+
+
+/*
+ [TODO]
+
+ handle rest under beam (do_post: beams are calculated now)
+ what about combination of collisions and rest under beam.
+
+ Should lookup
+
+ rest -> stem -> beam -> interpolate_y_position ()
+*/
+MAKE_SCHEME_CALLBACK (Beam, rest_collision_callback, 2);
+SCM
+Beam::rest_collision_callback (SCM element_smob, SCM axis)
+{
+ Grob *rest = unsmob_grob (element_smob);
+ Axis a = (Axis) gh_scm2int (axis);
+
+ assert (a == Y_AXIS);
+
+ Grob *st = unsmob_grob (rest->get_grob_property ("stem"));
+ Grob *stem = st;
+ if (!stem)
+ return gh_double2scm (0.0);
+ Grob *beam = unsmob_grob (stem->get_grob_property ("beam"));
+ if (!beam
+ || !Beam::has_interface (beam)
+ || !Beam::visible_stem_count (beam))
+ return gh_double2scm (0.0);
+
+ // make callback for rest from this.
+ // todo: make sure this calced already.
+
+ // Interval pos = ly_scm2interval (beam->get_grob_property ("positions"));
+ Interval pos (0, 0);
+ SCM s = beam->get_grob_property ("positions");
+ if (gh_pair_p (s) && gh_number_p (ly_car (s)))
+ pos = ly_scm2interval (s);
+
+ Real dy = pos.delta ();
+ // ugh -> use commonx
+ Real x0 = first_visible_stem (beam)->relative_coordinate (0, X_AXIS);
+ Real dx = last_visible_stem (beam)->relative_coordinate (0, X_AXIS) - x0;
+ Real dydx = dy && dx ? dy/dx : 0;
+
+ Direction d = Stem::get_direction (stem);
+ Real beamy = (stem->relative_coordinate (0, X_AXIS) - x0) * dydx + pos[LEFT];
+
+ Real staff_space = Staff_symbol_referencer::staff_space (rest);
+
+
+ Real rest_dim = rest->extent (rest, Y_AXIS)[d]*2.0 / staff_space; // refp??
+
+ Real minimum_dist
+ = gh_scm2double (rest->get_grob_property ("minimum-beam-collision-distance"));
+ Real dist =
+ minimum_dist + -d * (beamy - rest_dim) >? 0;
+
+ int stafflines = Staff_symbol_referencer::line_count (rest);
+
+ // move discretely by half spaces.
+ int discrete_dist = int (ceil (dist));
+
+ // move by whole spaces inside the staff.
+ if (discrete_dist < stafflines+1)
+ discrete_dist = int (ceil (discrete_dist / 2.0)* 2.0);
+
+ return gh_double2scm (-d * discrete_dist);
+}
+
+
+bool
+Beam::has_interface (Grob *me)
+{
+ return me->has_interface (ly_symbol2scm ("beam-interface"));
+}
+
+
+ADD_INTERFACE (Beam, "beam-interface",
+ "A beam.
+
+#'thickness= weight of beams, in staffspace
+
+
+We take the least squares line through the ideal-length stems, and
+then damp that using
+
+ damped = tanh (slope)
+
+this gives an unquantized left and right position for the beam end.
+Then we take all combinations of quantings near these left and right
+positions, and give them a score (according to how close they are to
+the ideal slope, how close the result is to the ideal stems, etc.). We
+take the best scoring combination.
+
+",
+ "concaveness-threshold dir-function quant-score auto-knee-gap gap chord-tremolo beamed-stem-shorten shorten least-squares-dy direction damping flag-width-function neutral-direction positions thickness");
+