implement lv2:designation processing#enable (for bypass ports)

libs/ardour/ardour/lv2_extensions.h

@@ -139,4 +139,36 @@ typedef struct _LV2_License_Interface {
    @}
 */
 
+/**
+   @defgroup plugin provided bypass
+
+	 A port with the designation "processing#enable" must
+	 control a plugin's internal bypass mode.
+
+	 If the port value is larger than zero the plugin processes
+	 normally.
+
+	 If the port value is zero, the plugin is expected to bypass
+	 all signals unmodified.
+
+	 The plugin is responsible for providing a click-free transition
+	 between the states.
+
+	 (values less than zero are reserved for future use:
+	 e.g click-free insert/removal of latent plugins.
+	 Generally values <= 0 are to be treated as bypassed.)
+
+   lv2:designation <http://ardour.org/lv2/processing#enable> ;
+
+   @{
+*/
+
+#define LV2_PROCESSING_URI "http://ardour.org/lv2/processing"
+#define LV2_PROCESSING_URI_PREFIX LV2_PROCESSING_URI "#"
+#define LV2_PROCESSING_URI__enable LV2_PROCESSING_URI_PREFIX "enable"
+
+/**
+   @}
+*/
+
 #endif

libs/ardour/ardour/lv2_plugin.h

@@ -126,6 +126,8 @@ class LIBARDOUR_API LV2Plugin : public ARDOUR::Plugin, public ARDOUR::Workee
 	bool parameter_is_output (uint32_t) const;
 	bool parameter_is_toggled (uint32_t) const;
 
+	uint32_t designated_bypass_port ();
+
 	boost::shared_ptr<ScalePoints>
 	get_scale_points(uint32_t port_index) const;
 

libs/ardour/lv2_plugin.cc

@@ -2703,6 +2703,22 @@ LV2Plugin::parameter_is_input(uint32_t param) const
 	return _port_flags[param] & PORT_INPUT;
 }
 
+uint32_t
+LV2Plugin::designated_bypass_port ()
+{
+#ifdef LV2_EXTENDED
+	const LilvPort* port = NULL;
+	LilvNode* designation = lilv_new_uri (_world.world, LV2_PROCESSING_URI__enable);
+	port = lilv_plugin_get_port_by_designation (
+			_impl->plugin, _world.lv2_InputPort, designation);
+	lilv_node_free(designation);
+	if (port) {
+		return lilv_port_get_index (_impl->plugin, port);
+	}
+#endif
+	return UINT32_MAX;
+}
+
 void
 LV2Plugin::print_parameter(uint32_t param, char* buf, uint32_t len) const
 {