triggerbox: add MIDITrigger channel mapping

libs/ardour/ardour/triggerbox.h

@@ -501,6 +501,11 @@ class LIBARDOUR_API MIDITrigger : public Trigger {
 	void unset_all_patch_changes ();
 	bool patch_change_set (uint8_t channel) const;
 
+	void set_channel_map (int channel, int target);
+	void unset_channel_map (int channel);
+	int channel_map (int channel);
+	std::vector<int> const & channel_map() const { return _channel_map; }
+
   protected:
 	void retrigger ();
 
@@ -520,6 +525,7 @@ class LIBARDOUR_API MIDITrigger : public Trigger {
 	boost::shared_ptr<MidiModel> model;
 
 	Evoral::PatchChange<MidiBuffer::TimeType> _patch_change[16];
+	std::vector<int> _channel_map;
 
 	int load_data (boost::shared_ptr<MidiRegion>);
 	void compute_and_set_length ();

libs/ardour/triggerbox.cc

@@ -1706,12 +1706,44 @@ MIDITrigger::MIDITrigger (uint32_t n, TriggerBox& b)
 {
 	Evoral::PatchChange<MidiBuffer::TimeType> pc (0, 0, 12, 0);
 	set_patch_change (pc);
+
+	_channel_map.assign (16, -1);
 }
 
 MIDITrigger::~MIDITrigger ()
 {
 }
 
+void
+MIDITrigger::set_channel_map (int channel, int target)
+{
+	if (channel < 0 || channel >= 16) {
+		return;
+	}
+	if (target < 0 || target >= 16) {
+		return;
+	}
+	_channel_map[channel] = target;
+}
+
+void
+MIDITrigger::unset_channel_map (int channel)
+{
+	if (channel < 0 || channel >= 16) {
+		return;
+	}
+	_channel_map[channel] = -1;
+}
+
+int
+MIDITrigger::channel_map (int channel)
+{
+	if (channel < 0 || channel >= 16) {
+		return -1;
+	}
+	return _channel_map[channel];
+}
+
 void
 MIDITrigger::set_patch_change (Evoral::PatchChange<MidiBuffer::TimeType> const & pc)
 {
@@ -2124,6 +2156,10 @@ MIDITrigger::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_sam
 			ev.scale_velocity (_gain);
 		}
 
+		if (_channel_map[ev.channel()] > 0) {
+			ev.set_channel (_channel_map[ev.channel()]);
+		}
+
 		if (ev.is_pgm_change() || (ev.is_cc() && ((ev.cc_number() == MIDI_CTL_LSB_BANK) || (ev.cc_number() == MIDI_CTL_MSB_BANK)))) {
 			if (_patch_change[ev.channel()].is_set()) {
 				/* skip pgm change info in data because trigger has its own */