using this, it works very fine, filling the matrix at the end with values like:
(0., 0., distance)
the cell index being the considered objects.
finally, it was the first gen stuff dtr adviced me.
maybe I could remove the sqrt() to improve things but … I have to say it works quite nice.
indeed, that distance calculation costs, but it provides a way to disable all OB3D too far from the camera, and it saves a lot of cpu..