feat: add WebXR Helper widget

[munozco]

This adds a WebXR Helper widget to enable VtkView and VtkLocalView to be used for a WebXR session.
vue-vtk-js PR: Kitware/vue-vtk-js#9

The new VtkWebXRHelper class contains the XrSessionTypes enum that has the same values as XrSessionTypes in vtk.js.

Here's an example that uses the new VtkWebXRHelper widget in a TrameApp:

with vuetify3.VContainer(fluid=True, classes="pa-0 fill-height"):
  with vtk.VtkView() as view:
      self.xr_widget = vtk.VtkWebXRHelper(draw_controllers_ray=True, enterXR=self.ctrl.enterXR, exitXR=self.ctrl.exitXR)
      with vtk.VtkGeometryRepresentation():
          vtk.VtkAlgorithm(vtk_class="vtkConeSource")

# [...]

# start a HmdVR WebXR session
self.xr_widget.startXR(vtk.VtkWebXRHelper.XrSessionTypes.HmdVR)

# stop the session
self.xr_widget.stopXR()

[jourdain]

You need to update the version of vue-vtk-js in that PR

https://github.com/Kitware/trame-vtk/blob/master/.fetch_externals.sh

[finetjul]

I do not understand how it knows on which view the helper applies...

[munozco]

The helper has a vtkView (or a vtkLocalView) as its parent. It can get the corresponding ClientView (or LocalView) thanks to the Vue.js provide/inject mechanism. For instance, the vtkView Vue component is providing the ClientView object here