Prepare to allow to disable latency-compensation

Previously "zero custom/user latency" meant "default plugin latency".
This is now saved in a separate boolean allowing a user to reduce a
processor's latency to zero.

This also prepares for a global switch to use zero latency throughout
the whole session.

11 files changed, 119 insertions, 52 deletions

diff --git a/libs/ardour/ardour/latent.h b/libs/ardour/ardour/latent.h
index c4464f7ba4..b7d9a3fcd5 100644
--- a/libs/ardour/ardour/latent.h
+++ b/libs/ardour/ardour/latent.h
@@ -26,27 +26,61 @@
 namespace ARDOUR {
 
 class LIBARDOUR_API Latent {
-  public:
+public:
 	Latent() : _user_latency (0) {}
 	virtual ~Latent() {}
 
 	virtual samplecnt_t signal_latency() const = 0;
-	samplecnt_t user_latency () const { return _user_latency; }
 
+	/* effective latency to be used while processing */
 	samplecnt_t effective_latency() const {
-		if (_user_latency) {
+		if (_zero_latency) {
+			return 0;
+		} else if (_use_user_latency) {
 			return _user_latency;
 		} else {
 			return signal_latency ();
 		}
 	}
 
-	virtual void set_user_latency (samplecnt_t val) { _user_latency = val; }
+	/* custom user-set latency, if any */
+	samplecnt_t user_latency () const {
+		if (_use_user_latency) {
+			return _user_latency;
+		} else {
+			return 0;
+		}
+	}
+
+	void unset_user_latency () {
+		_use_user_latency = false;
+		_user_latency = 0;
+	}
+
+	virtual void set_user_latency (samplecnt_t val) {
+		_use_user_latency = true;
+		_user_latency = val;
+	}
+
+	static void force_zero_latency (bool en) {
+		_zero_latency = en;
+	}
 
-  protected:
-	samplecnt_t           _user_latency;
+	static bool zero_latency () {
+		return _zero_latency;
+	}
+
+protected:
+	int  set_state (const XMLNode& node, int version);
+	void add_state (XMLNode*) const;
+
+private:
+	samplecnt_t _use_user_latency;
+	samplecnt_t _user_latency;
+	static bool _zero_latency;
 };
 
-}
+} /* namespace */
+
 
 #endif /* __ardour_latent_h__*/
diff --git a/libs/ardour/io.cc b/libs/ardour/io.cc
index 99cd41657f..59e452633a 100644
--- a/libs/ardour/io.cc
+++ b/libs/ardour/io.cc
@@ -536,7 +536,7 @@ IO::state ()
 		node->add_child_nocopy (*pnode);
 	}
 
-	node->set_property (X_("user-latency"), _user_latency);
+	Latent::add_state (node);
 
 	return *node;
 }
@@ -597,7 +597,7 @@ IO::set_state (const XMLNode& node, int version)
 		ConnectingLegal.connect_same_thread (connection_legal_c, boost::bind (&IO::connecting_became_legal, this));
 	}
 
-	node.get_property ("user-latency", _user_latency);
+	Latent::set_state (node, version);
 
 	return 0;
 }
diff --git a/libs/ardour/ladspa_plugin.cc b/libs/ardour/ladspa_plugin.cc
index be0edee8b5..bb59c6ec55 100644
--- a/libs/ardour/ladspa_plugin.cc
+++ b/libs/ardour/ladspa_plugin.cc
@@ -528,10 +528,6 @@ LadspaPlugin::describe_parameter (Evoral::Parameter which)
 ARDOUR::samplecnt_t
 LadspaPlugin::signal_latency () const
 {
-	if (_user_latency) {
-		return _user_latency;
-	}
-
 	if (_latency_control_port) {
 		return (samplecnt_t) floor (*_latency_control_port);
 	} else {
diff --git a/libs/ardour/latent.cc b/libs/ardour/latent.cc
new file mode 100644
index 0000000000..44ec0e7d30
--- /dev/null
+++ b/libs/ardour/latent.cc
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2018 Robin Gareus <robin@gareus.org>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+#include "pbd/xml++.h"
+
+#include "ardour/latent.h"
+
+using namespace ARDOUR;
+
+bool ARDOUR::Latent::_zero_latency = false;
+
+int
+Latent::set_state (const XMLNode& node, int version)
+{
+	node.get_property ("user-latency", _user_latency);
+	if (!node.get_property ("use-user-latency", _use_user_latency)) {
+		_use_user_latency = _user_latency > 0;
+	}
+	return 0;
+}
+
+void
+Latent::add_state (XMLNode* node) const
+{
+	node->set_property ("user-latency", _user_latency);
+	node->set_property ("use-user-latency", _use_user_latency);
+}
diff --git a/libs/ardour/plugin_insert.cc b/libs/ardour/plugin_insert.cc
index 3435fd2241..a4a5ad1972 100644
--- a/libs/ardour/plugin_insert.cc
+++ b/libs/ardour/plugin_insert.cc
@@ -651,8 +651,10 @@ PluginInsert::activate ()
 	if (!owner ()) {
 		return;
 	}
-	if (_plugin_signal_latency != signal_latency ()) {
-		_plugin_signal_latency = signal_latency ();
+
+	const samplecnt_t l = effective_latency ();
+	if (_plugin_signal_latency != l) {
+		_plugin_signal_latency = l;
 		latency_changed ();
 	}
 }
@@ -671,8 +673,10 @@ PluginInsert::deactivate ()
 	for (Plugins::iterator i = _plugins.begin(); i != _plugins.end(); ++i) {
 		(*i)->deactivate ();
 	}
-	if (_plugin_signal_latency != signal_latency ()) {
-		_plugin_signal_latency = signal_latency ();
+
+	const samplecnt_t l = effective_latency ();
+	if (_plugin_signal_latency != l) {
+		_plugin_signal_latency = l;
 		latency_changed ();
 	}
 }
@@ -1063,8 +1067,9 @@ PluginInsert::connect_and_run (BufferSet& bufs, samplepos_t start, samplepos_t e
 		}
 	}
 
-	if (_plugin_signal_latency != signal_latency ()) {
-		_plugin_signal_latency = signal_latency ();
+	const samplecnt_t l = effective_latency ();
+	if (_plugin_signal_latency != l) {
+		_plugin_signal_latency = l;
 		latency_changed ();
 	}
 }
@@ -2906,11 +2911,7 @@ PluginInsert::signal_latency() const
 	if (!_pending_active) {
 		return 0;
 	}
-	if (_user_latency) {
-		return _user_latency;
-	}
-
-	return _plugins[0]->signal_latency ();
+	return plugin_latency ();
 }
 
 ARDOUR::PluginType
diff --git a/libs/ardour/port_insert.cc b/libs/ardour/port_insert.cc
index a6a05cede7..fd7d220d88 100644
--- a/libs/ardour/port_insert.cc
+++ b/libs/ardour/port_insert.cc
@@ -79,8 +79,8 @@ PortInsert::start_latency_detection ()
 void
 PortInsert::stop_latency_detection ()
 {
-        _latency_flush_samples = signal_latency() + _session.engine().samples_per_cycle();
-        _latency_detect = false;
+	_latency_flush_samples = effective_latency() + _session.engine().samples_per_cycle();
+	_latency_detect = false;
 }
 
 void
@@ -232,11 +232,11 @@ PortInsert::signal_latency() const
 	   need to take that into account too.
 	*/
 
-        if (_measured_latency == 0) {
-                return _session.engine().samples_per_cycle() + _input->signal_latency();
-        } else {
-                return _measured_latency;
-        }
+	if (_measured_latency == 0) {
+		return _session.engine().samples_per_cycle() + _input->effective_latency ();
+	} else {
+		return _measured_latency;
+	}
 }
 
 /** Caller must hold process lock */
diff --git a/libs/ardour/processor.cc b/libs/ardour/processor.cc
index 39c3d68ad7..9f799a5060 100644
--- a/libs/ardour/processor.cc
+++ b/libs/ardour/processor.cc
@@ -146,7 +146,7 @@ Processor::state ()
 		}
 	}
 
-	node->set_property("user-latency", _user_latency);
+	Latent::add_state (node);
 
 	return *node;
 }
@@ -252,7 +252,7 @@ Processor::set_state (const XMLNode& node, int version)
 		}
 	}
 
-	node.get_property ("user-latency", _user_latency);
+	Latent::set_state (node, version);
 
 	return 0;
 }
diff --git a/libs/ardour/route.cc b/libs/ardour/route.cc
index a1f356351c..b48b3b5a2b 100644
--- a/libs/ardour/route.cc
+++ b/libs/ardour/route.cc
@@ -502,7 +502,7 @@ Route::process_output_buffers (BufferSet& bufs,
 		 * So there can be cases where adding up all latencies may not equal _signal_latency.
 		 */
 		if ((*i)->active ()) {
-			latency += (*i)->signal_latency ();
+			latency += (*i)->effective_latency ();
 		}
 
 		if (re_inject_oob_data) {
@@ -569,7 +569,7 @@ Route::bounce_process (BufferSet& buffers, samplepos_t start, samplecnt_t nframe
 		if (!(*i)->does_routing() && !boost::dynamic_pointer_cast<PeakMeter>(*i)) {
 			(*i)->run (buffers, start - latency, start - latency + nframes, 1.0, nframes, true);
 			buffers.set_count ((*i)->output_streams());
-			latency += (*i)->signal_latency ();
+			latency += (*i)->effective_latency ();
 		}
 
 		if ((*i) == endpoint) {
@@ -598,7 +598,7 @@ Route::bounce_get_latency (boost::shared_ptr<Processor> endpoint,
 			break;
 		}
 		if (!(*i)->does_routing() && !boost::dynamic_pointer_cast<PeakMeter>(*i)) {
-			latency += (*i)->signal_latency ();
+			latency += (*i)->effective_latency ();
 		}
 		if ((*i) == endpoint) {
 			break;
@@ -1129,7 +1129,7 @@ Route::add_processors (const ProcessorList& others, boost::shared_ptr<Processor>
 			}
 		}
 
-		_output->set_user_latency (0);
+		_output->unset_user_latency ();
 	}
 
 	reset_instrument_info ();
@@ -1448,7 +1448,7 @@ Route::remove_processor (boost::shared_ptr<Processor> processor, ProcessorStream
 				++i;
 			}
 
-			_output->set_user_latency (0);
+			_output->unset_user_latency ();
 		}
 
 		if (!removed) {
@@ -1576,7 +1576,7 @@ Route::replace_processor (boost::shared_ptr<Processor> old, boost::shared_ptr<Pr
 		}
 
 		sub->ActiveChanged.connect_same_thread (*this, boost::bind (&Session::update_latency_compensation, &_session, false));
-		_output->set_user_latency (0);
+		_output->unset_user_latency ();
 	}
 
 	reset_instrument_info ();
@@ -1648,7 +1648,7 @@ Route::remove_processors (const ProcessorList& to_be_deleted, ProcessorStreams*
 			return 0;
 		}
 
-		_output->set_user_latency (0);
+		_output->unset_user_latency ();
 
 		if (configure_processors_unlocked (err, &lm)) {
 			pstate.restore ();
@@ -4038,7 +4038,7 @@ Route::update_signal_latency (bool apply_to_delayline)
 	Glib::Threads::RWLock::ReaderLock lm (_processor_lock);
 
 	samplecnt_t l_in  = 0;
-	samplecnt_t l_out = _output->user_latency();
+	samplecnt_t l_out = _output->effective_latency ();
 	for (ProcessorList::reverse_iterator i = _processors.rbegin(); i != _processors.rend(); ++i) {
 		if (boost::shared_ptr<Send> snd = boost::dynamic_pointer_cast<Send> (*i)) {
 			snd->set_delay_in (l_out + _output->latency());
@@ -4052,8 +4052,8 @@ Route::update_signal_latency (bool apply_to_delayline)
 			}
 		}
 		(*i)->set_output_latency (l_out);
-		if ((*i)->active ()) {
-			l_out += (*i)->signal_latency ();
+		if ((*i)->active ()) { // XXX
+			l_out += (*i)->effective_latency ();
 		}
 	}
 
@@ -4087,7 +4087,7 @@ Route::update_signal_latency (bool apply_to_delayline)
 		(*i)->set_playback_offset (_signal_latency + _output->latency ());
 		(*i)->set_capture_offset (_input->latency ());
 		if ((*i)->active ()) {
-			l_in += (*i)->signal_latency ();
+			l_in += (*i)->effective_latency ();
 		}
 	}
 
@@ -4644,7 +4644,7 @@ Route::set_private_port_latencies (bool playback) const
 	for (ProcessorList::const_iterator i = _processors.begin(); i != _processors.end(); ++i) {
 
 		if ((*i)->active ()) {
-			own_latency += (*i)->signal_latency ();
+			own_latency += (*i)->effective_latency ();
 		}
 	}
 
diff --git a/libs/ardour/send.cc b/libs/ardour/send.cc
index a9b8f2b135..aef54150f8 100644
--- a/libs/ardour/send.cc
+++ b/libs/ardour/send.cc
@@ -141,9 +141,6 @@ Send::signal_latency () const
 	if (!_pending_active) {
 		 return 0;
 	}
-	if (_user_latency) {
-		return _user_latency;
-	}
 	if (_delay_out > _delay_in) {
 		return _delay_out - _delay_in;
 	}
diff --git a/libs/ardour/vst_plugin.cc b/libs/ardour/vst_plugin.cc
index 4183283bff..e4968b5158 100644
--- a/libs/ardour/vst_plugin.cc
+++ b/libs/ardour/vst_plugin.cc
@@ -645,10 +645,6 @@ VSTPlugin::describe_parameter (Evoral::Parameter param)
 samplecnt_t
 VSTPlugin::signal_latency () const
 {
-	if (_user_latency) {
-		return _user_latency;
-	}
-
 #if ( defined(__x86_64__) || defined(_M_X64) )
 	return *((int32_t *) (((char *) &_plugin->flags) + 24)); /* initialDelay */
 #else
diff --git a/libs/ardour/wscript b/libs/ardour/wscript
index 87238374d1..a8bb9d50d3 100644
--- a/libs/ardour/wscript
+++ b/libs/ardour/wscript
@@ -113,6 +113,7 @@ libardour_sources = [
         'io_processor.cc',
         'kmeterdsp.cc',
         'ladspa_plugin.cc',
+        'latent.cc',
         'legatize.cc',
         'location.cc',
         'location_importer.cc',