# VisualizeDirectedGraph

VTKExamples/Python/Graphs/VisualizeDirectedGraph

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### Code

VisualizeDirectedGraph.py

    #!/usr/bin/env python
    import vtk

    def main():
        g = vtk.vtkMutableDirectedGraph()

        v1 = g.AddVertex()
        v2 = g.AddVertex()
        v3 = g.AddVertex()

        g.AddEdge ( v1, v2 )
        g.AddEdge ( v2, v3 )
        g.AddEdge ( v3, v1 )

        # Do layout manually before handing graph to the view.
        # This allows us to know the positions of edge arrows.
        graphLayoutView = vtk.vtkGraphLayoutView()

        layout = vtk.vtkGraphLayout()
        strategy = vtk.vtkSimple2DLayoutStrategy()
        layout.SetInputData(g)
        layout.SetLayoutStrategy(strategy)

        # Tell the view to use the vertex layout we provide
        graphLayoutView.SetLayoutStrategyToPassThrough()
        # The arrows will be positioned on a straight line between two
        # vertices so tell the view not to draw arcs for parallel edges
        graphLayoutView.SetEdgeLayoutStrategyToPassThrough()

        # Add the graph to the view. This will render vertices and edges,
        # but not edge arrows.
        graphLayoutView.AddRepresentationFromInputConnection(layout.GetOutputPort())

        # Manually create an actor containing the glyphed arrows.
        graphToPoly = vtk.vtkGraphToPolyData()
        graphToPoly.SetInputConnection(layout.GetOutputPort())
        graphToPoly.EdgeGlyphOutputOn()

        # Set the position (0: edge start, 1: edge end) where
        # the edge arrows should go.
        graphToPoly.SetEdgeGlyphPosition(0.98)

        # Make a simple edge arrow for glyphing.
        arrowSource = vtk.vtkGlyphSource2D()
        arrowSource.SetGlyphTypeToEdgeArrow()
        arrowSource.SetScale(0.1)
        arrowSource.Update()

        # Use Glyph3D to repeat the glyph on all edges.
        arrowGlyph = vtk.vtkGlyph3D()
        arrowGlyph.SetInputConnection(0, graphToPoly.GetOutputPort(1))
        arrowGlyph.SetInputConnection(1, arrowSource.GetOutputPort())

        # Add the edge arrow actor to the view.
        arrowMapper = vtk.vtkPolyDataMapper()
        arrowMapper.SetInputConnection(arrowGlyph.GetOutputPort())
        arrowActor = vtk.vtkActor()
        arrowActor.SetMapper(arrowMapper)
        graphLayoutView.GetRenderer().AddActor(arrowActor)

        graphLayoutView.ResetCamera()
        graphLayoutView.Render()
        graphLayoutView.GetInteractor().Start()

    if __name__ == '__main__':
        main()