在区域计算中，有时候需要区域的合并，相交，差值等需求。

这里推荐一个 Clipper2 库， 可以快速高效实现

AngusJohnson/Clipper2: Polygon Clipping and Offsetting - C++, C# and Delphi (github.com)

此库有 C++, C#,  Delphi 版本，都比较好用。

      //C++
      Paths64 subject, clip, solution;
      subject.push_back(MakePath("100, 50, 10, 79, 65, 2, 65, 98, 10, 21"));
      clip.push_back(MakePath("98, 63, 4, 68, 77, 8, 52, 100, 19, 12"));
      solution = Intersect(subject, clip, FillRule::NonZero);

      //C#
      Paths64 subj = new Paths64();
      Paths64 clip = new Paths64();
      subj.Add(Clipper.MakePath(new int[] { 100, 50, 10, 79, 65, 2, 65, 98, 10, 21 }));
      clip.Add(Clipper.MakePath(new int[] { 98, 63, 4, 68, 77, 8, 52, 100, 19, 12 }));
      Paths64 solution = Clipper.Intersect(subj, clip, FillRule.NonZero);

      //Delphi
      var 
        subject, clip, solution: TPaths64;
      begin
        SetLength(subject, 1);
        subject[0] := MakePath([100, 50, 10, 79, 65, 2, 65, 98, 10, 21]);
        SetLength(clip, 1);
        clip[0] := MakePath([98, 63, 4, 68, 77, 8, 52, 100, 19, 12]);
        solution := Intersect( subject, clip, frNonZero);