6 files changed, 855 insertions, 0 deletions

diff --git a/plugins/eg-params.lv2/README.txt b/plugins/eg-params.lv2/README.txt
new file mode 100644
index 0000000..acf90c1
--- /dev/null
+++ b/plugins/eg-params.lv2/README.txt
@@ -0,0 +1,21 @@
+== Params ==
+
+The basic LV2 mechanism for controls is
+http://lv2plug.in/ns/lv2core#ControlPort[lv2:ControlPort], inherited from
+LADSPA.  Control ports are problematic because they are not sample accurate,
+support only one type (`float`), and require that plugins poll to know when a
+control has changed.
+
+Parameters can be used instead to address these issues.  Parameters can be
+thought of as properties of a plugin instance; they are identified by URI and
+have a value of any type.  This deliberately meshes with the concept of plugin
+state defined by the http://lv2plug.in/ns/ext/state[LV2 state extension].
+The state extension allows plugins to save and restore their parameters (along
+with other internal state information, if necessary).
+
+Parameters are accessed and manipulated using messages sent via a sequence
+port.  The http://lv2plug.in/ns/ext/patch[LV2 patch extension] defines the
+standard messages for working with parameters.  Typically, only two are used
+for simple plugins: http://lv2plug.in/ns/ext/patch#Set[patch:Set] sets a
+parameter to some value, and http://lv2plug.in/ns/ext/patch#Get[patch:Get]
+requests that the plugin send a description of its parameters.
diff --git a/plugins/eg-params.lv2/manifest.ttl.in b/plugins/eg-params.lv2/manifest.ttl.in
new file mode 100644
index 0000000..913de7c
--- /dev/null
+++ b/plugins/eg-params.lv2/manifest.ttl.in
@@ -0,0 +1,7 @@
+@prefix lv2:  <http://lv2plug.in/ns/lv2core#> .
+@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
+
+<http://lv2plug.in/plugins/eg-params>
+	a lv2:Plugin ;
+	lv2:binary <params@LIB_EXT@> ;
+	rdfs:seeAlso <params.ttl> .
diff --git a/plugins/eg-params.lv2/params.c b/plugins/eg-params.lv2/params.c
new file mode 100644
index 0000000..94d34a5
--- /dev/null
+++ b/plugins/eg-params.lv2/params.c
@@ -0,0 +1,526 @@
+/*
+  LV2 Parameter Example Plugin
+  Copyright 2014-2016 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include "state_map.h"
+
+#include "lv2/atom/atom.h"
+#include "lv2/atom/forge.h"
+#include "lv2/atom/util.h"
+#include "lv2/core/lv2.h"
+#include "lv2/core/lv2_util.h"
+#include "lv2/log/log.h"
+#include "lv2/log/logger.h"
+#include "lv2/midi/midi.h"
+#include "lv2/patch/patch.h"
+#include "lv2/state/state.h"
+#include "lv2/urid/urid.h"
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define MAX_STRING 1024
+
+#define EG_PARAMS_URI    "http://lv2plug.in/plugins/eg-params"
+
+#define N_PROPS 9
+
+typedef struct {
+	LV2_URID plugin;
+	LV2_URID atom_Path;
+	LV2_URID atom_Sequence;
+	LV2_URID atom_URID;
+	LV2_URID atom_eventTransfer;
+	LV2_URID eg_spring;
+	LV2_URID midi_Event;
+	LV2_URID patch_Get;
+	LV2_URID patch_Set;
+	LV2_URID patch_Put;
+	LV2_URID patch_body;
+	LV2_URID patch_subject;
+	LV2_URID patch_property;
+	LV2_URID patch_value;
+} URIs;
+
+typedef struct {
+	LV2_Atom_Int    aint;
+	LV2_Atom_Long   along;
+	LV2_Atom_Float  afloat;
+	LV2_Atom_Double adouble;
+	LV2_Atom_Bool   abool;
+	LV2_Atom        astring;
+	char            string[MAX_STRING];
+	LV2_Atom        apath;
+	char            path[MAX_STRING];
+	LV2_Atom_Float  lfo;
+	LV2_Atom_Float  spring;
+} State;
+
+static inline void
+map_uris(LV2_URID_Map* map, URIs* uris)
+{
+	uris->plugin             = map->map(map->handle, EG_PARAMS_URI);
+
+	uris->atom_Path          = map->map(map->handle, LV2_ATOM__Path);
+	uris->atom_Sequence      = map->map(map->handle, LV2_ATOM__Sequence);
+	uris->atom_URID          = map->map(map->handle, LV2_ATOM__URID);
+	uris->atom_eventTransfer = map->map(map->handle, LV2_ATOM__eventTransfer);
+	uris->eg_spring          = map->map(map->handle, EG_PARAMS_URI "#spring");
+	uris->midi_Event         = map->map(map->handle, LV2_MIDI__MidiEvent);
+	uris->patch_Get          = map->map(map->handle, LV2_PATCH__Get);
+	uris->patch_Set          = map->map(map->handle, LV2_PATCH__Set);
+	uris->patch_Put          = map->map(map->handle, LV2_PATCH__Put);
+	uris->patch_body         = map->map(map->handle, LV2_PATCH__body);
+	uris->patch_subject      = map->map(map->handle, LV2_PATCH__subject);
+	uris->patch_property     = map->map(map->handle, LV2_PATCH__property);
+	uris->patch_value        = map->map(map->handle, LV2_PATCH__value);
+}
+
+enum {
+	PARAMS_IN  = 0,
+	PARAMS_OUT = 1
+};
+
+typedef struct {
+	// Features
+	LV2_URID_Map*   map;
+	LV2_URID_Unmap* unmap;
+	LV2_Log_Logger  log;
+
+	// Forge for creating atoms
+	LV2_Atom_Forge forge;
+
+	// Ports
+	const LV2_Atom_Sequence* in_port;
+	LV2_Atom_Sequence*       out_port;
+
+	// URIs
+	URIs uris;
+
+	// Plugin state
+	StateMapItem props[N_PROPS];
+	State        state;
+
+	// Buffer for making strings from URIDs if unmap is not provided
+	char urid_buf[12];
+} Params;
+
+static void
+connect_port(LV2_Handle instance,
+             uint32_t   port,
+             void*      data)
+{
+	Params* self = (Params*)instance;
+	switch (port) {
+	case PARAMS_IN:
+		self->in_port = (const LV2_Atom_Sequence*)data;
+		break;
+	case PARAMS_OUT:
+		self->out_port = (LV2_Atom_Sequence*)data;
+		break;
+	default:
+		break;
+	}
+}
+
+static LV2_Handle
+instantiate(const LV2_Descriptor*     descriptor,
+            double                    rate,
+            const char*               path,
+            const LV2_Feature* const* features)
+{
+	// Allocate instance
+	Params* self = (Params*)calloc(1, sizeof(Params));
+	if (!self) {
+		return NULL;
+	}
+
+	// Get host features
+	const char* missing = lv2_features_query(
+		features,
+		LV2_LOG__log,    &self->log.log, false,
+		LV2_URID__map,   &self->map,     true,
+		LV2_URID__unmap, &self->unmap,   false,
+		NULL);
+	lv2_log_logger_set_map(&self->log, self->map);
+	if (missing) {
+		lv2_log_error(&self->log, "Missing feature <%s>\n", missing);
+		free(self);
+		return NULL;
+	}
+
+	// Map URIs and initialise forge
+	map_uris(self->map, &self->uris);
+	lv2_atom_forge_init(&self->forge, self->map);
+
+	// Initialise state dictionary
+	State* state = &self->state;
+	state_map_init(
+		self->props, self->map, self->map->handle,
+		EG_PARAMS_URI "#int",    STATE_MAP_INIT(Int,    &state->aint),
+		EG_PARAMS_URI "#long",   STATE_MAP_INIT(Long,   &state->along),
+		EG_PARAMS_URI "#float",  STATE_MAP_INIT(Float,  &state->afloat),
+		EG_PARAMS_URI "#double", STATE_MAP_INIT(Double, &state->adouble),
+		EG_PARAMS_URI "#bool",   STATE_MAP_INIT(Bool,   &state->abool),
+		EG_PARAMS_URI "#string", STATE_MAP_INIT(String, &state->astring),
+		EG_PARAMS_URI "#path",   STATE_MAP_INIT(Path,   &state->apath),
+		EG_PARAMS_URI "#lfo",    STATE_MAP_INIT(Float,  &state->lfo),
+		EG_PARAMS_URI "#spring", STATE_MAP_INIT(Float,  &state->spring),
+		NULL);
+
+	return (LV2_Handle)self;
+}
+
+static void
+cleanup(LV2_Handle instance)
+{
+	free(instance);
+}
+
+/** Helper function to unmap a URID if possible. */
+static const char*
+unmap(Params* self, LV2_URID urid)
+{
+	if (self->unmap) {
+		return self->unmap->unmap(self->unmap->handle, urid);
+	} else {
+		snprintf(self->urid_buf, sizeof(self->urid_buf), "%u", urid);
+		return self->urid_buf;
+	}
+}
+
+static LV2_State_Status
+check_type(Params*  self,
+           LV2_URID key,
+           LV2_URID type,
+           LV2_URID required_type)
+{
+	if (type != required_type) {
+		lv2_log_trace(
+			&self->log, "Bad type <%s> for <%s> (needs <%s>)\n",
+			unmap(self, type),
+			unmap(self, key),
+			unmap(self, required_type));
+		return LV2_STATE_ERR_BAD_TYPE;
+	}
+	return LV2_STATE_SUCCESS;
+}
+
+static LV2_State_Status
+set_parameter(Params*     self,
+              LV2_URID    key,
+              uint32_t    size,
+              LV2_URID    type,
+              const void* body,
+              bool        from_state)
+{
+	// Look up property in state dictionary
+	const StateMapItem* entry = state_map_find(self->props, N_PROPS, key);
+	if (!entry) {
+		lv2_log_trace(&self->log, "Unknown parameter <%s>\n", unmap(self, key));
+		return LV2_STATE_ERR_NO_PROPERTY;
+	}
+
+	// Ensure given type matches property's type
+	if (check_type(self, key, type, entry->value->type)) {
+		return LV2_STATE_ERR_BAD_TYPE;
+	}
+
+	// Set property value in state dictionary
+	lv2_log_trace(&self->log, "Set <%s>\n", entry->uri);
+	memcpy(entry->value + 1, body, size);
+	entry->value->size = size;
+	return LV2_STATE_SUCCESS;
+}
+
+static const LV2_Atom*
+get_parameter(Params* self, LV2_URID key)
+{
+	const StateMapItem* entry = state_map_find(self->props, N_PROPS, key);
+	if (entry) {
+		lv2_log_trace(&self->log, "Get <%s>\n", entry->uri);
+		return entry->value;
+	}
+
+	lv2_log_trace(&self->log, "Unknown parameter <%s>\n", unmap(self, key));
+	return NULL;
+}
+
+static LV2_State_Status
+write_param_to_forge(LV2_State_Handle handle,
+                     uint32_t         key,
+                     const void*      value,
+                     size_t           size,
+                     uint32_t         type,
+                     uint32_t         flags)
+{
+	LV2_Atom_Forge* forge = (LV2_Atom_Forge*)handle;
+
+	if (!lv2_atom_forge_key(forge, key) ||
+	    !lv2_atom_forge_atom(forge, size, type) ||
+	    !lv2_atom_forge_write(forge, value, size)) {
+		return LV2_STATE_ERR_UNKNOWN;
+	}
+
+	return LV2_STATE_SUCCESS;
+}
+
+static void
+store_prop(Params*                  self,
+           LV2_State_Map_Path*      map_path,
+           LV2_State_Status*        save_status,
+           LV2_State_Store_Function store,
+           LV2_State_Handle         handle,
+           LV2_URID                 key,
+           const LV2_Atom*          value)
+{
+	LV2_State_Status st;
+	if (map_path && value->type == self->uris.atom_Path) {
+		// Map path to abstract path for portable storage
+		const char* path  = (const char*)(value + 1);
+		char*       apath = map_path->abstract_path(map_path->handle, path);
+		st = store(handle,
+		           key,
+		           apath,
+		           strlen(apath) + 1,
+		           self->uris.atom_Path,
+		           LV2_STATE_IS_POD | LV2_STATE_IS_PORTABLE);
+		free(apath);
+	} else {
+		// Store simple property
+		st = store(handle,
+		           key,
+		           value + 1,
+		           value->size,
+		           value->type,
+		           LV2_STATE_IS_POD | LV2_STATE_IS_PORTABLE);
+	}
+
+	if (save_status && !*save_status) {
+		*save_status = st;
+	}
+}
+
+/**
+   State save method.
+
+   This is used in the usual way when called by the host to save plugin state,
+   but also internally for writing messages in the audio thread by passing a
+   "store" function which actually writes the description to the forge.
+*/
+static LV2_State_Status
+save(LV2_Handle                instance,
+     LV2_State_Store_Function  store,
+     LV2_State_Handle          handle,
+     uint32_t                  flags,
+     const LV2_Feature* const* features)
+{
+	Params*             self     = (Params*)instance;
+	LV2_State_Map_Path* map_path = (LV2_State_Map_Path*)lv2_features_data(
+		features, LV2_STATE__mapPath);
+
+	LV2_State_Status st = LV2_STATE_SUCCESS;
+	for (unsigned i = 0; i < N_PROPS; ++i) {
+		StateMapItem* prop = &self->props[i];
+		store_prop(self, map_path, &st, store, handle, prop->urid, prop->value);
+	}
+
+	return st;
+}
+
+static void
+retrieve_prop(Params*                     self,
+              LV2_State_Status*           restore_status,
+              LV2_State_Retrieve_Function retrieve,
+              LV2_State_Handle            handle,
+              LV2_URID                    key)
+{
+	// Retrieve value from saved state
+	size_t      vsize;
+	uint32_t    vtype;
+	uint32_t    vflags;
+	const void* value = retrieve(handle, key, &vsize, &vtype, &vflags);
+
+	// Set plugin instance state
+	const LV2_State_Status st = value
+		? set_parameter(self, key, vsize, vtype, value, true)
+		: LV2_STATE_ERR_NO_PROPERTY;
+
+	if (!*restore_status) {
+		*restore_status = st;  // Set status if there has been no error yet
+	}
+}
+
+/** State restore method. */
+static LV2_State_Status
+restore(LV2_Handle                  instance,
+        LV2_State_Retrieve_Function retrieve,
+        LV2_State_Handle            handle,
+        uint32_t                    flags,
+        const LV2_Feature* const*   features)
+{
+	Params*          self = (Params*)instance;
+	LV2_State_Status st   = LV2_STATE_SUCCESS;
+
+	for (unsigned i = 0; i < N_PROPS; ++i) {
+		retrieve_prop(self, &st, retrieve, handle, self->props[i].urid);
+	}
+
+	return st;
+}
+
+static inline bool
+subject_is_plugin(Params* self, const LV2_Atom_URID* subject)
+{
+	// This simple plugin only supports one subject: itself
+	return (!subject || (subject->atom.type == self->uris.atom_URID &&
+	                     subject->body      == self->uris.plugin));
+}
+
+static void
+run(LV2_Handle instance, uint32_t sample_count)
+{
+	Params* self = (Params*)instance;
+	URIs*   uris = &self->uris;
+
+	// Initially, self->out_port contains a Chunk with size set to capacity
+	// Set up forge to write directly to output port
+	const uint32_t out_capacity = self->out_port->atom.size;
+	lv2_atom_forge_set_buffer(&self->forge,
+	                          (uint8_t*)self->out_port,
+	                          out_capacity);
+
+	// Start a sequence in the output port
+	LV2_Atom_Forge_Frame out_frame;
+	lv2_atom_forge_sequence_head(&self->forge, &out_frame, 0);
+
+	// Read incoming events
+	LV2_ATOM_SEQUENCE_FOREACH(self->in_port, ev) {
+		const LV2_Atom_Object* obj = (const LV2_Atom_Object*)&ev->body;
+		if (obj->body.otype == uris->patch_Set) {
+			// Get the property and value of the set message
+			const LV2_Atom_URID* subject  = NULL;
+			const LV2_Atom_URID* property = NULL;
+			const LV2_Atom*      value    = NULL;
+			lv2_atom_object_get(obj,
+			                    uris->patch_subject,  (const LV2_Atom**)&subject,
+			                    uris->patch_property, (const LV2_Atom**)&property,
+			                    uris->patch_value,    &value,
+			                    0);
+			if (!subject_is_plugin(self, subject)) {
+				lv2_log_error(&self->log, "Set for unknown subject\n");
+			} else if (!property) {
+				lv2_log_error(&self->log, "Set with no property\n");
+			} else if (property->atom.type != uris->atom_URID) {
+				lv2_log_error(&self->log, "Set property is not a URID\n");
+			} else {
+				// Set property to the given value
+				const LV2_URID key = property->body;
+				set_parameter(self, key, value->size, value->type, value + 1, false);
+			}
+		} else if (obj->body.otype == uris->patch_Get) {
+			// Get the property of the get message
+			const LV2_Atom_URID* subject  = NULL;
+			const LV2_Atom_URID* property = NULL;
+			lv2_atom_object_get(obj,
+			                    uris->patch_subject,  (const LV2_Atom**)&subject,
+			                    uris->patch_property, (const LV2_Atom**)&property,
+			                    0);
+			if (!subject_is_plugin(self, subject)) {
+				lv2_log_error(&self->log, "Get with unknown subject\n");
+			} else if (!property) {
+				// Get with no property, emit complete state
+				lv2_atom_forge_frame_time(&self->forge, ev->time.frames);
+				LV2_Atom_Forge_Frame pframe;
+				lv2_atom_forge_object(&self->forge, &pframe, 0, uris->patch_Put);
+				lv2_atom_forge_key(&self->forge, uris->patch_body);
+
+				LV2_Atom_Forge_Frame bframe;
+				lv2_atom_forge_object(&self->forge, &bframe, 0, 0);
+				save(self, write_param_to_forge, &self->forge, 0, NULL);
+
+				lv2_atom_forge_pop(&self->forge, &bframe);
+				lv2_atom_forge_pop(&self->forge, &pframe);
+			} else if (property->atom.type != uris->atom_URID) {
+				lv2_log_error(&self->log, "Get property is not a URID\n");
+			} else {
+				// Get for a specific property
+				const LV2_URID  key   = property->body;
+				const LV2_Atom* value = get_parameter(self, key);
+				if (value) {
+					lv2_atom_forge_frame_time(&self->forge, ev->time.frames);
+					LV2_Atom_Forge_Frame frame;
+					lv2_atom_forge_object(&self->forge, &frame, 0, uris->patch_Set);
+					lv2_atom_forge_key(&self->forge, uris->patch_property);
+					lv2_atom_forge_urid(&self->forge, property->body);
+					store_prop(self, NULL, NULL, write_param_to_forge, &self->forge,
+					           uris->patch_value, value);
+					lv2_atom_forge_pop(&self->forge, &frame);
+				}
+			}
+		} else {
+			lv2_log_trace(&self->log, "Unknown object type <%s>\n",
+			              unmap(self, obj->body.otype));
+		}
+	}
+
+	if (self->state.spring.body > 0.0f) {
+		const float spring = self->state.spring.body;
+		self->state.spring.body = (spring >= 0.001) ? spring - 0.001 : 0.0;
+		lv2_atom_forge_frame_time(&self->forge, 0);
+		LV2_Atom_Forge_Frame frame;
+		lv2_atom_forge_object(&self->forge, &frame, 0, uris->patch_Set);
+
+		lv2_atom_forge_key(&self->forge, uris->patch_property);
+		lv2_atom_forge_urid(&self->forge, uris->eg_spring);
+		lv2_atom_forge_key(&self->forge, uris->patch_value);
+		lv2_atom_forge_float(&self->forge, self->state.spring.body);
+
+		lv2_atom_forge_pop(&self->forge, &frame);
+	}
+
+	lv2_atom_forge_pop(&self->forge, &out_frame);
+}
+
+static const void*
+extension_data(const char* uri)
+{
+	static const LV2_State_Interface state = { save, restore };
+	if (!strcmp(uri, LV2_STATE__interface)) {
+		return &state;
+	}
+	return NULL;
+}
+
+static const LV2_Descriptor descriptor = {
+	EG_PARAMS_URI,
+	instantiate,
+	connect_port,
+	NULL,  // activate,
+	run,
+	NULL,  // deactivate,
+	cleanup,
+	extension_data
+};
+
+LV2_SYMBOL_EXPORT const LV2_Descriptor*
+lv2_descriptor(uint32_t index)
+{
+	return (index == 0) ? &descriptor : NULL;
+}
diff --git a/plugins/eg-params.lv2/params.ttl b/plugins/eg-params.lv2/params.ttl
new file mode 100644
index 0000000..dbcf6aa
--- /dev/null
+++ b/plugins/eg-params.lv2/params.ttl
@@ -0,0 +1,126 @@
+@prefix atom: <http://lv2plug.in/ns/ext/atom#> .
+@prefix doap: <http://usefulinc.com/ns/doap#> .
+@prefix lv2: <http://lv2plug.in/ns/lv2core#> .
+@prefix param: <http://lv2plug.in/ns/ext/parameters#> .
+@prefix patch: <http://lv2plug.in/ns/ext/patch#> .
+@prefix plug: <http://lv2plug.in/plugins/eg-params#> .
+@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
+@prefix state: <http://lv2plug.in/ns/ext/state#> .
+@prefix urid: <http://lv2plug.in/ns/ext/urid#> .
+@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
+
+# An existing parameter or RDF property can be used as a parameter.  The LV2
+# parameters extension <http://lv2plug.in/ns/ext/parameters> defines many
+# common audio parameters.  Where possible, existing parameters should be used
+# so hosts can intelligently control plugins.
+
+# If no suitable parameter exists, one can be defined for the plugin like so:
+
+plug:int
+	a lv2:Parameter ;
+	rdfs:label "int" ;
+	rdfs:range atom:Int .
+
+plug:long
+	a lv2:Parameter ;
+	rdfs:label "long" ;
+	rdfs:range atom:Long .
+
+plug:float
+	a lv2:Parameter ;
+	rdfs:label "float" ;
+	rdfs:range atom:Float .
+
+plug:double
+	a lv2:Parameter ;
+	rdfs:label "double" ;
+	rdfs:range atom:Double .
+
+plug:bool
+	a lv2:Parameter ;
+	rdfs:label "bool" ;
+	rdfs:range atom:Bool .
+
+plug:string
+	a lv2:Parameter ;
+	rdfs:label "string" ;
+	rdfs:range atom:String .
+
+plug:path
+	a lv2:Parameter ;
+	rdfs:label "path" ;
+	rdfs:range atom:Path .
+
+plug:lfo
+	a lv2:Parameter ;
+	rdfs:label "LFO" ;
+	rdfs:range atom:Float ;
+	lv2:minimum -1.0 ;
+	lv2:maximum 1.0 .
+
+plug:spring
+	a lv2:Parameter ;
+	rdfs:label "spring" ;
+	rdfs:range atom:Float .
+
+# Most of the plugin description is similar to the others we have seen, but
+# this plugin has only two ports, for receiving and sending messages used to
+# manipulate and access parameters.
+<http://lv2plug.in/plugins/eg-params>
+	a lv2:Plugin ,
+		lv2:UtilityPlugin ;
+	doap:name "Example Parameters" ;
+	doap:license <http://opensource.org/licenses/isc> ;
+	lv2:project <http://lv2plug.in/ns/lv2> ;
+	lv2:requiredFeature urid:map ;
+	lv2:optionalFeature lv2:hardRTCapable ,
+		state:loadDefaultState ;
+	lv2:extensionData state:interface ;
+	lv2:port [
+		a lv2:InputPort ,
+			atom:AtomPort ;
+		atom:bufferType atom:Sequence ;
+		atom:supports patch:Message ;
+		lv2:designation lv2:control ;
+		lv2:index 0 ;
+		lv2:symbol "in" ;
+		lv2:name "In"
+	] , [
+		a lv2:OutputPort ,
+			atom:AtomPort ;
+		atom:bufferType atom:Sequence ;
+		atom:supports patch:Message ;
+		lv2:designation lv2:control ;
+		lv2:index 1 ;
+		lv2:symbol "out" ;
+		lv2:name "Out"
+	] ;
+# The plugin must list all parameters that can be written (e.g. changed by the
+# user) as patch:writable:
+	patch:writable plug:int ,
+		plug:long ,
+		plug:float ,
+		plug:double ,
+		plug:bool ,
+		plug:string ,
+		plug:path ,
+		plug:spring ;
+# Similarly, parameters that may change internally must be listed as patch:readable,
+# meaning to host should watch for changes to the parameter's value:
+		patch:readable plug:lfo ,
+			plug:spring ;
+# Parameters map directly to properties of the plugin's state.  So, we can
+# specify initial parameter values with the state:state property.  The
+# state:loadDefaultState feature (required above) requires that the host loads
+# the default state after instantiation but before running the plugin.
+	state:state [
+		plug:int 0 ;
+		plug:long "0"^^xsd:long ;
+		plug:float 0.1234 ;
+		plug:double "0e0"^^xsd:double ;
+		plug:bool false ;
+		plug:string "Hello, world" ;
+		plug:path <params.ttl> ;
+		plug:spring 0.0 ;
+		plug:lfo 0.0
+	] .
diff --git a/plugins/eg-params.lv2/state_map.h b/plugins/eg-params.lv2/state_map.h
new file mode 100644
index 0000000..c80d4a2
--- /dev/null
+++ b/plugins/eg-params.lv2/state_map.h
@@ -0,0 +1,114 @@
+/*
+  LV2 State Map
+  Copyright 2016 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include "lv2/atom/atom.h"
+#include "lv2/urid/urid.h"
+
+#include <stdarg.h>
+#include <stdlib.h>
+
+/** Entry in an array that serves as a dictionary of properties. */
+typedef struct {
+	const char* uri;
+	LV2_URID    urid;
+	LV2_Atom*   value;
+} StateMapItem;
+
+/** Comparator for StateMapItems sorted by URID. */
+static int
+state_map_cmp(const void* a, const void* b)
+{
+	const StateMapItem* ka = (const StateMapItem*)a;
+	const StateMapItem* kb = (const StateMapItem*)b;
+	if (ka->urid < kb->urid) {
+		return -1;
+	} else if (kb->urid < ka->urid) {
+		return 1;
+	}
+	return 0;
+}
+
+/** Helper macro for terse state map initialisation. */
+#define STATE_MAP_INIT(type, ptr) \
+	(LV2_ATOM__ ## type), \
+	(sizeof(*ptr) - sizeof(LV2_Atom)), \
+	(ptr)
+
+/**
+   Initialise a state map.
+
+   The variable parameters list must be NULL terminated, and is a sequence of
+   const char* uri, const char* type, uint32_t size, LV2_Atom* value.  The
+   value must point to a valid atom that resides elsewhere, the state map is
+   only an index and does not contain actual state values.  The macro
+   STATE_MAP_INIT can be used to make simpler code when state is composed of
+   standard atom types, for example:
+
+   struct Plugin {
+       LV2_URID_Map* map;
+       StateMapItem  props[3];
+       // ...
+   };
+
+   state_map_init(
+       self->props, self->map, self->map->handle,
+       PLUG_URI "#gain",   STATE_MAP_INIT(Float,  &state->gain),
+       PLUG_URI "#offset", STATE_MAP_INIT(Int,    &state->offset),
+       PLUG_URI "#file",   STATE_MAP_INIT(Path,   &state->file),
+       NULL);
+*/
+static void
+state_map_init(StateMapItem        dict[],
+               LV2_URID_Map*       map,
+               LV2_URID_Map_Handle handle,
+               /* const char* uri, const char* type, uint32_t size, LV2_Atom* value */ ...)
+{
+	// Set dict entries from parameters
+	unsigned i = 0;
+	va_list  args;
+	va_start(args, handle);
+	for (const char* uri; (uri = va_arg(args, const char*)); ++i) {
+		const char*     type  = va_arg(args, const char*);
+		const uint32_t  size  = va_arg(args, uint32_t);
+		LV2_Atom* const value = va_arg(args, LV2_Atom*);
+		dict[i].uri         = uri;
+		dict[i].urid        = map->map(map->handle, uri);
+		dict[i].value       = value;
+		dict[i].value->size = size;
+		dict[i].value->type = map->map(map->handle, type);
+	}
+	va_end(args);
+
+	// Sort for fast lookup by URID by state_map_find()
+	qsort(dict, i, sizeof(StateMapItem), state_map_cmp);
+}
+
+/**
+   Retrieve an item from a state map by URID.
+
+   This takes O(lg(n)) time, and is useful for implementing generic property
+   access with little code, for example to respond to patch:Get messages for a
+   specific property.
+*/
+static StateMapItem*
+state_map_find(StateMapItem dict[], uint32_t n_entries, LV2_URID urid)
+{
+	const StateMapItem key = { NULL, urid, NULL };
+	return (StateMapItem*)bsearch(
+		&key, dict, n_entries, sizeof(StateMapItem), state_map_cmp);
+}
+
diff --git a/plugins/eg-params.lv2/wscript b/plugins/eg-params.lv2/wscript
new file mode 100644
index 0000000..f618898
--- /dev/null
+++ b/plugins/eg-params.lv2/wscript
@@ -0,0 +1,61 @@
+#!/usr/bin/env python
+from waflib.extras import autowaf as autowaf
+import re
+
+# Variables for 'waf dist'
+APPNAME = 'eg-params.lv2'
+VERSION = '1.0.0'
+
+# Mandatory variables
+top = '.'
+out = 'build'
+
+def options(opt):
+    opt.load('compiler_c')
+    opt.load('lv2')
+    autowaf.set_options(opt)
+
+def configure(conf):
+    conf.load('compiler_c', cache=True)
+    conf.load('lv2', cache=True)
+    conf.load('autowaf', cache=True)
+
+    if not autowaf.is_child():
+        autowaf.check_pkg(conf, 'lv2', atleast_version='1.12.1', uselib_store='LV2')
+
+def build(bld):
+    bundle = 'eg-params.lv2'
+
+    # Make a pattern for shared objects without the 'lib' prefix
+    module_pat = re.sub('^lib', '', bld.env.cshlib_PATTERN)
+    module_ext = module_pat[module_pat.rfind('.'):]
+
+    # Build manifest.ttl by substitution (for portable lib extension)
+    bld(features     = 'subst',
+        source       = 'manifest.ttl.in',
+        target       = '%s/%s' % (bundle, 'manifest.ttl'),
+        install_path = '${LV2DIR}/%s' % bundle,
+        LIB_EXT      = module_ext)
+
+    # Copy other data files to build bundle (build/eg-params.lv2)
+    for i in ['params.ttl']:
+        bld(features     = 'subst',
+            is_copy      = True,
+            source       = i,
+            target       = '%s/%s' % (bundle, i),
+            install_path = '${LV2DIR}/%s' % bundle)
+
+    # Use LV2 headers from parent directory if building as a sub-project
+    includes = ['.']
+    if autowaf.is_child:
+        includes += ['../..']
+
+    # Build plugin library
+    obj = bld(features     = 'c cshlib',
+              source       = 'params.c',
+              name         = 'params',
+              target       = '%s/params' % bundle,
+              install_path = '${LV2DIR}/%s' % bundle,
+              use          = 'LV2',
+              includes     = includes)
+    obj.env.cshlib_PATTERN = module_pat