Function ncollide3d::query::closest_points_internal::ball_against_ball

pub fn ball_against_ball<N: RealField>(
    center1: &Point<N>, 
    b1: &Ball<N>, 
    center2: &Point<N>, 
    b2: &Ball<N>, 
    margin: N
) -> ClosestPoints<N>

Proximity between balls.