# VTK9 regression: vtkFollower unpickable

**URL:** <https://discourse.vtk.org/t/vtk9-regression-vtkfollower-unpickable/4991>\
**Category:** Development\
**Created:** [January 13, 2021, 12:05am UTC](https://discourse.vtk.org/t/vtk9-regression-vtkfollower-unpickable/4991 "2021-01-13T00:05:34Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![marcomusy](https://discourse.vtk.org/user_avatar/discourse.vtk.org/marcomusy/32/95_2.png) [@marcomusy](https://discourse.vtk.org/u/marcomusy)\
**Post date:** [January 13, 2021, 12:05am UTC](https://discourse.vtk.org/t/vtk9-regression-vtkfollower-unpickable/4991/1 "2021-01-13T00:05:34Z")

</div>

This works fine in vtk8 but fails in vtk9 for objects with opacity \< 1:

```python
import vtk

cone = vtk.vtkConeSource()

coneMapper = vtk.vtkPolyDataMapper()
coneMapper.SetInputConnection(cone.GetOutputPort())

coneActor = vtk.vtkFollower()
coneActor.SetMapper(coneMapper)
coneActor.GetProperty().SetOpacity(0.5) # BUG

ren = vtk.vtkRenderer()
ren.AddActor(coneActor)

renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)

iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)

def myCallback(iren, event_string):
    x, y = iren.GetEventPosition()
    picker = vtk.vtkPropPicker()
    picker.PickProp(x, y, ren)
    print('clicked', [picker.GetActor()])

iren.AddObserver("LeftButtonPressEvent", myCallback)
iren.Initialize()
iren.Start()

```

vtk8.1.2:

> clicked [(vtkmodules.vtkRenderingCore.vtkFollower)0x7fad9af27b40]

vtk9.0.1:

> clicked [None]

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<div class="post-metadata">

**Author:** ![lassoan](https://discourse.vtk.org/user_avatar/discourse.vtk.org/lassoan/32/50_2.png) [@lassoan](https://discourse.vtk.org/u/lassoan)\
**Post date:** [January 13, 2021, 1:26am UTC](https://discourse.vtk.org/t/vtk9-regression-vtkfollower-unpickable/4991/2 "2021-01-13T01:26:56Z")

</div>

I’ve tried this script in VTK 8.2 and VTK 9.0 and in both just got `clicked [None]`.

Adding `coneActor.ForceOpaqueOn()` fixes the issue.

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<div class="post-metadata">

**Author:** ![marcomusy](https://discourse.vtk.org/user_avatar/discourse.vtk.org/marcomusy/32/95_2.png) [@marcomusy](https://discourse.vtk.org/u/marcomusy)\
**Post date:** [January 13, 2021, 2:33am UTC](https://discourse.vtk.org/t/vtk9-regression-vtkfollower-unpickable/4991/3 "2021-01-13T02:33:05Z")

</div>

Thanks!