code: protected float findLimitsPoint(ArrayList wall) {
          lineStatus = LINE_STATUS_OK;
          if (yLine < minY || yLine > maxY) {
              lineStatus = LINE_STATUS_OFFLIMITS;
              return 0;
          }
          for (int k = 0; k < wall.size(); ++k) {
              float r[] = (float[])wall.get(k);
              if (yLine < r[0] || yLine > r[1])
                  continue;
              return r[2] * yLine + r[3];
          }
          lineStatus = LINE_STATUS_NOLINE;
          return 0;
      }
docs: Finds the intersection between the <CODE>yLine</CODE> and the column. It will
  set the <CODE>lineStatus</CODE> appropriately.
  
  @param wall the column to intersect
  @return the x coordinate of the intersection