/// set a minimum distance
static void add_rod (Grob*me, Grob * to, Real distance);
static void add_spring (Grob*me,Grob * to, Real dist, Real strength, bool);
/// set a minimum distance
static void add_rod (Grob*me, Grob * to, Real distance);
static void add_spring (Grob*me,Grob * to, Real dist, Real strength, bool);