Implement Count-In (before recording), fixed BPM, up to 2 bars

libs/ardour/ardour/session.h

@@ -1898,6 +1898,7 @@ class LIBARDOUR_API Session : public PBD::StatefulDestructible, public PBD::Scop
 	void   click (framepos_t start, framecnt_t nframes);
 	void   run_click (framepos_t start, framecnt_t nframes);
 	void   add_click (framepos_t pos, bool emphasis);
+	framecnt_t _count_in_samples;
 
 	std::vector<Route*> master_outs;
 

libs/ardour/ardour/session_configuration_vars.h

@@ -36,6 +36,7 @@ CONFIG_VARIABLE (bool, auto_return, "auto-return", false)
 CONFIG_VARIABLE (bool, auto_input, "auto-input", true)
 CONFIG_VARIABLE (bool, punch_in, "punch-in", false)
 CONFIG_VARIABLE (bool, punch_out, "punch-out", false)
+CONFIG_VARIABLE (bool, count_in, "count-in", false)
 CONFIG_VARIABLE (MonitorChoice, session_monitoring, "session-monitoring", MonitorAuto)
 CONFIG_VARIABLE (bool, layered_record_mode, "layered-record-mode", false)
 CONFIG_VARIABLE (uint32_t, subframes_per_frame, "subframes-per-frame", 100)

libs/ardour/session.cc

@@ -300,6 +300,7 @@ Session::Session (AudioEngine &eng,
 	, click_length (0)
 	, click_emphasis_length (0)
 	, _clicks_cleared (0)
+	, _count_in_samples (0)
 	, _play_range (false)
 	, _range_selection (-1,-1)
 	, _object_selection (-1,-1)

libs/ardour/session_process.cc

@@ -314,6 +314,47 @@ Session::process_with_events (pframes_t nframes)
 		process_event (ev);
 	}
 
+	/* count in */
+	if (_transport_speed != 1.0 && _count_in_samples > 0) {
+		_count_in_samples = 0;
+	}
+
+	if (_count_in_samples > 0) {
+		framecnt_t ns = std::min ((framecnt_t)nframes, _count_in_samples);
+
+		no_roll (ns);
+		run_click (_transport_frame - _count_in_samples, ns);
+
+		_count_in_samples -= ns;
+		nframes -= ns;
+
+		/* process events.. */
+		if (!events.empty() && next_event != events.end()) {
+			SessionEvent* this_event = *next_event;
+			Events::iterator the_next_one = next_event;
+			++the_next_one;
+
+			while (this_event && this_event->action_frame == _transport_frame) {
+				process_event (this_event);
+				if (the_next_one == events.end()) {
+					this_event = 0;
+				} else {
+					this_event = *the_next_one;
+					++the_next_one;
+				}
+			}
+			set_next_event ();
+		}
+
+		check_declick_out ();
+
+		if (nframes == 0) {
+			return;
+		} else {
+			_engine.split_cycle (ns);
+		}
+	}
+
 	/* Decide on what to do with quarter-frame MTC during this cycle */
 
 	bool const was_sending_qf_mtc = _send_qf_mtc;

libs/ardour/session_transport.cc

@@ -45,6 +45,7 @@
 #include "ardour/scene_changer.h"
 #include "ardour/session.h"
 #include "ardour/slave.h"
+#include "ardour/tempo.h"
 #include "ardour/operations.h"
 
 #include "pbd/i18n.h"
@@ -1616,6 +1617,38 @@ Session::start_transport ()
 		if (!dynamic_cast<MTC_Slave*>(_slave)) {
 			send_immediate_mmc (MIDI::MachineControlCommand (MIDI::MachineControl::cmdDeferredPlay));
 		}
+
+		if (actively_recording() && click_data && config.get_count_in ()) {
+			/* calculate count-in duration (in audio samples)
+			 * - use [fixed] tempo/meter at _transport_frame
+			 * - calc duration of 1 bar + time-to-beat before or at transport_frame
+			 */
+			const Tempo& tempo = _tempo_map->tempo_at_frame (_transport_frame);
+			const Meter& meter = _tempo_map->meter_at_frame (_transport_frame);
+
+			double div = meter.divisions_per_bar ();
+			double pulses = _tempo_map->exact_qn_at_frame (_transport_frame, 0) * div / 4.0;
+			double beats_left = fmod (pulses, div);
+
+			_count_in_samples = meter.frames_per_bar (tempo, _current_frame_rate);
+
+			double dt = _count_in_samples / div;
+			if (beats_left == 0) {
+				/* at bar boundary, count-in 2 bars before start. */
+				_count_in_samples *= 2;
+			} else {
+				/* beats left after full bar until roll position */
+				_count_in_samples += meter.frames_per_grid (tempo, _current_frame_rate) * beats_left;
+			}
+
+			int clickbeat = 0;
+			framepos_t cf = _transport_frame - _count_in_samples;
+			while (cf < _transport_frame) {
+				add_click (cf - _worst_track_latency, clickbeat == 0);
+				cf += dt;
+				clickbeat = fmod (clickbeat + 1, div);
+			}
+		}
 	}
 
 	DEBUG_TRACE (DEBUG::Transport, string_compose ("send TSC4 with speed = %1\n", _transport_speed));