Setting custom interactor behavior with vtklocal.LocalView

[ng-daniel]

For my application, I wanted to use vtkInteractorStyleImage , but I wanted panning behavior to be on left mouse instead of middle mouse so users on laptops and trackpads can still use the application.

So far, I've created a custom Python subclass of vtkInteractorStyleImage following this example from the vtk examples site, and set that as the interactor style for my renderWindowInteractor.

However, though the application recognizes the parent class of my override class (ie. switching to trackball as a parent changes the behavior to trackball), it only uses the default behaviors of each mouse button rather than my custom overrides.

A simple, reproducible example involves a slight modification of the motorcycle example from the Trame VTK examples website.

I added this class:

class CustomInteractorStyle(vtk.vtkInteractorStyleImage):
    """
    My custom interactor override.

    Goal is to switch the panning behavior of vtkInteractorStyleImage
    from middle mouse press/release to the left mouse press/release.
    
    Middle mouse should then do nothing.
    """

    def __init__(self, parent=None):
        super().__init__()
        
        self.AddObserver('LeftButtonPressEvent', self.left_button_press_event)
        self.AddObserver('LeftButtonReleaseEvent', self.left_button_release_event)
        self.AddObserver('MiddleButtonPressEvent', self.middle_button_press_event)
        self.AddObserver('MiddleButtonReleaseEvent', self.middle_button_release_event)

    def left_button_press_event(self, obj, event):
        self.OnMiddleButtonDown()
        return

    def left_button_release_event(self, obj, event):
        self.OnMiddleButtonUp()
        return

    def middle_button_press_event(self, obj, event):
        return

    def middle_button_release_event(self, obj, event):
        return

and changed this line:
renderWindowInteractor.GetInteractorStyle().SetCurrentStyleToTrackballCamera()
to this:
renderWindowInteractor.interactor_style = CustomInteractorStyle()

Why won't the overrides apply? Could it be that the observer event names are different between the vtklocal and vtk widgets? All help is appreciated.

[jourdain]

The issue with vtklocal is that the style that drive the camera run in the browser via the wasm bundle which does not know about your server side override.

Thankfully we have a new camera style manipulator that has been merged into VTK/C++ a week ago (I think) which should also work in wasm. That will allow you to customize your style as you want on the server and have wasm properly interpret it on the client side.

[jspanchu]

This should be possible soon. With the new vtkCameraManipulator (will be released in 9.7.0), you should be able to do:

style = vtk.vtkInteractorStyleManipulator(interactor=interactor)
style.manipualtors.append(
  vtkTrackballPan(mouse_button=vtkCameraManipulator.MouseButtonType.Left,
  ))

Now, since you are interested in 'image' type of panning, i think a new manipulator (named vtkTrackballPan2D) for that should be added.

We also need to enable serialization for all the manipulator classes.

[jspanchu]

After thinking more, we also need to reconcile that the manipulators should be pluggable into other interactor styles as well. In your case, you're probably interested in these actions from vtkInteractorStyleImage:

• R Reset the Window/Level
• X Reset to a sagittal view
• Y Reset to a coronal view
• Z Reset to an axial view

[ng-daniel]

Ah ok, so when 9.7.0 releases, I'll be able to "build my own version" of the vtkInteractorStyleImage style, except with the vtkTrackballPan set to left mouse instead of middle mouse. Thanks, I'm looking forwards to 9.7.0!

[jspanchu]

Yeah, something like that. Thanks for sharing your use case. It helps structuring the way the styles and manipulators work.