ENH: interactive volume viz followup/todos

I’m raising a new issue to keep track of things that need to be done but are not part of https://github.com/mne-tools/mne-python/pull/5329

• Allow plotting surface data in volume plotters using the cortical ribbon (see closed glass brain PR)
• Visualization of vector fields on top of functional maps (after @britta-wstnr implements the computation aspect)
• Ability to save an animation of the functional map
• Getting a max: temporal / spatial (globally or within x mm of mouse click) / spatiotemporal
• be able to use arrows to move in time like we have eg in mne_analyze (right arrow : move one sample forward, shift+right arrow move by 10ms and the reverse for left arrow)
• I think we should have an entry in the visualization section in http://martinos.org/mne/stable/documentation.html on source estimates. Basically showing every option to visualize source estimation results : on surface, on volume, dipoles.
• Add more divergent colormaps in _limits_to_control_points, with proper transparent=True support (set middle to fully transparent, fmin->fmid linear from 0->1 as mne colormap already does) and nonlinear scaling of colormaps (which mne already does during its construction). (#5522)

cc @agramfort @sarangnemo

[larsoner]

@jasmainak marking this for the sprint in case you want to work on it

[larsoner]

I think most of this is YAGNI at this point and/or can be obtained from the 3D viz code so I’ll close. But let’s reopen if people are still enthusiastic about some of these features