From 8a06e6735d058cb132ef6f75df550353e2e0b70e Mon Sep 17 00:00:00 2001
From: Paul Davis <paul@linuxaudiosystems.com>
Date: Sun, 19 Jun 2016 23:41:26 -0400
Subject: [PATCH] add initial implementation of a "shadow port" for
 AsyncMIDIPort.

The shadow port is a secondary port that can be used to allow others to get a copy of part, all or none of the MIDI
stream received by the owner (input) port.
---
 libs/ardour/ardour/async_midi_port.h |  8 ++++-
 libs/ardour/async_midi_port.cc       | 50 ++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/libs/ardour/ardour/async_midi_port.h b/libs/ardour/ardour/async_midi_port.h
index 96a50ab198..931c404727 100644
--- a/libs/ardour/ardour/async_midi_port.h
+++ b/libs/ardour/ardour/async_midi_port.h
@@ -73,6 +73,9 @@ class LIBARDOUR_API AsyncMIDIPort : public ARDOUR::MidiPort, public MIDI::Port {
 	int selectable() const { return -1; }
 	void set_timer (boost::function<framecnt_t (void)>&);
 
+	void set_inbound_filter (boost::function<bool(MidiBuffer&,MidiBuffer&)>);
+	int add_shadow_port (std::string const &);
+
 	static void set_process_thread (pthread_t);
 	static pthread_t get_process_thread () { return _process_thread; }
 	static bool is_process_thread();
@@ -99,7 +102,10 @@ class LIBARDOUR_API AsyncMIDIPort : public ARDOUR::MidiPort, public MIDI::Port {
 	void make_connections ();
 	void init (std::string const &, Flags);
 
-    void flush_output_fifo (pframes_t);
+	void flush_output_fifo (pframes_t);
+
+	boost::shared_ptr<MidiPort> shadow_port;
+	boost::function<bool(MidiBuffer&,MidiBuffer&)> inbound_midi_filter;
 
 	static pthread_t _process_thread;
 };
diff --git a/libs/ardour/async_midi_port.cc b/libs/ardour/async_midi_port.cc
index bbcc0aab85..ff9a920c69 100644
--- a/libs/ardour/async_midi_port.cc
+++ b/libs/ardour/async_midi_port.cc
@@ -41,6 +41,30 @@ pthread_t AsyncMIDIPort::_process_thread;
 
 #define port_engine AudioEngine::instance()->port_engine()
 
+static bool
+filter_relax (MidiBuffer& in, MidiBuffer& out)
+{
+	return false;
+}
+
+static bool
+filter_copy (MidiBuffer& in, MidiBuffer& out)
+{
+	out.copy (in);
+	return false;
+}
+
+static bool
+filter_notes_only (MidiBuffer& in, MidiBuffer& out)
+{
+	for (MidiBuffer::iterator b = in.begin(); b != in.end(); ++b) {
+		if ((*b).is_note_on() || (*b).is_note_off()) {
+			out.push_back (*b);
+		}
+	}
+	return false;
+}
+
 AsyncMIDIPort::AsyncMIDIPort (string const & name, PortFlags flags)
 	: MidiPort (name, flags)
 	, MIDI::Port (name, MIDI::Port::Flags (0))
@@ -50,6 +74,7 @@ AsyncMIDIPort::AsyncMIDIPort (string const & name, PortFlags flags)
 	, output_fifo (2048)
 	, input_fifo (1024)
 	, _xthread (true)
+	, inbound_midi_filter (boost::bind (filter_notes_only, _1, _2))
 {
 }
 
@@ -145,6 +170,12 @@ AsyncMIDIPort::cycle_start (MIDI::pframes_t nframes)
 		if (!mb.empty()) {
 			_xthread.wakeup ();
 		}
+
+		if (shadow_port) {
+			inbound_midi_filter (mb, shadow_port->get_midi_buffer (nframes));
+		} else {
+			inbound_midi_filter (mb, mb);
+		}
 	}
 }
 
@@ -341,3 +372,22 @@ AsyncMIDIPort::is_process_thread()
 	return pthread_equal (pthread_self(), _process_thread);
 }
 
+int
+AsyncMIDIPort::add_shadow_port (string const & name)
+{
+	if (!ARDOUR::Port::receives_input()) {
+		return -1;
+	}
+
+	if (shadow_port) {
+		return -2;
+	}
+
+	/* shadow port is not async. */
+
+	if (!(shadow_port = boost::dynamic_pointer_cast<MidiPort> (AudioEngine::instance()->register_output_port (DataType::MIDI, name, false)))) {
+		return -3;
+	}
+
+	return 0;
+}
-- 
2.30.2