VTK/Examples/Python/Visualization/HardwareSelector

import vtk
import vtk.util.numpy_support as VN
 
# Callback for when selection is changed
def selectionCallback(caller,eventId):
       hsel = vtk.vtkHardwareSelector()
       hsel.SetFieldAssociation(vtk.vtkDataObject.FIELD_ASSOCIATION_CELLS)
       hsel.SetRenderer(ren1)
 
       x,y = caller.GetRenderWindow().GetSize()
 
       # Create a small area around clicked point for selector area
       hsel.SetArea(0,0,x,y)
       res = hsel.Select()
 
       numNodes = res.GetNumberOfNodes()
       if (numNodes < 1):
               print "No visible cells"
       else:
               sel_node = res.GetNode(0)
               print 'Visible cell IDs: ', VN.vtk_to_numpy(sel_node.GetSelectionList()).tolist()
 
 
sphere = vtk.vtkSphereSource()
sphere.SetCenter( 0, 0, 0 )
sphere.SetRadius( 5.0 )
 
sphereMapper = vtk.vtkPolyDataMapper()
sphereMapper.SetInputConnection(sphere.GetOutputPort())
 
sphereActor = vtk.vtkActor()
sphereActor.SetMapper(sphereMapper)
 
ren1 = vtk.vtkRenderer()
ren1.AddActor(sphereActor)
ren1.SetBackground(0.1, 0.2, 0.4)
ren1.GetActiveCamera().ParallelProjectionOn()
 
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren1)
renWin.SetSize(300, 300)
 
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)
iren.AddObserver("UserEvent", selectionCallback)
 
style = vtk.vtkInteractorStyleTrackballCamera()
iren.SetInteractorStyle(style)
renWin.GetInteractor().SetInteractorStyle(style)
 
ren1.ResetCamera()
renWin.Render()
 
iren.Initialize()
iren.Start()