Fix loop recording alignment

DiskWriter::transport_looped() is called from the session
when engine loops. This does not take local disk-reader run()
latency offset into account.

finish_capture() needs to be postponed until the disk-writer
itself reaches the loop-position. This is achieved by
postponing loop() and calling it once loop-length of samples
has been captured.

This works because engaging loop always seeks to the loop-position
and first loop resets _capture_captured.

2 files changed, 41 insertions, 9 deletions

diff --git a/libs/ardour/ardour/disk_writer.h b/libs/ardour/ardour/disk_writer.h
index c17c2e539e..fab54e2404 100644
--- a/libs/ardour/ardour/disk_writer.h
+++ b/libs/ardour/ardour/disk_writer.h
@@ -169,6 +169,8 @@ private:
 	void check_record_status (samplepos_t transport_sample, double speed, bool can_record);
 	void finish_capture (boost::shared_ptr<ChannelList> c);
 
+	void loop (samplepos_t);
+
 	CaptureInfos                 capture_info;
 	mutable Glib::Threads::Mutex capture_info_lock;
 
@@ -187,6 +189,9 @@ private:
 	volatile gint _num_captured_loops;
 	samplepos_t   _accumulated_capture_offset;
 
+	bool          _transport_looped;
+	samplepos_t   _transport_loop_sample;
+
 	boost::shared_ptr<SMFSource> _midi_write_source;
 
 	std::list<boost::shared_ptr<Source> >            _last_capture_sources;
diff --git a/libs/ardour/disk_writer.cc b/libs/ardour/disk_writer.cc
index cb62f932b6..cddfe7b09b 100644
--- a/libs/ardour/disk_writer.cc
+++ b/libs/ardour/disk_writer.cc
@@ -59,6 +59,8 @@ DiskWriter::DiskWriter (Session& s, string const & str, DiskIOProcessor::Flag f)
 	, _samples_pending_write (0)
 	, _num_captured_loops (0)
 	, _accumulated_capture_offset (0)
+	, _transport_looped (false)
+	, _transport_loop_sample (0)
 	, _gui_feed_buffer(AudioEngine::instance()->raw_buffer_size (DataType::MIDI))
 {
 	DiskIOProcessor::init ();
@@ -397,6 +399,29 @@ DiskWriter::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_samp
 
 	_need_butler = false;
 
+	const Location* const loop_loc    = _loop_location;
+	samplepos_t           loop_start  = 0;
+	samplepos_t           loop_end    = 0;
+	samplepos_t           loop_length = 0;
+
+	if (_transport_looped && _capture_captured == 0) {
+		_transport_looped = false;
+	}
+
+	if (loop_loc) {
+		get_location_times (loop_loc, &loop_start, &loop_end, &loop_length);
+
+		if (_was_recording && _transport_looped && _capture_captured >= loop_length) {
+			samplecnt_t remain = _capture_captured - loop_length;
+			_capture_captured = loop_length;
+			loop (_transport_loop_sample);
+			_capture_captured = remain;
+		}
+
+	} else {
+		_transport_looped = false;
+	}
+
 #ifndef NDEBUG
 	if (speed != 0 && re) {
 		DEBUG_TRACE (DEBUG::CaptureAlignment, string_compose ("%1: run() start: %2 end: %3 NF: %4\n", _name, start_sample, end_sample, nframes));
@@ -418,15 +443,6 @@ DiskWriter::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_samp
 		_last_recordable_sample = max_samplepos;
 	}
 
-	const Location* const loop_loc    = _loop_location;
-	samplepos_t           loop_start  = 0;
-	samplepos_t           loop_end    = 0;
-	samplepos_t           loop_length = 0;
-
-	if (loop_loc) {
-		get_location_times (loop_loc, &loop_start, &loop_end, &loop_length);
-	}
-
 	if (nominally_recording || (re && _was_recording && _session.get_record_enabled() && punch_in)) {
 
 		Evoral::OverlapType ot = Evoral::coverage (_first_recordable_sample, _last_recordable_sample, start_sample, end_sample);
@@ -1318,6 +1334,17 @@ DiskWriter::transport_stopped_wallclock (struct tm& when, time_t twhen, bool abo
 void
 DiskWriter::transport_looped (samplepos_t transport_sample)
 {
+	if (_capture_captured) {
+		_transport_looped = true;
+		_transport_loop_sample = transport_sample;
+		_first_recordable_sample = transport_sample;
+	}
+}
+
+void
+DiskWriter::loop (samplepos_t transport_sample)
+{
+	_transport_looped = false;
 	if (_was_recording) {
 		// all we need to do is finish this capture, with modified capture length
 		boost::shared_ptr<ChannelList> c = channels.reader();