Why does the light_manager of MlabSceneModel not get set?

Question

I am using Mayavi for a 3D visualization with TraitsUI. The scene is a trait of the type MlabSceneModel. I want to change the lighting and trying to access scene.light_manager in a function called on the activated event. However, scene.light_manager is always None.

Using mlab.figure() to creates a scene which has a light manager, but as I want the scene to be integrated in the UI and not in an additional window this is no option for me.

Answer 1

Good question which threw me for a loop at first.

Looking at the tvtk source, the light manager is added to the scene when the interactor is generated, which occurs after scene activation. Furthermore, the first thing I tried, which was to listen to 'scene:light_manager' doesn't work because the light manager is a Property trait that doesn't directly change. That said, if you listen to the object itself, which is referred to by the property, it will trigger a notification on creation. In other words, do this:

class Application(HasTraits):
  scene=Instance(MlabSceneModel,())

  ...

  @on_trait_change('scene:scene_editor:light_manager')
  def muck_with_the_lights(self):
    print self.scene.light_manager