MRG+1: Enable interactivity inside notebook for pyvista backend

[GuillaumeFavelier]

What does this implement/fix?

Add basic interactivity inside a jupyter notebook for the PyVista backend. Please note that panel is required to achieve this.

Additional information

We obtain the following:

And this is the code used in the notebook:

from mne.viz import set_3d_backend
set_3d_backend("pyvista")

import mne
from mne.datasets import sample
data_path = sample.data_path()
raw_fname = data_path + '/MEG/sample/sample_audvis_raw.fif'
subjects_dir = data_path + '/subjects'
subject = 'sample'
trans = data_path + '/MEG/sample/sample_audvis_raw-trans.fif'
info = mne.io.read_info(raw_fname)
mne.viz.plot_alignment(info, trans, subject=subject, dig=True,
                       meg=['helmet', 'sensors'], subjects_dir=subjects_dir,
                       surfaces=['head-dense'])

[lgtm-com]

This pull request introduces 1 alert when merging 57fd24a into 066f6b9 - view on LGTM.com

new alerts:

• 1 for Unused local variable

[codecov]

Codecov Report

Merging #6437 into master will decrease coverage by <.01%.
The diff coverage is 55.55%.

@@            Coverage Diff             @@
##           master    #6437      +/-   ##
==========================================
- Coverage   89.27%   89.26%   -0.01%     
==========================================
  Files         411      411              
  Lines       74518    74534      +16     
  Branches    12317    12319       +2     
==========================================
+ Hits        66526    66536      +10     
- Misses       5135     5139       +4     
- Partials     2857     2859       +2

[GuillaumeFavelier]

What do you think @larsoner , @agramfort ?

[larsoner]

Maybe this can be done more simply as return '__IPYTHON__' in globals()? Not sure if it's better or worse. But at the very least, I don't see why you would assign to py rather than just doing __IPYTHON__ directly (it seems to be what the ipython docs do in my minimal searches)

[GuillaumeFavelier]

Surprisingly, both '__IPYTHON__' in globals() and globals().get('__IPYTHON__', False) returns False inside a jupyter notebook in my testing.
I'll modify to use __IPYTHON__ directly, thank you.

[larsoner]

Otherwise LGTM (but I did not test it)

[agramfort]

your example above works great for me in the notebook with interaction.

+1 for MRG

[larsoner]

Thanks @GuillaumeFavelier !