Catch up with plugin property changes (LV2/JUCE)

When a user changes a value in the Plugin GUI, JUCE informs the
DSP behind the host's back, and later informs the host from the
DSP (realtime) thread, by sending patch:Set messages from the DSP
back to the host/UI.

This is really bad practice, particularly since the plugin does
no even use LV2 instance access, or LV2 data access features.

libs/ardour/ardour/io_plug.h

@@ -118,6 +118,7 @@ private:
 	std::string ensure_io_name (std::string) const;
 	void create_parameters ();
 	void parameter_changed_externally (uint32_t, float);
+	void property_changed_externally (uint32_t, Variant);
 
 	void setup ();
 

libs/ardour/ardour/plug_insert_base.h

@@ -100,6 +100,7 @@ public:
 		                       std::shared_ptr<AutomationList> list = std::shared_ptr<AutomationList> ());
 
 		virtual double get_value (void) const;
+		void           catch_up_with_external_value (double val);
 		XMLNode&       get_state () const;
 
 	protected:

libs/ardour/ardour/plugin_insert.h

@@ -276,6 +276,7 @@ private:
 	PluginInsert (const PluginInsert&);
 
 	void parameter_changed_externally (uint32_t, float);
+	void property_changed_externally (uint32_t which, Variant);
 
 	void set_parameter (Evoral::Parameter param, float val, sampleoffset_t);
 

libs/ardour/ardour/region_fx_plugin.h

@@ -165,6 +165,7 @@ private:
 	bool check_inplace ();
 	void create_parameters ();
 	void parameter_changed_externally (uint32_t, float);
+	void property_changed_externally (uint32_t, Variant);
 	void automation_run (samplepos_t start, pframes_t nframes);
 	bool find_next_event (timepos_t const& start, timepos_t const& end, Evoral::ControlEvent& next_event) const;
 	void start_touch (uint32_t param_id);

libs/ardour/io_plug.cc

@@ -256,6 +256,7 @@ IOPlug::setup ()
 
 	 _plugin->reconfigure_io (_n_in, aux_in, _n_out);
 	 _plugin->ParameterChangedExternally.connect_same_thread (*this, std::bind (&IOPlug::parameter_changed_externally, this, _1, _2));
+	 _plugin->PropertyChanged.connect_same_thread (*this, std::bind (&IOPlug::property_changed_externally, this, _1, _2));
 	 _plugin->activate ();
 	 _plugin->set_insert (this, 0);
 }
@@ -372,6 +373,17 @@ IOPlug::parameter_changed_externally (uint32_t which, float val)
 	}
 }
 
+void
+IOPlug::property_changed_externally (uint32_t which, Variant val)
+{
+	std::shared_ptr<Evoral::Control>        c  = control (Evoral::Parameter (PluginPropertyAutomation, 0, which));
+	std::shared_ptr<PluginPropertyControl>  pc = std::dynamic_pointer_cast<PluginPropertyControl> (c);
+
+	if (pc) {
+		pc->catch_up_with_external_value (val.to_double ());
+	}
+}
+
 int
 IOPlug::set_block_size (pframes_t n_samples)
 {

libs/ardour/plug_insert_base.cc

@@ -393,6 +393,14 @@ PlugInsertBase::PluginPropertyControl::actually_set_value (double user_val, Cont
 	AutomationControl::actually_set_value (user_val, gcd);
 }
 
+void
+PlugInsertBase::PluginPropertyControl::catch_up_with_external_value (double user_val)
+{
+	if (user_val != Control::get_double ()) {
+		PluginPropertyControl::actually_set_value (user_val, Controllable::NoGroup);
+	}
+}
+
 XMLNode&
 PlugInsertBase::PluginPropertyControl::get_state () const
 {

libs/ardour/plugin_insert.cc

@@ -660,6 +660,39 @@ PluginInsert::parameter_changed_externally (uint32_t which, float val)
 	}
 }
 
+void
+PluginInsert::property_changed_externally (uint32_t which, Variant val)
+{
+	std::shared_ptr<Evoral::Control>        c  = control (Evoral::Parameter (PluginPropertyAutomation, 0, which));
+	std::shared_ptr<PluginPropertyControl>  pc = std::dynamic_pointer_cast<PluginPropertyControl> (c);
+
+	if (pc) {
+		pc->catch_up_with_external_value (val.to_double ());
+	}
+
+	/* Second propagation: tell all plugins except the first to
+	 * update the value of this parameter. For sane plugin APIs,
+	 * there are no other plugins, so this is a no-op in those
+	 * cases.
+	 */
+
+	Plugins::iterator i = _plugins.begin ();
+
+	/* don't set the first plugin, just all the slaves */
+
+	if (i != _plugins.end ()) {
+		++i;
+		for (; i != _plugins.end (); ++i) {
+			(*i)->set_property (which, val);
+		}
+	}
+
+	std::shared_ptr<Plugin> iasp = _impulseAnalysisPlugin.lock();
+	if (iasp) {
+		iasp->set_property (which, val);
+	}
+}
+
 int
 PluginInsert::set_block_size (pframes_t nframes)
 {
@@ -3021,6 +3054,7 @@ PluginInsert::add_plugin (std::shared_ptr<Plugin> plugin)
 		/* first (and probably only) plugin instance - connect to relevant signals */
 
 		plugin->ParameterChangedExternally.connect_same_thread (*this, std::bind (&PluginInsert::parameter_changed_externally, this, _1, _2));
+		plugin->PropertyChanged.connect_same_thread (*this, std::bind (&PluginInsert::property_changed_externally, this, _1, _2));
 		plugin->StartTouch.connect_same_thread (*this, std::bind (&PluginInsert::start_touch, this, _1));
 		plugin->EndTouch.connect_same_thread (*this, std::bind (&PluginInsert::end_touch, this, _1));
 		_custom_sinks = plugin->get_info()->n_inputs;

libs/ardour/region_fx_plugin.cc

@@ -430,6 +430,7 @@ RegionFxPlugin::add_plugin (std::shared_ptr<Plugin> plugin)
 	if (_plugins.empty ()) {
 		/* first (and probably only) plugin instance - connect to relevant signals */
 		plugin->ParameterChangedExternally.connect_same_thread (*this, std::bind (&RegionFxPlugin::parameter_changed_externally, this, _1, _2));
+		plugin->PropertyChanged.connect_same_thread (*this, std::bind (&RegionFxPlugin::property_changed_externally, this, _1, _2));
 		plugin->StartTouch.connect_same_thread (*this, std::bind (&RegionFxPlugin::start_touch, this, _1));
 		plugin->EndTouch.connect_same_thread (*this, std::bind (&RegionFxPlugin::end_touch, this, _1));
 	}
@@ -695,6 +696,34 @@ RegionFxPlugin::parameter_changed_externally (uint32_t which, float val)
 	}
 }
 
+void
+RegionFxPlugin::property_changed_externally (uint32_t which, Variant val)
+{
+	std::shared_ptr<Evoral::Control>        c  = control (Evoral::Parameter (PluginPropertyAutomation, 0, which));
+	std::shared_ptr<PluginPropertyControl>  pc = std::dynamic_pointer_cast<PluginPropertyControl> (c);
+
+	if (pc) {
+		pc->catch_up_with_external_value (val.to_double ());
+	}
+
+	/* Second propagation: tell all plugins except the first to
+	 * update the value of this parameter. For sane plugin APIs,
+	 * there are no other plugins, so this is a no-op in those
+	 * cases.
+	 */
+
+	Plugins::iterator i = _plugins.begin ();
+
+	/* don't set the first plugin, just all the slaves */
+
+	if (i != _plugins.end ()) {
+		++i;
+		for (; i != _plugins.end (); ++i) {
+			(*i)->set_property (which, val);
+		}
+	}
+}
+
 std::string
 RegionFxPlugin::describe_parameter (Evoral::Parameter param)
 {