fix linked midi-regions on different tracks #6541

A somewhat hacky solution to address missing note-off events when a
linked midi-region is used on separate tracks at the same time.
see the source-code comment for further info.

diff --git a/libs/ardour/midi_source.cc b/libs/ardour/midi_source.cc
index ab972fabd872222b329ae762aa92044b1dc168b1..0c18681dd4a7bbdac1008f753dbc9f52d8029259 100644 (file)
--- a/libs/ardour/midi_source.cc
+++ b/libs/ardour/midi_source.cc
@@ -205,6 +205,7 @@ MidiSource::midi_read (const Lock&                        lm,
                Evoral::Sequence<Evoral::Beats>::const_iterator& i = _model_iter;
                const bool linear_read = _last_read_end != 0 && start == _last_read_end;
                if (!linear_read || !_model_iter_valid) {
+#if 0
                        // Cached iterator is invalid, search for the first event past start
                        i = _model->begin(converter.from(start), false, filtered,
                                          linear_read ? &_model->active_notes() : NULL);
@@ -212,6 +213,43 @@ MidiSource::midi_read (const Lock&                        lm,
                        if (!linear_read) {
                                _model->active_notes().clear();
                        }
+#else
+                       /* hot-fix http://tracker.ardour.org/view.php?id=6541
+                        * "parallel playback of linked midi regions -> no note-offs"
+                        *
+                        * A midi source can be used by multiple tracks simultaneously,
+                        * in which case midi_read() can called from different tracks for
+                        * overlapping time-ranges.
+                        *
+                        * However there is only a single iterator for a given midi-source.
+                        * this results in every midi_read() performing a seek.
+                        *
+                        * if seeking is performed with
+                        *    _model->begin(converter.from(start),...)
+                        * the model is used for seeking. That method seeks to the first
+                        * *note-on* event after 'start'.
+                        *
+                        * _model->begin(conveter.from(  ) ,..) eventually calls
+                        * Sequence<Time>::const_iterator() in libs/evoral/src/Sequence.cpp
+                        * which looks up the note-event via seq.note_lower_bound(t);
+                        * but the sequence 'seq' only contains note-on events(!).
+                        * note-off events are implicit in Sequence<Time>::operator++()
+                        * via _active_notes.pop(); and not part of seq.
+                        *
+                        * see also http://tracker.ardour.org/view.php?id=6287#c16671
+                        * and call 1-900-ardour-midi ($4.99/min)
+                        *
+                        * The linear search below assures that reading starts at the first
+                        * event for the given time, regardless of its event-type.
+                        */
+                       for (i = _model->begin(); i != _model->end(); ++i) {
+                               const framecnt_t time_frames = converter.to(i->time());
+                               if (time_frames >= start) {
+                                       break;
+                               }
+                       }
+                       _model_iter_valid = true;
+#endif
                }
 
                _last_read_end = start + cnt;