wpf Viewport3d.GeometryModel3D.LinesCollec

Hi, if you want see line you must create triangles. Try following code:

  <Window.DataContext>  
    <local:ViewModel/>  
  </Window.DataContext>  
  
  
    <Viewport3D>  
      <Viewport3D.Camera>  
        <PerspectiveCamera Position="-10,20,10" LookDirection="40,-40,-40" UpDirection="0,0,1"/>  
      </Viewport3D.Camera>  
      <ModelVisual3D Content="{Binding MGroup}"/>  
    </Viewport3D>  
  
  
  public class ViewModel  
Hi, if you want see line you must create triangles. try following code:  
  
  {  
    public Model3DGroup MGroup { get => GetData(); }  
  
    private ObservableCollection<Line> col = new ObservableCollection<Line>();  
  
    private Model3DGroup GetData()  
    {  
      // collection of lines  
      Point pt1 = new Point(0, 0);  
      Point pt2 = new Point(10, 0);  
      for (int i = 0; i < 10; i++) col.Add(new Line() { X1 = pt1.X, X2 = pt2.X, Y1 = pt1.Y + i, Y2 = pt2.Y + i });  
      // create ModelGroup  
      Model3DGroup gr = new Model3DGroup();  
      gr.Children.Add(new DirectionalLight(Colors.White, new Vector3D(-1, -1, -3)));  
      foreach (var item in col)  
      {  
        GeometryModel3D mod = AddLine(new Point3D(item.X1, item.Y1, 0), new Point3D(item.X2, item.Y2, 0));  
        gr.Children.Add(mod);  
      }  
      return gr;  
    }  
  
    private GeometryModel3D AddLine(Point3D startPoint, Point3D endPoint)  
    {  
      var material = new DiffuseMaterial(new SolidColorBrush(Colors.Red));  
      var mesh = new MeshGeometry3D();  
      mesh.Positions.Add(startPoint);  
      mesh.Positions.Add(endPoint);  
      mesh.Positions.Add(new Point3D(startPoint.X, startPoint.Y + .1, startPoint.Z));  
      mesh.Positions.Add(new Point3D(endPoint.X, endPoint.Y + .1, endPoint.Z));  
      mesh.TriangleIndices.Add(0);  
      mesh.TriangleIndices.Add(1);  
      mesh.TriangleIndices.Add(3);  
      mesh.TriangleIndices.Add(3);  
      mesh.TriangleIndices.Add(2);  
      mesh.TriangleIndices.Add(0);  
      return new GeometryModel3D(mesh, material);  
    }  
  }  
  
  public class MyViewPort  
  {  
    private Viewport3D _vPort;  
    public Viewport3D VPort  
    {  
      get => this._vPort;  
      set  
      {  
        if (this._vPort == null)  
        {  
          this._vPort = value;  
          this._vPort.MouseDown += _vPort_MouseDown;  
          this._vPort.MouseMove += _vPort_MouseMove;  
          this._vPort.MouseUp += _vPort_MouseUp;  
          this._vPort.Loaded += _vPort_Loaded;  
        }  
      }  
    }  
  
    private AxisAngleRotation3D rot = new AxisAngleRotation3D(new Vector3D(0, 2, 0), 0);  
    private void _vPort_Loaded(object sender, RoutedEventArgs e)  
    {  
      var mod = this._vPort.Children[0] as ModelVisual3D;  
      mod.Transform = new RotateTransform3D(rot);  
    }  
  
    private Point pt = new Point(double.NaN, double.NaN);  
    private void _vPort_MouseDown(object sender, MouseButtonEventArgs e) => pt = e.GetPosition(this._vPort);  
    private void _vPort_MouseMove(object sender, MouseEventArgs e)  
    {  
      if (!double.IsNaN(pt.X))  
      {  
        Point pt1 = e.GetPosition(this._vPort);  
        double ang = pt1.X - pt.X;  
        rot.Angle = ang;  
      }  
    }  
    private void _vPort_MouseUp(object sender, MouseButtonEventArgs e) => pt = new Point(double.NaN, double.NaN);  
  }