Adding spatial constraints has took me a lot of my (low) brain power last night, but I think I’ve finally found an acceptable solution. I’ve thus updated the filter to make it sensible also to the region clicked by the user.
I’ve recorded a new video (see below), where the role of the spatial constraint is clearly visible (at least at the beginning of the process).
Let me know if that works for you !
Now, I have to think of a way to optimize the whole stuff, as it seems it’s a bit slow on computer with less than 8 cores 
Any feedback appreciated !