From 66a8776f98d41ebcdd9b0413001d397ad0cb8eff Mon Sep 17 00:00:00 2001
From: Paul Davis <paul@linuxaudiosystems.com>
Date: Thu, 19 Jun 2025 13:50:37 -0600
Subject: [PATCH] fix InternalSend (and InterntalReturn) to allow fade out/MIDI
 mute

previously, as soon as the Send is disabled, it would short-circuit ::run(),
preventing the fade to zero to take effect. Now, the send will run until the
effective gain reaches zero, and the return will collect data from it until it
is fully deactivated.
---
 libs/ardour/ardour/internal_send.h |  1 +
 libs/ardour/internal_return.cc     |  2 +-
 libs/ardour/internal_send.cc       | 24 +++++++++++++++++++-----
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/libs/ardour/ardour/internal_send.h b/libs/ardour/ardour/internal_send.h
index 7e814a3a41..a355ac22a0 100644
--- a/libs/ardour/ardour/internal_send.h
+++ b/libs/ardour/ardour/internal_send.h
@@ -45,6 +45,7 @@ public:
 	bool can_support_io_configuration (const ChanCount& in, ChanCount& out);
 	bool configure_io (ChanCount in, ChanCount out);
 	int  set_block_size (pframes_t);
+	bool actually_active() const { return _active; }
 
 	std::shared_ptr<Route> source_route() const { return _send_from; }
 	std::shared_ptr<Route> target_route() const { return _send_to; }
diff --git a/libs/ardour/internal_return.cc b/libs/ardour/internal_return.cc
index a9cfe32d38..a805f71f06 100644
--- a/libs/ardour/internal_return.cc
+++ b/libs/ardour/internal_return.cc
@@ -48,7 +48,7 @@ InternalReturn::run (BufferSet& bufs, samplepos_t /*start_sample*/, samplepos_t
 	}
 
 	for (auto & send : _sends) {
-		if (send->active () && (!send->source_route() || send->source_route()->active())) {
+		if ((send->active() || send->actually_active()) && (!send->source_route() || send->source_route()->active())) {
 			bufs.merge_from (send->get_buffers(), nframes);
 		}
 	}
diff --git a/libs/ardour/internal_send.cc b/libs/ardour/internal_send.cc
index 07a1495520..8f0c077ed8 100644
--- a/libs/ardour/internal_send.cc
+++ b/libs/ardour/internal_send.cc
@@ -49,6 +49,8 @@ using namespace std;
 
 PBD::Signal<void(pframes_t)> InternalSend::CycleStart;
 
+#define GAIN_COEFF_DELTA (1e-5)
+
 InternalSend::InternalSend (Session&                      s,
                             std::shared_ptr<Pannable>   p,
                             std::shared_ptr<MuteMaster> mm,
@@ -213,7 +215,20 @@ InternalSend::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_sa
 {
 	automation_run (start_sample, nframes);
 
-	if (!check_active() || !_send_to) {
+	/* Do not use check_active() here, because we need to continue running
+	 * until the gain has gone to zero.
+	 */
+
+	if (!_send_to) {
+		_meter->reset ();
+		return;
+	}
+
+	/* main gain control: * mute & bypass/enable */
+	const gain_t tgain = target_gain ();
+	const bool converged = fabsf (_current_gain - tgain) < GAIN_COEFF_DELTA;
+
+	if ((tgain == GAIN_COEFF_ZERO) && converged) {
 		_meter->reset ();
 		return;
 	}
@@ -317,9 +332,6 @@ InternalSend::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_sa
 		}
 	}
 
-	/* main gain control: * mute & bypass/enable */
-	gain_t tgain = target_gain ();
-
 	if (tgain != _current_gain) {
 		/* target gain has changed, fade in/out */
 		_current_gain = Amp::apply_gain (mixbufs, _session.nominal_sample_rate (), nframes, _current_gain, tgain);
@@ -353,7 +365,9 @@ InternalSend::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_sa
 
 	_thru_delay->run (bufs, start_sample, end_sample, speed, nframes, true);
 
-	/* target will pick up our output when it is ready */
+	if (converged) {
+		_active = _pending_active;
+	}
 }
 
 void