Add a ReadOnlyControl parameter abstraction

This allows to pass a sperici Controllable alike instance around without
relying on directly exposing the Plugin instance and parameter-id.

libs/ardour/ardour/plugin_insert.h

@@ -34,6 +34,7 @@
 #include "ardour/parameter_descriptor.h"
 #include "ardour/plugin.h"
 #include "ardour/processor.h"
+#include "ardour/readonly_control.h"
 #include "ardour/sidechain.h"
 #include "ardour/automation_control.h"
 
@@ -243,6 +244,8 @@ class LIBARDOUR_API PluginInsert : public Processor
 
 	PluginType type ();
 
+	boost::shared_ptr<ReadOnlyControl> control_output (uint32_t) const;
+
 	std::string describe_parameter (Evoral::Parameter param);
 
 	framecnt_t signal_latency () const;
@@ -375,6 +378,9 @@ class LIBARDOUR_API PluginInsert : public Processor
 	bool _latency_changed;
 	uint32_t _bypass_port;
 
+	typedef std::map<uint32_t, boost::shared_ptr<ReadOnlyControl> >CtrlOutMap;
+	CtrlOutMap _control_outputs;
+
 	void preset_load_set_value (uint32_t, float);
 };
 

libs/ardour/ardour/readonly_control.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2017 Robin Gareus <robin@gareus.org>
+ * Copyright (C) 2000, 2007 Paul Davis
+ *
+ * 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.
+ */
+
+#ifndef __ardour_readonly_control_h__
+#define __ardour_readonly_control_h__
+
+#include <boost/weak_ptr.hpp>
+
+namespace ARDOUR {
+
+class Plugin;
+
+class LIBARDOUR_API ReadOnlyControl : public PBD::Destructible
+{
+public:
+	ReadOnlyControl (boost::shared_ptr<Plugin> p, uint32_t pnum);
+
+	double get_parameter () const;
+	std::string describe_parameter ();
+
+private:
+	boost::weak_ptr<Plugin> _plugin;
+	uint32_t _parameter_num;
+};
+
+} // namespace ARDOUR
+
+#endif /* __ardour_readonly_control_h__ */

libs/ardour/plugin_insert.cc

@@ -98,6 +98,9 @@ PluginInsert::PluginInsert (Session& s, boost::shared_ptr<Plugin> plug)
 
 PluginInsert::~PluginInsert ()
 {
+	for (CtrlOutMap::const_iterator i = _control_outputs.begin(); i != _control_outputs.end(); ++i) {
+		boost::dynamic_pointer_cast<ReadOnlyControl>(i->second)->drop_references ();
+	}
 }
 
 void
@@ -452,7 +455,11 @@ PluginInsert::create_automatable_parameters ()
 	set<Evoral::Parameter> a = _plugins.front()->automatable ();
 
 	for (uint32_t i = 0; i < plugin->parameter_count(); ++i) {
-		if (!plugin->parameter_is_control (i) || !plugin->parameter_is_input (i)) {
+		if (!plugin->parameter_is_control (i)) {
+			continue;
+		}
+		if (!plugin->parameter_is_input (i)) {
+			_control_outputs[i] = boost::shared_ptr<ReadOnlyControl> (new ReadOnlyControl (plugin, i));
 			continue;
 		}
 		Evoral::Parameter param (PluginAutomation, 0, i);
@@ -2803,6 +2810,16 @@ PluginInsert::set_parameter_state_2X (const XMLNode& node, int version)
 	}
 }
 
+boost::shared_ptr<ReadOnlyControl>
+PluginInsert::control_output (uint32_t num) const
+{
+	CtrlOutMap::const_iterator i = _control_outputs.find (num);
+	if (i == _control_outputs.end ()) {
+		return boost::shared_ptr<ReadOnlyControl> ();
+	} else {
+		return (*i).second;
+	}
+}
 
 string
 PluginInsert::describe_parameter (Evoral::Parameter param)

libs/ardour/readonly_control.cc

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2017 Robin Gareus <robin@gareus.org>
+ * Copyright (C) 2000, 2007 Paul Davis
+ *
+ * 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/destructible.h"
+
+#include "ardour/plugin.h"
+#include "ardour/readonly_control.h"
+
+using namespace ARDOUR;
+
+ReadOnlyControl::ReadOnlyControl (boost::shared_ptr<Plugin> p, uint32_t pnum)
+		: _plugin (boost::weak_ptr<Plugin> (p))
+		, _parameter_num (pnum)
+{ }
+
+double
+ReadOnlyControl::get_parameter () const
+{
+	boost::shared_ptr<Plugin> p = _plugin.lock();
+	if (p) {
+		return p->get_parameter (_parameter_num);
+	}
+	return 0;
+}
+
+std::string
+ReadOnlyControl::describe_parameter ()
+{
+	boost::shared_ptr<Plugin> p = _plugin.lock();
+	if (p) {
+		return p->describe_parameter (Evoral::Parameter (ARDOUR::PluginAutomation, 0, _parameter_num));
+	}
+	return "";
+}

libs/ardour/wscript

@@ -178,6 +178,7 @@ libardour_sources = [
         'progress.cc',
         'quantize.cc',
         'rc_configuration.cc',
+        'readonly_control.cc',
         'recent_sessions.cc',
         'record_enable_control.cc',
         'record_safe_control.cc',