fix endless messages about MIDI events being dropped.

track-owned MIDI port buffers (at the Ardour level) get ::flush_buffers() called twice, once by Delivery::flush_buffers() which is called
at the end of MidiTrack::rol() to push data out in graph order, and then finally as a last-chance effort in PortManager::cycle_end().

This should not cause a repeated attempt to write the same data, but it was. Fixed by marking the buffer empty once its data has
been flushed into a backend port buffer.

1 files changed, 15 insertions, 1 deletions

diff --git a/libs/ardour/midi_port.cc b/libs/ardour/midi_port.cc
index de2263fad6..ae168356b6 100644
--- a/libs/ardour/midi_port.cc
+++ b/libs/ardour/midi_port.cc
@@ -174,12 +174,21 @@ MidiPort::flush_buffers (pframes_t nframes)
 {
 	if (sends_output ()) {
 
-		void* port_buffer = port_engine.get_buffer (_port_handle, nframes);
+		void* port_buffer = 0;
 		
 		if (_resolve_required) {
+			port_buffer = port_engine.get_buffer (_port_handle, nframes);
 			/* resolve all notes at the start of the buffer */
 			resolve_notes (port_buffer, 0);
 			_resolve_required = false;
+		} 
+		
+		if (_buffer->empty()) {
+			return;
+		}
+
+		if (!port_buffer) {
+			port_buffer = port_engine.get_buffer (_port_handle, nframes);
 		}
 
 		for (MidiBuffer::iterator i = _buffer->begin(); i != _buffer->end(); ++i) {
@@ -201,6 +210,11 @@ MidiPort::flush_buffers (pframes_t nframes)
 				     << " + " << _port_buffer_offset << endl;
 			}
 		}
+
+		/* done.. the data has moved to the port buffer, mark it so 
+		 */
+
+		_buffer->clear ();
 	}
 }