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authorDavid Robillard <d@drobilla.net>2012-02-08 04:56:24 +0000
committerDavid Robillard <d@drobilla.net>2012-02-08 04:56:24 +0000
commited78bbe5ba12be1f9bcc736f14c51da6b4f639f3 (patch)
tree653a2dfe33f3923da45a38fc04ed2106f93528f3 /lv2/lv2plug.in/ns/ext/state/state.ttl
parentb617875c6f3ad439d25ae166da79df839ebfdc71 (diff)
downloadlv2-ed78bbe5ba12be1f9bcc736f14c51da6b4f639f3.tar.xz
Rearrange tree so top level can be used as an include path for standard style LV2 includes.
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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>
+""" .