Follow MIDI control values with automation faders.

Fixes bug #6166 (except record).

This attempts to follow the "current" control value somewhat aggressively:

* On locate, slider is set to the value from the top region at the new
  transport position.

* Playback or MIDI input is followed "live".

* Whenever the slider is moved (including automatically), that value is emitted
  as an immediate event to keep external gear in sync.

General idea is that the Ardour slider should act as a mirror of an external
hardware knob, and both should be synced to whatever the control is at the
current transport position.  Since we lack real playback/touch/etc modes for
these for now, we must choose one behaviour, and this seems like the most
reasonable one.

Follow is handled in the audio thread, which is probably not ideal, but since
these controls have no lists and do not record, should be fine.  Probably.

libs/ardour/ardour/midi_track.h

@@ -47,6 +47,7 @@ public:
 
 	void realtime_handle_transport_stopped ();
 	void realtime_locate ();
+	void non_realtime_locate (framepos_t);
 
 	boost::shared_ptr<Diskstream> create_diskstream ();
 	void set_diskstream (boost::shared_ptr<Diskstream>);
@@ -183,6 +184,9 @@ private:
 	void track_input_active (IOChange, void*);
 	void map_input_active (bool);
 
+	/** Update automation controls to reflect any changes in buffers. */
+	void update_controls (const BufferSet& bufs);
+
 	void filter_channels (BufferSet& bufs, ChannelMode mode, uint32_t mask); 
 
 /* if mode is ForceChannel, force mask to the lowest set channel or 1 if no

libs/ardour/ardour/parameter_types.h

@@ -24,6 +24,7 @@
 #include <stdint.h>
 
 #include "ardour/types.h"
+#include "evoral/Parameter.hpp"
 #include "evoral/midi_events.h"
 
 namespace ARDOUR {
@@ -54,6 +55,26 @@ midi_parameter_type(uint8_t status)
 	}
 }
 
+inline Evoral::Parameter
+midi_parameter(const uint8_t* buf, const uint32_t len)
+{
+	const uint8_t channel = buf[0] & 0x0F;
+	switch (midi_parameter_type(buf[0])) {
+	case MidiCCAutomation:
+		return Evoral::Parameter(MidiCCAutomation, channel, buf[1]);
+	case MidiPgmChangeAutomation:
+		return Evoral::Parameter(MidiPgmChangeAutomation, channel);
+	case MidiChannelPressureAutomation:
+		return Evoral::Parameter(MidiChannelPressureAutomation, channel);
+	case MidiPitchBenderAutomation:
+		return Evoral::Parameter(MidiPitchBenderAutomation, channel);
+	case MidiSystemExclusiveAutomation:
+		return Evoral::Parameter(MidiSystemExclusiveAutomation, channel);
+	default:
+		return Evoral::Parameter(NullAutomation);
+	}
+}
+
 inline bool
 parameter_is_midi(AutomationType type)
 {

libs/ardour/midi_track.cc

@@ -34,6 +34,7 @@
 #include "pbd/convert.h"
 #include "evoral/midi_util.h"
 
+#include "ardour/beats_frames_converter.h"
 #include "ardour/buffer_set.h"
 #include "ardour/debug.h"
 #include "ardour/delivery.h"
@@ -42,6 +43,7 @@
 #include "ardour/midi_diskstream.h"
 #include "ardour/midi_playlist.h"
 #include "ardour/midi_port.h"
+#include "ardour/midi_region.h"
 #include "ardour/midi_track.h"
 #include "ardour/parameter_types.h"
 #include "ardour/port.h"
@@ -318,6 +320,20 @@ MidiTrack::set_state_part_two ()
 	return;
 }
 
+void
+MidiTrack::update_controls(const BufferSet& bufs)
+{
+	const MidiBuffer& buf = bufs.get_midi(0);
+	for (MidiBuffer::const_iterator e = buf.begin(); e != buf.end(); ++e) {
+		const Evoral::MIDIEvent<framepos_t>&     ev      = *e;
+		const Evoral::Parameter                  param   = midi_parameter(ev.buffer(), ev.size());
+		const boost::shared_ptr<Evoral::Control> control = this->control(param);
+		if (control) {
+			control->set_double(ev.value(), _session.transport_frame(), false);
+		}
+	}
+}
+
 /** @param need_butler to be set to true if this track now needs the butler, otherwise it can be left alone
  *  or set to false.
  */
@@ -470,6 +486,42 @@ MidiTrack::realtime_handle_transport_stopped ()
 	}
 }
 
+void
+MidiTrack::non_realtime_locate (framepos_t pos)
+{
+	Track::non_realtime_locate(pos);
+
+	boost::shared_ptr<MidiPlaylist> playlist = midi_diskstream()->midi_playlist();
+	if (!playlist) {
+		return;
+	}
+
+	/* Get the top unmuted region at this position. */
+	boost::shared_ptr<MidiRegion> region = boost::dynamic_pointer_cast<MidiRegion>(
+		playlist->top_unmuted_region_at(pos));
+	if (!region) {
+		return;
+	}
+
+	Glib::Threads::Mutex::Lock lm (_control_lock, Glib::Threads::TRY_LOCK);
+	if (!lm.locked()) {
+		return;
+	}
+
+	/* Update track controllers based on its "automation". */
+	const framepos_t     origin = region->position() - region->start();
+	BeatsFramesConverter bfc(_session.tempo_map(), origin);
+	for (Controls::const_iterator c = _controls.begin(); c != _controls.end(); ++c) {
+		boost::shared_ptr<MidiTrack::MidiControl> tcontrol;
+		boost::shared_ptr<Evoral::Control>        rcontrol;
+		if ((tcontrol = boost::dynamic_pointer_cast<MidiTrack::MidiControl>(c->second)) &&
+		    (rcontrol = region->control(tcontrol->parameter()))) {
+			const Evoral::Beats pos_beats = bfc.from(pos - origin);
+			tcontrol->set_value(rcontrol->list()->eval(pos_beats.to_double()));
+		}
+	}
+}
+
 void
 MidiTrack::push_midi_input_to_step_edit_ringbuffer (framecnt_t nframes)
 {
@@ -539,6 +591,8 @@ MidiTrack::write_out_of_band_data (BufferSet& bufs, framepos_t /*start*/, framep
 {
 	MidiBuffer& buf (bufs.get_midi (0));
 
+	update_controls (bufs);
+
 	// Append immediate events
 
 	if (_immediate_events.read_space()) {

libs/evoral/evoral/MIDIEvent.hpp

@@ -104,6 +104,21 @@ public:
 		return this->size() == 10    && this->_buf[0] == 0xf0 && this->_buf[1] == 0x7f && 
 		       this->_buf[3] == 0x01 && this->_buf[4] == 0x01;
 	}
+
+	inline uint16_t value() const {
+		switch (type()) {
+		case MIDI_CMD_CONTROL:
+			return cc_value();
+		case MIDI_CMD_BENDER:
+			return pitch_bender_value();
+		case MIDI_CMD_NOTE_PRESSURE:
+			return aftertouch();
+		case MIDI_CMD_CHANNEL_PRESSURE:
+			return channel_pressure();
+		default:
+			return 0;
+		}
+	}
 };
 
 } // namespace Evoral