From 4998b2711b510141561f444de7dca99ba2327fd0 Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Tue, 14 Sep 2021 21:33:08 +0200
Subject: [PATCH] Amend f301e692a: expose compensated port-latency

Retain min/max when copying inherited latency from
connected ports.

When there is a direct connection port A out -> port B in,
min/max latency range should be retained in direction
of signal flow.

Ardour can only adjust latency in reverse direction of signal flow
to match min = max with an internal delay-line. ie set playback
latency of an input port, or capture latency of an output port.
---
 libs/ardour/ardour/io.h |  1 +
 libs/ardour/io.cc       | 27 +++++++++++++++++++++++++++
 libs/ardour/route.cc    |  8 ++++----
 3 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/libs/ardour/ardour/io.h b/libs/ardour/ardour/io.h
index 4784b4205d..5115310540 100644
--- a/libs/ardour/ardour/io.h
+++ b/libs/ardour/ardour/io.h
@@ -124,6 +124,7 @@ public:
 
 	void set_private_port_latencies (samplecnt_t value, bool playback);
 	void set_public_port_latencies (samplecnt_t value, bool playback) const;
+	void set_public_port_latency_from_connections () const;
 
 	PortSet& ports() { return _ports; }
 	const PortSet& ports() const { return _ports; }
diff --git a/libs/ardour/io.cc b/libs/ardour/io.cc
index 57bbade9de..5e6af7fdd7 100644
--- a/libs/ardour/io.cc
+++ b/libs/ardour/io.cc
@@ -1261,6 +1261,33 @@ IO::set_private_port_latencies (samplecnt_t value, bool playback)
 	}
 }
 
+void
+IO::set_public_port_latency_from_connections () const
+{
+	/* get min/max of connected up/downstream ports */
+	bool connected = false;
+	bool playback = _direction == Output;
+	LatencyRange lr;
+	lr.min = ~((pframes_t) 0);
+	lr.max = 0;
+
+	for (PortSet::const_iterator i = _ports.begin(); i != _ports.end(); ++i) {
+		if (i->connected()) {
+			connected = true;
+		}
+		i->collect_latency_from_backend (lr, playback);
+	}
+
+	if (!connected) {
+		/* if output is not connected to anything, use private latency */
+		lr.min = lr.max = latency ();
+	}
+
+	for (PortSet::const_iterator i = _ports.begin (); i != _ports.end(); ++i) {
+		 i->set_public_latency_range (lr, playback);
+	}
+}
+
 void
 IO::set_public_port_latencies (samplecnt_t value, bool playback) const
 {
diff --git a/libs/ardour/route.cc b/libs/ardour/route.cc
index 092c8b72eb..6efc03c0aa 100644
--- a/libs/ardour/route.cc
+++ b/libs/ardour/route.cc
@@ -5002,17 +5002,17 @@ Route::set_public_port_latencies (samplecnt_t value, bool playback, bool with_la
 	 * latency compensation into account.
 	 */
 	if (playback) {
-		_output->set_public_port_latencies (_output->latency (), playback);
+		_output->set_public_port_latency_from_connections ();
 		if (_delayline && with_latcomp) {
 			value += _delayline->delay ();
 		}
-		_input->set_public_port_latencies (value, playback);
+		_input->set_public_port_latencies (value, true);
 	} else {
-		_input->set_public_port_latencies (_input->latency(), playback);
+		_input->set_public_port_latency_from_connections ();
 		if (_delayline && with_latcomp) {
 			value += _delayline->delay ();
 		}
-		_output->set_public_port_latencies (value, playback);
+		_output->set_public_port_latencies (value, false);
 	}
 
 }