Superfluous Point Insertion in Union result

[yongsun-park]

I have been using Clipper and am considering updating to the Clipper2 library.

When I union two simple rectangles as shown below, I get 6 coordinate points instead of 4. While the result is not incorrect, I would like to inquire if it's possible to get a result with 4 coordinate points instead of 6.

rect 1 : (0, 0), (3, 0), (3, 3), (0, 3)
rect 2 : (2, 0), (5, 0), (5, 3), (2, 3)

expect: (0, 0), (5, 0), (5, 3), (0, 3)
result: (0, 0), (3, 0), (5, 0), (5, 3), (2, 3), (0, 3)

Here's the test code:

public static void TwoSquareUnionTest()
    {
      const int size = 10;
      const int w = 800, h = 600;
      FillRule fillrule = FillRule.NonZero;

      Path64 rect1 = Clipper.MakePath(new int[] { 0, 0, 3, 0, 3, 3, 0, 3 });
      Path64 rect2 = Clipper.MakePath(new int[] { 2, 0, 5, 0, 5, 3, 2, 3 });
      Paths64 subjects = new(), solution;

      solution = Clipper.Union(new Paths64() { rect1 }, new Paths64() { rect2 }, FillRule.EvenOdd);

      SvgWriter svg = new SvgWriter();
      SvgUtils.AddSubject(svg, rect1);
      SvgUtils.AddClip(svg, rect2);
      SvgUtils.AddSolution(svg, solution, true);
      string filename = @"..\..\..\TwoSquareUnion.svg";
      SvgUtils.SaveToFile(svg, filename, fillrule, w, h, 10);
      ClipperFileIO.OpenFileWithDefaultApp(filename);
    }

[gigglesun]

there is two extra colinear points in the result.

     Paths64 subject;
     subject.push_back(MakePath({ 0, 0, 3, 0, 3, 3, 0, 3 }));
     subject.push_back(MakePath({2, 0, 5, 0, 5, 3, 0, 3}));

     Clipper64 clipper;
     clipper.AddSubject(subject);

     Paths64 result;
     clipper.Execute(ClipType::Union, FillRule::Positive, result);
     std::cout << result << std::endl; // 3,0 , 5,0 , 5,3 , 2,3 , 0,3 , 0,0

maybe clipper lib could handle or do post handle this since it's not diffcult to remove colinear points.

BTW, here should use Positve filling rule to get the result in C++, if use EvenOdd filling rule, the result would be:
2,0 , 2,3 , 0,3 , 0,0
5,3 , 3,3 , 3,0 , 5,0

[yongsun-park]

When you add two rectangles to the Subject and perform a Union with EvenOdd, the result will still show two rectangles. In my case, I set rectangles for both Subject and Clip separately and did a Union with EvenOdd, and in that case, the result comes out as a single rectangle.

Below is the implementation of the Union function I used.

    public static Paths64 Union(Paths64 subject, Paths64 clip, FillRule fillRule)
    {
      return BooleanOp(ClipType.Union, subject, clip, fillRule);
    }

    public static Paths64 BooleanOp(ClipType clipType,
      Paths64? subject, Paths64? clip, FillRule fillRule)
    {
      Paths64 solution = new Paths64();
      if (subject == null) return solution;
      Clipper64 c = new Clipper64();
      c.AddPaths(subject, PathType.Subject);
      if (clip != null)
        c.AddPaths(clip, PathType.Clip);
      c.Execute(clipType, fillRule, solution);
      return solution;
    }