1Before2InSEL(tmp, left);
            if (left == curr_base)
            {
              curr_base = tmp;
              curr_base->jump = r_end;
              if (!prev_base) sel_ = curr_base;
              else prev_base->jump = curr_base;
            }
          }
          else left = left->next_in_sel;
        }
        prev_base = curr_base;
        left = r_end;
      }
      left = sel_;
    }
    return intersect_nodes_.size() > 0;
  }