MRG: Link cameras in _LinkViewer

[GuillaumeFavelier]

This PR adds parameters to link_brains() to decide what to link: time controller and/or camera controls.

ToDo

• Fix camera update delay
• Update testing in test_3d.py
• Rename the time_viewer used as reference into leader
• Check stc time infos
• Link time course canvas

It's an item of #7162
Related to #7959

[agramfort]

@bloyl can you give it a try?

[bloyl]

Sorry for the delay in testing this.

This is pretty cool and does what I'd like.

A couple of things I noticed.

1. The camera doesn't force an update on the other renderer so things get laggy. I assume this is what you mean by Fix camera update delay in the description. but thought I'd mention it.
2. The time linking only works on the slider. if you click in the time course plot only the one brain updates.
3. You are currently allowed to time link brains that have different time axis. but since the linking is on time index this causes things to get out of sync.

My suggestion for point 3 would be use the actual time as opposed to the index to do the linking. Additionally I would add a time='auto' option as the default. this would use time=True if the linked brain objects all have the time array and false if they don't, supporting both linked multiple evoked STCs and unlinked stcs (say evoked and a PSD) with the default. Additonally if a user had evoked stcs with different time axis that were actually comparable (maybe historic data or something) they could force time=True to still have the linking.

[GuillaumeFavelier]

The camera doesn't force an update on the other renderer so things get laggy.

The cameras are linked but the event "the camera has been modified" is not captured simply because I don't know how to do that. And since #7517, the plotter is not updated automatically. I see 2 ways to fix this. Either capture the vtk event (interactor, camera...) or allow automatic update again.

The time linking only works on the slider

Nice catch! I'll take care of this :)

You are currently allowed to time link brains that have different time axis.

Hm, this is not intended... I have to check the time axes somehow. @larsoner, @agramfort any idea on how to deal with this?

[agramfort]

Hm, this is not intended... I have to check the time axes somehow. @larsoner, @agramfort any idea on how to deal with this?

stc.times should match between linked brains

[GuillaumeFavelier]

2. and 3) should be fixed by now. I'll investigate 1) and see if I can capture the right VTK event to update the plotters. Otherwise, I'll have to re-enable automatic update to mitigate.

[GuillaumeFavelier]

It turns out, the camera ModifiedEvent does the trick! I invite you to try it out @bloyl :)

Reference: http://vtk.1045678.n5.nabble.com/Vtk-Camera-Postion-Event-td5727757.html

[bloyl]

This second check throws ValueError: operands could not be broadcast if the brain_times are of different lengths and more than one.

why not only do the check if you have to (time == True)

        if time and not all(len(x) == len(brain_times[0]) for x in brain_times):
            time = False
        if time and not all(all(np.equal(x, brain_times[0])) for x in brain_times):
            time = False

to test just link a plot of an evoked stc with a cropped copy of the same stc

[bloyl]

Other than my comment above this is working for me.

Additional question, how did you make the 4 panel figure on the right?

[GuillaumeFavelier]

how did you make the 4 panel figure on the right?

I use the following parameters: hemi='split', views=['lat', 'med']

[GuillaumeFavelier]

Feel free to have a look or even test it @agramfort, @larsoner