Unexpected intersection of a polyline

[SeanTreleaven]

I'm trying to intersect a polyline with a polygon but the results are not quite what I would expect.

void Test()
{
   PathD subjectPath;
   subjectPath.push_back(PointD(-69.7, -17.7));
   subjectPath.push_back(PointD(-67.2, -23.3));
   subjectPath.push_back(PointD(-70.5, -31.4));
   subjectPath.push_back(PointD(-74.3, -44.2));
   subjectPath.push_back(PointD(-67.3, -55.7));

   PathsD subjectPaths;
   subjectPaths.push_back(subjectPath);

   PathD clipPath;
   clipPath.push_back(PointD(-73.2, -17.2));
   clipPath.push_back(PointD(-66.9, -27.1));
   clipPath.push_back(PointD(-64.5, -15.4));
   clipPath.push_back(PointD(-73.2, -17.2));

   PathsD clipPaths;
   clipPaths.push_back(clipPath);

   PathsD clippedPaths = BooleanOp(1, 1, subjectPaths, clipPaths, 5);

   for( auto cp : clippedPaths)
   {
      for (auto pt : cp)
      {
         cout << pt.x << "," << pt.y << std::endl;
      }
   }
}

// output
//
// -67.199997,-23.300003
// -69.699997,-17.699997
// -69.349411,-23.250916
// -68.026772,-25.329353
//

// expected output
//
// -69.7, -17.7
// -67.2, -23.3
// -68.026772,-25.329353

Attachments:

1. screenshot1: the interesting portion of the subject polyline
2. screenshot2: the returned result in red
3. screenshot3: my expected result

[AngusJohnson]

Hi Sean.
You have to be careful to properly assign BooleanOp's parameters. You appear to be placing your open subject path where the closed subject path is exected.

Here's the example I sent you via email earlier:

    void Test()
    {
      PathsD subjOpen, clip, sol, solOpen;
      subjOpen.push_back(MakePathD({ 150,100, 190,200, 160,400 }));
      clip.push_back(MakePathD({ 100,100, 250,20, 200,300 }));
      //ClipperD c(5);
      //c.AddOpenSubject(subjOpen);
      //c.AddClip(clip);
      //c.Execute(ClipType::Intersection, FillRule::NonZero, sol, solOpen);
      CPathsD cSubj, cSubjOpen, cClip, cSol, cSolOpen;
      cSubjOpen = CreateCPathsDFromPathsD(subjOpen);
      cClip = CreateCPathsDFromPathsD(clip);
      BooleanOpD(1, 1, nullptr, cSubjOpen, cClip, cSol, cSolOpen, 5);
      solOpen = ConvertCPathsToPathsT<double>(cSolOpen);
      delete(cSubjOpen);
      delete(cClip);
      delete(cSol);
      delete(cSolOpen);
      
      std::cout << "open solution:" << solOpen << std::endl;;
      SvgWriter svg;
      SvgAddOpenSubject(svg, subjOpen, FillRule::NonZero);
      SvgAddClip(svg, clip, FillRule::NonZero);
      SvgAddOpenSolution(svg, solOpen, FillRule::NonZero, false);
      std::string filename = "test.svg";
      SvgSaveToFile(svg, filename, 800, 600);
      System(filename);
    }

[SeanTreleaven]

Hey @AngusJohnson, can you confirm the C++ simple header isn't working? If yes, is there a plan to fix? Thx.

[SeanTreleaven]

I glossed over your commented-out code. Tried that and it does work. Thx.

But note the simple BooleanOp() doesn't take care of this so that part is still an issue.

[SeanTreleaven]

Thanks Angus. I tried swapping the position of the arguments but the result is the same. I'm using the "simple" function interface, which looks like this:

inline PathsD BooleanOp(ClipType cliptype, FillRule fillrule,
    const PathsD& subjects, const PathsD& clips, int precision = 2)

I guess the simple function doesn't work for clipping polylines...? The simple function did work for all my tests of clipping polygons with polygons.

[SeanTreleaven]

Which I see now implies (which is the case) I am not using Clipper2 as a DLL. I'm compiling it into a C++ project that's running on Windows.