+MAKE_SCHEME_CALLBACK (Self_alignment_interface, avoid_x_colliding_grobs, 2);
+SCM
+Self_alignment_interface::avoid_x_colliding_grobs (SCM smob, SCM o)
+{
+ SCM avoided = avoid_colliding_grobs (unsmob_grob (smob), X_AXIS, robust_scm2double (o, 0.0));
+ return scm_is_null (avoided) ? o : avoided;
+}
+
+MAKE_SCHEME_CALLBACK (Self_alignment_interface, x_colliding_grobs, 1);
+SCM
+Self_alignment_interface::x_colliding_grobs (SCM smob)
+{
+ Grob *me = unsmob_grob (smob);
+ extract_grob_set (me, "potential-X-colliding-grobs", pot);
+ vector<Grob *> act;
+ Direction d = get_grob_direction (me->get_parent (Y_AXIS));
+ for (vsize i = 0; i < pot.size (); i++)
+ if (d == get_grob_direction (pot[i])
+ && to_boolean (pot[i]->get_property ("cross-staff")))
+ act.push_back (pot[i]);
+
+ SCM grobs_scm = Grob_array::make_array ();
+ unsmob_grob_array (grobs_scm)->set_array (act);
+
+ return grobs_scm;
+}
+
+SCM
+Self_alignment_interface::avoid_colliding_grobs (Grob *me, Axis a, Real offset)
+{
+ extract_grob_set (me, a == X_AXIS ? "X-colliding-grobs" : "Y-colliding-grobs", colls);
+ if (!colls.size ())
+ return SCM_EOL;
+ vector<Interval> ivs;
+
+ Item *refp = dynamic_cast<Item *> (common_refpoint_of_array (colls, me, a));
+ if (!refp)
+ return SCM_EOL;
+
+ Interval iv = me->extent (me, a) + offset;
+ for (vsize i = 0; i < colls.size (); i++)
+ ivs.push_back (colls[i]->extent (refp, a));
+
+ Interval_minefield minefield (Interval (iv.center (), iv.center ()), iv.length ());
+ for (vsize i = 0; i < ivs.size (); i++)
+ minefield.add_forbidden_interval (ivs[i]);
+ minefield.solve ();
+ Interval pos = minefield.feasible_placements ();
+
+ if (pos[LEFT] == pos[RIGHT])
+ return SCM_EOL;
+
+ Direction col_dir = ((abs (pos[LEFT] - iv.center ())
+ + robust_scm2double (me->get_property ("collision-bias"), 0.0))
+ > abs (pos[RIGHT] - iv.center ()))
+ ? RIGHT
+ : LEFT;
+
+ return scm_from_double ((pos[col_dir] - (iv.length () / 2)
+ + col_dir
+ * robust_scm2double (me->get_property ("collision-padding"), 0.0)));
+}
+