Intersection between open line and polygon doesn't return properly

[JaMan-cmd]

Hello Angus,
I have a problem with intersection
considering the following case. a C shaped polygon and 2 lines. by applying intersection between the line and the polygon, it returns the segment inside the polygon (made in black) but if the line starts or ends very closely to the polygon border, it returns only the segment on the other side. I have been using pathD for my calculations

[AngusJohnson]

  PathsD sub, subo, clp, sol, solo;  
  subo.push_back(MakePathD({ 60.0, 39.5, 120.0,210.0 }));
  subo.push_back(MakePathD({ 120,30, 180,210 }));
  clp.push_back(MakePathD({ 20,20, 220,20, 220,40, 40,40,
    40,200, 220,200, 220,220, 20,220 }));

  ClipperD c;
  c.AddOpenSubject(subo);
  c.AddClip(clp);
  c.Execute(ClipType::Intersection, FillRule::NonZero, sol, solo);

  std::cout << solo << std::endl;

  SvgWriter svg;
  SvgAddSubject(svg, sub, FillRule::NonZero);
  SvgAddOpenSubject(svg, subo, FillRule::NonZero);
  SvgAddClip(svg, clp, FillRule::NonZero);
  SvgAddSolution(svg, sol, FillRule::NonZero, false);
  SvgAddOpenSolution(svg, solo, FillRule::NonZero, false);
  SvgSaveToFile(svg, "c:\\temp\\tmp.svg", 400,300);
  System("c:\\temp\\tmp.svg");

116.484,200 , 120,210
176.664,200 , 180,210
60,39.5 , 60.1797,40
120,30 , 123.336,40

[JaMan-cmd]

Thank you Angus for your reply. I can see that your point is about 0.5 inside the polygon. I'm talking about 0.001 maybe. is there a threshold or accuracy that I need to care about?

[AngusJohnson]

I'm talking about 0.001 maybe. is there a threshold or accuracy that I need to care about?

Sure, that's what ClipperD's optional precision parameter is for.
For example, in my code above, use ...
ClipperD c(4);

[JaMan-cmd]

Ok, that's what I was missing. thank you Angus