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authorDavid Robillard <d@drobilla.net>2011-11-20 23:08:57 +0000
committerDavid Robillard <d@drobilla.net>2011-11-20 23:08:57 +0000
commit725d4a404b838da6b67d9da66228a1125bddef57 (patch)
treea1daab3d767c85b1b67ff3a9eb60d54721b2e5fc /ns/ext/state/state.ttl
parent5ae0165d6d0420e95e22c1451e319b9e83398c28 (diff)
downloadlv2-725d4a404b838da6b67d9da66228a1125bddef57.tar.xz
Lay out repository structure to match include and URI structure.
Treat lv2core like all the other specifications in gendoc.py.
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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>
+""" .