SelectedVerticesAndEdgesObserver

#!/usr/bin/env python3

# noinspection PyUnresolvedReferences
import vtkmodules.vtkInteractionStyle
# noinspection PyUnresolvedReferences
import vtkmodules.vtkRenderingOpenGL2
from vtkmodules.vtkCommonColor import vtkNamedColors
from vtkmodules.vtkCommonDataModel import vtkSelectionNode
from vtkmodules.vtkInfovisCore import vtkRandomGraphSource
from vtkmodules.vtkViewsInfovis import vtkGraphLayoutView


def main():
    colors = vtkNamedColors()

    source = vtkRandomGraphSource()

    view = vtkGraphLayoutView()
    view.AddRepresentationFromInputConnection(source.output_port)

    rep = view.GetRepresentation(0)

    # The vtkRenderedGraphRepresentation should already have a vtkAnnotationLink,
    # so we just want to grab it and add an observer with our callback function
    # attached.
    link = rep.GetAnnotationLink()
    link.AddObserver('AnnotationChangedEvent', selection_callback)

    view.render_window.size = (600, 600)
    view.render_window.window_name = 'SelectedVerticesAndEdgesObserver'
    view.renderer.background = colors.GetColor3d('MidnightBlue')
    view.renderer.background2 = colors.GetColor3d('RoyalBlue')

    view.ResetCamera()
    view.Render()
    view.interactor.Start()


def selection_callback(caller, event):
    # Use the shift key to select both nodes and edges.
    # The nodes can either vertices or edges.
    sel = caller.current_selection
    vertices = vtkSelectionNode()
    edges = vtkSelectionNode()
    node0 = sel.GetNode(0)
    node0_field_type = node0.field_type
    if node0_field_type == vtkSelectionNode.VERTEX:
        vertices = node0
    elif node0_field_type == vtkSelectionNode.EDGE:
        edges = node0

    node1 = sel.GetNode(1)
    if node1:
        node1_field_type = node1.field_type
        if node1_field_type == vtkSelectionNode.VERTEX:
            vertices = node1
        elif node1_field_type == vtkSelectionNode.EDGE:
            edges = node1

    vertex_list = vertices.selection_list
    if vertex_list:
        print(f'There are {vertex_list.number_of_tuples} vertices selected.')
    has_vertices = vertex_list and vertex_list.number_of_tuples > 0
    if has_vertices:
        vertex_ids = list()
        for i in range(0, vertex_list.number_of_tuples):
            vertex_ids.append(vertex_list.GetValue(i))
        print(f'Vertex IDs: {", ".join(map(str, vertex_ids))}')

    edge_list = edges.selection_list
    if edge_list:
        print(f'There are {edge_list.number_of_tuples} edges selected.')
    has_edges = edge_list and edge_list.number_of_tuples > 0
    if has_edges:
        edge_ids = list()
        for i in range(0, edge_list.number_of_tuples):
            edge_ids.append(edge_list.GetValue(i))
        print(f'Edge IDs: {", ".join(map(str, edge_ids))}')

    if has_vertices or has_edges:
        print('- - -')
    else:
        print()


if __name__ == '__main__':
    main()