C# clip linesegment with clipper library

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独厮守ぢ
独厮守ぢ 2021-01-19 07:09

I am using clipper for performing a bunch of operations on polygons which represent the outlines of objects in my program. The thing is, I now want to clip a grid of line se

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  • 2021-01-19 08:03

    Using Clipper ver 6 ...

    using ClipperLib;
    
    using Path = List<IntPoint>;
    using Paths = List<List<IntPoint>>;
    
    static Polygon IntsToPolygon(Int64[] ints)
    {
      int len1 = ints.Length / 2;
      Polygon result = new Polygon(len1);
      for (int i = 0; i < len1; i++)
        result.Add(new IntPoint(ints[i * 2], ints[i * 2 + 1]));
      return result;
    }
    
    
    static void Main(string[] args)
    {
        Paths clip = new Paths(); //clipping polygon(s)
        //make a polygon in the shape of a pentagram
        //with center (200,200) and radius 100 ...
        Int64[][] ints1 = new Int64[][] 
        {
        new Int64[]{222, 169, 295, 169, 236, 212, 259, 281, 200, 238, 
          141, 281, 164, 212, 105, 169, 178, 169, 200, 100}
        };
        clip.Add(IntsToPolygon(ints1[0]));
    
        Paths subj = new Paths(); //subject paths, could be open or closed here
        int gridWidth = 5;
        int loopCnt = 200 / gridWidth;
    
        //now make grid lines and add them to subj ready for clipping ...
    
        //add horizontal grid lines ...
        for (int i = 0; i <= loopCnt; i++)
        {
        Path gridLine = new Path(2);
        gridLine.Add(new IntPoint(100, 100 + i * gridWidth));
        gridLine.Add(new IntPoint(300, 100 + i * gridWidth));
        subj.Add(gridLine);
        }
        //add vertical grid lines ...
        for (int i = 0; i <= loopCnt; i++)
        {
        Path gridLine = new Path(2);
        gridLine.Add(new IntPoint(100 + i * gridWidth, 100));
        gridLine.Add(new IntPoint(100 + i * gridWidth, 300));
        subj.Add(gridLine);
        }
    
        //now clip the gridlines (subj) with the pentagram (clip) ...
        Clipper c = new Clipper();
        PolyTree solution = new PolyTree();
        c.AddPaths(subj, PolyType.ptSubject, false); //ie paths NOT closed
        c.AddPaths(clip, PolyType.ptClip, true); //nb: clip paths MUST be closed
        c.Execute(ClipType.ctIntersection, 
          solution, PolyFillType.pftEvenOdd, PolyFillType.pftEvenOdd);
        Paths clippedGrids = Clipper.PolyTreeToPaths(solution);
    
        //Display the result (sorry, make your own display function) ...
        //Display(Paths p, Color stroke, Color brush, PolyFillType pft, bool IsClosed) 
        Display(subj, Color.FromArgb(0x18, 0, 0, 0x9c), 
            Color.Blue, PolyFillType.NonZero, false); //unclipped grid
        Display(clippedGrids, FromArgb(0, 0, 0, 0), 
            Color.Red, false); //clipped grid 
    
    }
    

    enter image description here

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