Method DoOffset

TheForceEngine/TFE_Polygon/clipper.cpp:3958–4128

//------------------------------------------------------------------------------

void ClipperOffset::DoOffset(double delta)
{
  m_destPolys.clear();
  m_delta = delta;

  //if Zero offset, just copy any CLOSED polygons to m_p and return ...
  if (NEAR_ZERO(delta)) 
  {
    m_destPolys.reserve(m_polyNodes.ChildCount());
    for (int i = 0; i < m_polyNodes.ChildCount(); i++)
    {
      PolyNode& node = *m_polyNodes.Childs[i];
      if (node.m_endtype == etClosedPolygon)
        m_destPolys.push_back(node.Contour);
    }
    return;
  }

  //see offset_triginometry3.svg in the documentation folder ...
  if (MiterLimit > 2) m_miterLim = 2/(MiterLimit * MiterLimit);
  else m_miterLim = 0.5;

  double y;
  if (ArcTolerance <= 0.0) y = def_arc_tolerance;
  else if (ArcTolerance > std::fabs(delta) * def_arc_tolerance) 
    y = std::fabs(delta) * def_arc_tolerance;
  else y = ArcTolerance;
  //see offset_triginometry2.svg in the documentation folder ...
  double steps = pi / std::acos(1 - y / std::fabs(delta));
  if (steps > std::fabs(delta) * pi) 
    steps = std::fabs(delta) * pi;  //ie excessive precision check
  m_sin = std::sin(two_pi / steps);
  m_cos = std::cos(two_pi / steps);
  m_StepsPerRad = steps / two_pi;
  if (delta < 0.0) m_sin = -m_sin;

  m_destPolys.reserve(m_polyNodes.ChildCount() * 2);
  for (int i = 0; i < m_polyNodes.ChildCount(); i++)
  {
    PolyNode& node = *m_polyNodes.Childs[i];
    m_srcPoly = node.Contour;

    int len = (int)m_srcPoly.size();
    if (len == 0 || (delta <= 0 && (len < 3 || node.m_endtype != etClosedPolygon)))
        continue;

    m_destPoly.clear();
    if (len == 1)
    {
      if (node.m_jointype == jtRound)
      {
        double X = 1.0, Y = 0.0;
        for (cInt j = 1; j <= steps; j++)
        {
          m_destPoly.push_back(IntPoint(
            Round(m_srcPoly[0].X + X * delta),
            Round(m_srcPoly[0].Y + Y * delta)));
          double X2 = X;