Add a dedicated export method to MidiRegion

To export a MIDI region to a file, the code used MidiRegion::clone()
since it takes care of creating a new file-backed source with the wanted
contents. Nevertheless, it had several side-effects:
- it created and registered a new region which is confusing to users
- it only exported notes that were in the region range, but didn't
  remove the region start offset from MIDI events, essentially producing
  a spurious silence at the beginning of the exported file (this is not
  a problem for region cloning because the newly created region is made
  aware of the offset and caters for it).

Add a dedicated code path for export, that uses the new offsetting
capabilities of MidiModel::write_section_to().

1 files changed, 13 insertions, 0 deletions

diff --git a/libs/ardour/ardour/midi_source.h b/libs/ardour/ardour/midi_source.h
index 7f2ddfbc22..c8b4263e2a 100644
--- a/libs/ardour/ardour/midi_source.h
+++ b/libs/ardour/ardour/midi_source.h
@@ -63,6 +63,19 @@ class LIBARDOUR_API MidiSource : virtual public Source, public boost::enable_sha
 	              Evoral::Beats                 begin = Evoral::MinBeats,
 	              Evoral::Beats                 end   = Evoral::MaxBeats);
 
+	/** Export the midi data in the given time range to another MidiSource
+	 * \param newsrc MidiSource to which data will be written. Should be a
+	 *        new, empty source. If it already has contents, the results are
+	 *        undefined. Source must be writable.
+	 * \param begin time of earliest event that can be written.
+	 * \param end time of latest event that can be written.
+	 * \return zero on success, non-zero if the write failed for any reason.
+	 */
+	int export_write_to (const Lock&                   lock,
+	                     boost::shared_ptr<MidiSource> newsrc,
+	                     Evoral::Beats                 begin,
+	                     Evoral::Beats                 end);
+
 	/** Read the data in a given time range from the MIDI source.
 	 * All time stamps in parameters are in audio frames (even if the source has tempo time).
 	 * \param dst Ring buffer where read events are written.