MAINT: Drop support for PySurfer + mayavi?

[larsoner]

Now that:

1. Brain / PyVista / PyVistaQt has begun to mature;
2. PyVista backend has good notebook support;
3. mayavi has gone even more unmaintained than usual (I have had a PR open for 3 months that fixes some bugs on latest vtk that hasn't been reviewed yet); and
4. PySurfer isn't too actively developed anymore

I propose that it's time that we drop support for it, as it lowers our maintenance burden: deprecate for 0.24, and in 0.25 remove the mayavi backend. We can leave the set_3d_backend infrastructure in place for future compatibility in case we want to migrate to a different 3D backend in the (probably distant) future.

I figured I'd ping @GuillaumeFavelier and @agramfort first since you've primarily been guiding the PyVista efforts. If you're on board, I'll ping the rest of the MNE steering committee since I think this is a potentially large enough change to warrant bothering everyone.

[agramfort]

yes +1 but I'd like to kill this bird with the new coreg GUI so we're done for good.

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[larsoner]

Oh right I forgot that the coreg GUI needed it.

I think there is actually another GUI -- mne kit2fiff. I have never used it, and I don't know how widely used it is...

[agramfort]

no idea if mne kit2fiff is actually still used?

maybe @teonbrooks or @christianbrodbeck knows?

[christianbrodbeck]

I am not aware of a replacement for the kit2fiff GUI, but since it only concerns a small subset of users maybe it could be kept as an special dependency, i.e. install mayavi if you want to use it?

[teonbrooks]

for kit2fiff the conversion can be done programmatically without the GUI and we now have other tools such as dig_montage, its corresponding viz, and coreg to do inspection. It was a useful module to ensure that the markers were placed in the correct locations and that the corresponding files (headshape points, head coil points) were properly processed. I think making note of when it is last supported and point to the tutorial on using dig_montage would be what's needed.

[agramfort]

I like this idea. Do you some basic script that would allow to replicate the GUI feature?

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[hoechenberger]

+1000 on dropping Mayavi

[teonbrooks]

I like this idea. Do you some basic script that would allow to replicate the GUI feature?

i can try to tackle this on Friday

[teonbrooks]

sorry, just had a time to come back to this. do we have access to the test data in an example script since this would require loading sqd/con files

[larsoner]

mne/GUI/tests should have tests for the functionality we want to replace, presumably those use sqd/con

[larsoner]

https://github.com/mne-tools/mne-python/blob/main/mne/gui/tests/test_kit2fiff_gui.py#L17

[teonbrooks]

i should clarify, for the example, instead of using the sample data, could i direct it to the mne/io/kit/tests/data if I want to show how to load kit data and construct a dig_montage for the kit2fiff equivalence

[larsoner]

Ahh, that doesn't come with pip installs, so you could buy it's better if we can find something else. You can use things in mne-testing-data if there's something in there that would work