ZCallback

This property is only exposed when the pre-processor directive USINGZ has been defined. If this is the case, an Int64 Z member will be included in the definitions of both the Point64 and PointD classes. (This Z member is for user defined data and has nothing to do with 3D clipping.)

While most vertices in clipping solutions will correspond to input (subject and clip) vertices, there will also be new vertices wherever these segments intersect. This callback facilitates assigning user-defined Z values at these intersections. To aid the user in determining appropriate Z values, the function receives the vertices at both ends of the intersecting segments (ie four vertices). Subject vertices will be listed before clip vertices in the callback's parameter list.

In the following examples, use the Z callback to flag intersections (Z = 1) and differentiate them from non-intersection vertices (default Z = 0).

C++ Example:

    using namespace Clipper2Lib;
    
    // option1 - static callback function
    void myZCBD(const PointD& e1bot, const PointD& e1top,
      const PointD& e2bot, const PointD& e2top, PointD& pt)
    {
      pt.z = 1;
    }

      
    // option2 - class member callback function
    class MyClass {
    public:
      
      // PointD callback - see TestingZ_Double()
      void myZCBD(const PointD& e1bot, const PointD& e1top,
        const PointD& e2bot, const PointD& e2top, PointD& pt)
      {
        pt.z = 1;
      }
    };

        
    int main()
    {
    
    PathsD subject, solution;
    subject.push_back(MakePathD(
      {100, 50, 10, 79, 65, 2, 65, 98, 10, 21}));

    MyClass mc;
    ClipperD c;
    c.AddSubject(subject);
    
    //option 1: static function assignment
    c.SetZCallback(myZCB);
    
    /*  
    // option 2: class member function assignment
    c.SetZCallback(
      std::bind(&MyClass::myZCBD, mc, std::placeholders::_1,
        std::placeholders::_2, std::placeholders::_3,
        std::placeholders::_4, std::placeholders::_5));
    */
    
    c.Execute(ClipType::Union, FillRule::NonZero, solution);

    // display result
    SvgWriter svg;
    SvgAddSubject(svg, subject, FillRule::NonZero);
    SvgAddSolution(svg, solution, FillRule::NonZero, true);
    // draw a red circle around any intersections
    for (const auto& sol_path : solution)
    {
      if (sol_path.empty()) continue;
      PathsD ellipses;
      const double r = 3.0;
      for (const PointD& pt : sol_path)
        if (pt.z) ellipses.push_back(
          Ellipse(RectD(pt.x - r, pt.y - r, pt.x + r, pt.y + r), 11));
      svg.AddPaths(ellipses, false, 
        FillRule::NonZero, 0x20FF0000, 0xFFFF0000, 1, false);
    }
    SvgSaveToFile(svg, "usingz_D.svg", 600, 600, 20);
    }

C# Example:

    using Clipper2Lib;

    public class Application
    {
      public class MyCallbacks
      {
        public void MyCallbackD(PointD bot1, PointD top1,
          PointD bot2, PointD top2, ref PointD intersectPt)
        {
          intersectPt.Z = 1;
        }
      }

      public static void Main()
      {
        PathsD solution = new PathsD();
        PathsD subject = new PathsD();
        subject.Add(Clipper.MakePathD(
          new int[] { 100, 50, 10, 79, 65, 2, 65, 98, 10, 21 }));

        ClipperD c = new ClipperD();
        MyCallbacks cb = new MyCallbacks();
        c.ZCallback = cb.MyCallbackD;
        c.AddSubject(subject);
        c.Execute(ClipType.Union, FillRule.NonZero, solution);

        SvgWriter svg= new SvgWriter();
        SvgUtils.AddSubject(svg, subject);
        SvgUtils.AddSolution(svg, solution, false);
        // draw a red circle around any intersections
        for (int i = 0; i < solution[0].Count; i++)
        {
          if (solution[0][i].Z == 1)
            svg.DrawCircle(solution[0][i].X, solution[0][i].Y, 
              4, 1, 0x20FF0000, 0xFFFF0000);
        }
        svg.SaveToFile("usingz.svg", 400, 400);
      }

ClipperD.ZCallback

See Also