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-# LV2 State Extension
-# Copyright 2010-2012 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 dcs: <http://ontologi.es/doap-changeset#> .
-@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#> .
-@prefix state: <http://lv2plug.in/ns/ext/state#> .
-
-<http://drobilla.net/drobilla#me>
- a foaf:Person ;
- foaf:name "David Robillard" ;
- foaf:homepage <http://drobilla.net/> ;
- foaf:mbox <mailto:d@drobilla.net> ;
- rdfs:seeAlso <http://drobilla.net/drobilla> .
-
-<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> ;
- doap:release [
- doap:revision "0.5" ;
- doap:created "2012-01-29" ;
- dcs:blame <http://drobilla.net/drobilla#me>
- ] ;
- 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 simple mechanism for plugins to save and restore
-state across instances, allowing hosts to save and restore a plugin instance's
-state at any time. The goal is for an instance's state to be
-<em>completely</em> described by port values (as with all LV2 plugins) and a
-dictionary.</p>
-
-<p>The <q>state</q> described by this extension is conceptually a simple
-key:value dictionary, where keys are URIDs (URIs mapped to integers) and values
-are type-tagged blobs of any type. A single key:value pair is called a
-<q>property</q>. To implement state, the plugin provides a state:Interface to
-the host. 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 property. The host is free to implement property storage and retrieval
-in any way.</p>
-
-<p>This state model is simple yet has many benefits:</p>
-<ul>
- <li>URID keys provide both fast performance and RDF compatibility.</li>
- <li>Fully extensible, no limitations on keys or value types.</li>
- <li>Easy to serialise in many formats (e.g. any RDF syntax, plain
- text, JSON, XML, key:value databases, SQL, s-expressions, etc.).</li>
- <li>Elegantly described in Turtle, which is useful for describing presets
- or default state in LV2 data files (the predicate state:state is provided
- for this purpose).</li>
- <li>Does not impose any file formats, data structures, or file system
- requirements.</li>
- <li>Suitable for portable persistent state as well as fast in-memory
- snapshots.</li>
- <li>Easily stored in a typical <q>map</q> or <q>dictionary</q> data
- structure.</li>
- <li>Keys may be defined by extensions and used by several plugins,
- making state meaningful enabling dynamic state control.</li>
-</ul>
-
-<p>Implementations or further extensions which work with plugin state
-(including dynamic plugin control) SHOULD work entirely within this model.
-That is, <strong>do not complicate the state model</strong>. <em>All</em>
-information required to express an instance's state at any given time can, and
-should, be expressed within this model.</p>
-
-<h3>Plugin Code Example</h3>
-
-<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>
-
-<h3>Host Code Example</h3>
-
-<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>
-
-<h3>Referring to Existing Files</h3>
-
-<p>Plugins may need to refer to files (e.g. loaded samples) in their state.
-This is done by storing the file's path as a property just like any other
-value. However, there are some rules which MUST be followed when storing
-paths, see <a href="#mapPath">state:mapPath</a> for details.</p>
-
-<h3>Creating New Files or Directories</h3>
-
-<p>Implementations are strongly encouraged to avoid the use of files and simply
-store all state as properties whenever possible. However, occasionally the
-ability to create files is necessary. The feature <a
-href="#newPath">state:newPath</a> makes this possible, if it is provided by the
-host.</p>
-""" .
-
-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:State
- a rdfs:Class ;
- rdfs:label "Plugin Instance State" ;
- lv2:documentation """
-<p>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:State as the subject (see <a
-href="#state">state:state</a> 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.</p>
-""" .
-
-state:state
- a rdf:Property ;
- rdfs:range state:State ;
- lv2:documentation """
-<p>Predicate to relate a plugin instance to its State. 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:state [
- 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 this extension.</p>
-""" .
-
-state:mapPath
- a lv2:Feature ;
- rdfs:label "Support for storing paths in files" ;
- lv2:documentation """
-
-<p>This feature maps absolute paths to/from <q>abstract paths</q> which are
-stored in state. To support this feature a host must pass an LV2_Feature with
-URI LV2_STATE_MAP_PATH_URI and data pointed to an LV2_State_Map_Path to the
-plugin's LV2_State_Interface methods.</p>
-
-<p>The plugin MUST map <em>all</em> paths stored in its state (including in any
-files in its state). This is necessary to enable host to handle file system
-references correctly, e.g. for distribution or archival.</p>
-
-<p>For example, a plugin may write a path to a state file like so:</p>
-
-<pre class="c-code">
-void write_path(LV2_State_Map_Path* map_path, FILE* myfile, const char* path)
-{
- char* abstract_path = map_path->abstract_path(map_path->handle, path);
- fprintf(myfile, "%s", abstract_path);
- free(abstract_path);
-}
-</pre>
-
-<p>Then, later reload the path like so:</p>
-
-<pre class="c-code">
-char* read_path(LV2_State_Map_Path* map_path, FILE* myfile)
-{
- /* Obviously this is not production quality code! */
- char abstract_path[1024];
- fscanf(myfile, "%s", abstract_path);
- return map_path->absolute_path(map_path->handle, abstract_path);
-}
-</pre>
-""" .
-
-state:makePath
- a lv2:Feature ;
- rdfs:label "Support for creating new files and directories" ;
- lv2:documentation """
-
-<p>This feature allows plugins to create new files and/or directories. To
-support this feature the host passes an LV2_Feature with URI
-LV2_STATE_MAKE_PATH_URI and data pointed to an LV2_State_Make_Path to the
-plugin. The host may make this feature available only during save by passing
-it to LV2_State_Interface::save(), or available any time by passing it to
-LV2_Descriptor::instantiate(). If passed to LV2_State_Interface::save(), the
-feature MUST NOT be used beyond the scope of that call.</p>
-
-<p>The plugin is guaranteed a hierarchial namespace unique to that plugin
-instance, and may expect the returned path to have the requested path as a
-suffix. There is <em>one</em> such namespace, even if the feature is passed to
-both LV2_Descriptor::instantiate() <em>and</em>
-LV2_State_Interface::save(). Beyond this, the plugin MUST NOT make any
-assumptions about the returned paths.</p>
-
-<p>Like any other paths, the plugin MUST map these paths using <a
-href="#mapPath">state:mapPath</a> before storing them in state. The plugin
-MUST NOT assume these paths will be available across a save/restore otherwise,
-i.e. only mapped paths saved to state are persistent, any other created paths
-are temporary.</p>
-
-<p>For example, a plugin may create a file in a subdirectory like so:</p>
-
-<pre class="c-code">
-char* save_myfile(LV2_State_Make_Path* make_path)
-{
- char* path = make_path->path(make_path->handle, "foo/bar/myfile.txt");
- FILE* myfile = fopen(path, 'w');
- fprintf(myfile, "Hello");
- fclose(myfile);
- return path;
-}
-</pre>
-""" .
-
-state:Path
- a rdfs:Class ;
- rdfs:label "Path" ;
- lv2:documentation """
-<p>A path to a file or directory.</p>
-
-<p>The format of a state:Path is a C string, possibly escaped or otherwise
-restricted in a system-specific manner. This URI (LV2_STATE_PATH_URI), mapped
-to an integer, MUST be used as the <code>type</code> parameter for any files
-passed to the LV2_State_Store_Function; and will likewise be returned by the
-corresponding call to the LV2_State_Retrieve_Function.</p>
-
-<p>When storing and retrieving a path, the plugin MUST NOT assume the same path
-will be restored. However, the restored path will refer to a file with
-equivalent contents to the original.</p>
-""" .