Function OutputPolygon

Filters/Modeling/vtkContourLoopExtraction.cxx:120–197

March along connected lines to the end----------------------------------

// March along connected lines to the end----------------------------------
void OutputPolygon(LoopPointType& sortedPoints, vtkPoints* inPts, vtkCellArray* outLines,
  vtkCellArray* outPolys, int loopClosure)
{
  // Check to see that last point is the same as the first. Such a loop is
  // closed and can be directly output. Otherwise, check on the strategy
  // for closing the loop and close as appropriate.
  vtkIdType num = static_cast<vtkIdType>(sortedPoints.size());
  if (sortedPoints[0].Id == sortedPoints[num - 1].Id)
  {
    --num;
    sortedPoints.erase(sortedPoints.begin() + num);
  }

  else if (loopClosure == VTK_LOOP_CLOSURE_ALL)
  {
    // do nothing and it will close between the first and last points
  }

  // If here we assume that the loop begins and ends on the given bounding
  // box (i.e. the boundary of the data). Close the loop by walking the
  // bounding box in the plane defined by the Normal plus the loop start
  // point.
  else if (loopClosure == VTK_LOOP_CLOSURE_BOUNDARY)
  {
    // First check the simple case, complete the loop along horizontal or
    // vertical lines (assumed on the boundary).
    double p0[3], p1[3], delX, delY;
    inPts->GetPoint(sortedPoints[0].Id, p0);
    inPts->GetPoint(sortedPoints[num - 1].Id, p1);
    delX = fabs(p0[0] - p1[0]);
    delY = fabs(p0[1] - p1[1]);

    // if no change in either the x or y direction just return, the loop will complete
    if (delX < FLT_EPSILON || delY < FLT_EPSILON)
    {
      // do nothing loop will complete; points are along same (horizontal or vertical) boundary
      // edge
    }

    // Otherwise check if the points are on the "boundary" and then complete the loop
    // along the shortest path around the boundary.
    else
    {
      return;
    }
  }

  // Don't close
  else // loopClosure == VTK_LOOP_CLOSURE_OFF
  {
    return;
  }

  // Return if not a valid loop
  if (num < 3)
  {
    return;
  }