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-# LV2 State Extension
-# Copyright 2010-2011 David Robillard <d@drobilla.net>
-# Copyright 2010 Leonard Ritter <paniq@paniq.org>
-#
-# 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.
-
-@prefix state: <http://lv2plug.in/ns/ext/state#> .
-@prefix doap: <http://usefulinc.com/ns/doap#> .
-@prefix foaf: <http://xmlns.com/foaf/0.1/> .
-@prefix lv2: <http://lv2plug.in/ns/lv2core#> .
-@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
-@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
-
-<http://lv2plug.in/ns/ext/state>
- a lv2:Specification ;
- doap:name "LV2 State" ;
- doap:shortdesc "An interface for LV2 plugins to save and restore state." ;
- doap:license <http://opensource.org/licenses/isc-license> ;
- doap:release [
- doap:revision "0.2" ;
- doap:created "2011-11-14"
- ] ;
- doap:developer [
- a foaf:Person ;
- foaf:name "Leonard Ritter" ;
- foaf:homepage <http://paniq.org> ;
- ] ;
- doap:maintainer [
- a foaf:Person ;
- foaf:name "David Robillard" ;
- foaf:homepage <http://drobilla.net/> ;
- rdfs:seeAlso <http://drobilla.net/drobilla.rdf>
- ] ;
- lv2:documentation """
-<p>This extension provides a mechanism for plugins to save and restore state
-across instances, allowing hosts to save, restore, clone, or take a snapshot of
-a plugin instance's state at any point in time. The intention is for a plugin
-instance's state to be <em>completely</em> described by port values (as with all
-LV2 plugins) and a simple dictionary.</p>
-
-<p>The <q>state</q> described by this extension is conceptually a single
-key/value dictionary, where keys are URIDs and values are type-tagged blobs of
-any type. The plugin provides an LV2_State_Interface for working with this
-state. To save or restore, the host calls LV2_State_Interface::save() or
-LV2_State_Interface::restore(), passing a callback to be used for handling a
-single key/value pair. The host is free to implement saving and restoring in
-any way; the actual mechanism is completely abstract from the plugin's
-perspective.</p>
-
-<p>Because state is a simple dictionary, hosts and plugins can work with it
-easily from many languages and protocols. Keys are URIDs for performance
-reasons as well as RDF compatibility, which makes it simple to serialise state
-in many formats (e.g. any RDF syntax, JSON, XML, key/value databases such as
-BDB, etc.). In particular, state can be elegantly described in a plugin's
-Turtle description, which is useful for e.g. presets or default state.
-Specific keys may be described in Turtle on the fly or in extensions,
-allowing plugins to use common well-defined keys.</p>
-
-<p>This extension defines a conceptual model of state and a mechanism for
-saving and restoring it, but no interface for manipulating it dynamically.
-While no such mechanism is defined here, dynamic control of plugins SHOULD be
-achieved by generic manipulations of the same conceptual state dictionary used
-by this extension (e.g. <code>plugin->set(key, value)</code>). Accordingly,
-plugins SHOULD use meaningful and well-defined keys wherever possible.</p>
-
-<p>In pseudo code, a typical use case in a plugin is:</p>
-<pre class="c-code">
-#define NS_EG "http://example.org/"
-#define NS_ATOM "http://lv2plug.in/ns/ext/atom#"
-
-LV2_Handle my_instantiate(...)
-{
- MyPlugin* plugin = ...;
- plugin->uris.atom_String = map_uri(NS_ATOM "String");
- plugin->uris.eg_greeting = map_uri(NS_EG "greeting");
- plugin->state.greeting = strdup("Hello");
- return plugin;
-}
-
-void my_save(LV2_Handle instance,
- LV2_State_Store_Function store,
- void* handle,
- uint32_t flags,
- const LV2_Feature *const * features)
-
-{
- MyPlugin* plugin = (MyPlugin*)instance;
- const char* greeting = plugin->state.greeting;
-
- store(handle,
- plugin->uris.eg_greeting,
- greeting,
- strlen(greeting) + 1,
- plugin->uris.atom_String,
- LV2_STATE_IS_POD | LV2_STATE_IS_PORTABLE);
-}
-
-void my_restore(LV2_Handle instance,
- LV2_State_Retrieve_Function retrieve,
- void* handle,
- uint32_t flags,
- const LV2_Feature *const * features)
-{
- MyPlugin* plugin = (MyPlugin*)instance;
-
- size_t size;
- uint32_t type;
- uint32_t flags;
- const char* greeting = retrieve(handle,
- plugin->uris.eg_greeting,
- &amp;size,
- &amp;type,
- &amp;flags);
-
- if (greeting) {
- free(plugin->state->greeting);
- plugin->state->greeting = strdup(greeting);
- } else {
- plugin->state->greeting = strdup("Hello");
- }
-}
-
-const void* my_extension_data(const char* uri)
-{
- static const LV2_State_Interface state_iface = { my_save, my_restore };
- if (!strcmp(uri, LV2_STATE_INTERFACE_URI)) {
- return &amp;state_iface;
- }
-}
-</pre>
-
-<p>Similarly, a typical use case in a host is:</p>
-<pre class="c-code">
-int store_callback(void* handle,
- uint32_t key,
- const void* value,
- size_t size,
- uint32_t type,
- uint32_t flags)
-{
- if ((flags &amp; LV2_STATE_IS_POD)) {
- /* We only care about POD since we're keeping state in memory only.
- If this was for disk or network storage/transmission,
- LV2_STATE_IS_PORTABLE would have to be checked as well.
- */
- Map* state_map = (Map*)handle;
- state_map->insert(key, Value(copy(value), size, type, pod));
- return 0;
- } else {
- return 1; /* Non-POD events are unsupported. */
- }
-}
-
-Map get_plugin_state(LV2_Handle instance)
-{
- LV2_State* state = instance.extension_data("http://lv2plug.in/ns/ext/state");
- Map state_map;
- /** Request a fast/native/POD save, since we're just copying in memory */
- state.save(instance, store_callback, &amp;state_map,
- LV2_STATE_IS_POD|LV2_STATE_IS_NATIVE);
- return state_map;
-}
-</pre>
-""" .
-
-state:Interface
- a rdfs:Class ;
- rdfs:subClassOf lv2:ExtensionData ;
- lv2:documentation """
-<p>A structure (LV2_State_Interface) which contains functions to be called by
-the host to save and restore state. In order to support this extension, the
-plugin must return a valid LV2_State_Interface from
-LV2_Descriptor::extension_data() when it is called with
-LV2_STATE_INTERFACE_URI.</p>
-
-<p>The plugin data file should describe this like so:</p>
-<pre class="turtle-code">
-@prefix state: &lt;http://lv2plug.in/ns/ext/state#&gt; .
-
-&lt;plugin&gt;
- a lv2:Plugin ;
- lv2:extensionData state:Interface .
-</pre>
-""" .
-
-state:InstanceState
- a rdfs:Class ;
- rdfs:label "Plugin Instance State" ;
- rdfs:comment """
-This class is used to express a plugin instance's state in RDF. The key/value
-properties of the instance form the predicate/object (respectively) of triples
-with a state:InstanceState as the subject (see state:instanceState for an
-example). This may be used wherever it is useful to express a plugin instance's
-state in RDF (e.g. for serialisation, storing in a model, or transmitting over
-a network). Note that this class is provided because it may be useful for
-hosts, plugins, or extensions that work with instance state, but its use is not
-required to support the LV2 State extension.
-""" .
-
-state:instanceState
- a rdf:Property ;
- rdfs:range state:InstanceState ;
- lv2:documentation """
-<p>Predicate to relate a plugin instance to an InstanceState. This may be used
-wherever the state of a particular plugin instance needs to be represented.
-Note that the domain of this property is unspecified, since LV2 does not define
-any RDF class for plugin instance. This predicate may be used wherever it makes
-sense to do so, e.g.:</p>
-<pre class="turtle-code">
-@prefix eg: &lt;http://example.org/&gt; .
-
-&lt;plugininstance&gt; state:instanceState [
- eg:somekey "some value" ;
- eg:someotherkey "some other value" ;
- eg:favourite-number 2
-] .
-</pre>
-<p>Note that this property is provided because it may be useful for hosts,
-plugins, or extensions that work with instance state, but its use is not
-required to support the LV2 State extension.</p>
-""" .