+ grow_dir_ = CENTER;
+ min_volume_ = min_volume;
+ max_volume_ = max_volume;
+}
+
+void
+Audio_span_dynamic::add_absolute (Audio_dynamic *d)
+{
+ assert (d);
+ dynamics_.push_back (d);
+}
+
+Moment
+remap_grace_duration (Moment m)
+{
+ return Moment (m.main_part_ + Rational (9, 40) * m.grace_part_,
+ Rational (0));
+}
+
+Real
+moment_to_real (Moment m)
+{
+ return remap_grace_duration (m).main_part_.to_double ();
+}
+
+int
+moment_to_ticks (Moment m)
+{
+ return int (moment_to_real (m) * 384 * 4);
+}
+
+void
+Audio_span_dynamic::render ()
+{
+ if (dynamics_.size () <= 1)
+ return;
+
+ assert (dynamics_[0]->volume_ >= 0);
+
+ while (dynamics_.back ()->volume_ > 0
+ && dynamics_.size () > 1
+ && sign (dynamics_.back ()->volume_ - dynamics_[0]->volume_) != grow_dir_)
+ {
+ dynamics_.erase (dynamics_.end () - 1);
+ }
+
+ if (dynamics_.size () <= 1)
+ {
+ programming_error ("Impossible or ambiguous (de)crescendo in MIDI.");
+ return;
+ }
+
+ Real start_v = dynamics_[0]->volume_;
+ if (dynamics_.back ()->volume_ < 0)
+ {
+ // The dynamic spanner does not end with an explicit dynamic script
+ // event. Adjust the end volume by at most 1/4 of the available
+ // volume range in this case.
+ dynamics_.back ()->volume_ = max (min (start_v + grow_dir_ * (max_volume_ - min_volume_) * 0.25, max_volume_), min_volume_);
+ }
+
+ Real delta_v = dynamics_.back ()->volume_ - dynamics_[0]->volume_;
+
+ Moment start = dynamics_[0]->get_column ()->when ();
+
+ Real total_t = moment_to_real (dynamics_.back ()->get_column ()->when () - start);
+
+ for (vsize i = 1; i < dynamics_.size (); i++)
+ {
+ Moment dt_moment = dynamics_[i]->get_column ()->when ()
+ - start;
+
+ Real dt = moment_to_real (dt_moment);
+
+ Real v = start_v + delta_v * (dt / total_t);
+
+ dynamics_[i]->volume_ = v;
+ }