diff options
Diffstat (limited to 'lv2/state')
| -rw-r--r-- | lv2/state/lv2-state.doap.ttl | 67 | ||||
| -rw-r--r-- | lv2/state/manifest.ttl | 8 | ||||
| -rw-r--r-- | lv2/state/state.h | 362 | ||||
| -rw-r--r-- | lv2/state/state.ttl | 382 |
4 files changed, 819 insertions, 0 deletions
diff --git a/lv2/state/lv2-state.doap.ttl b/lv2/state/lv2-state.doap.ttl new file mode 100644 index 0000000..4ad6089 --- /dev/null +++ b/lv2/state/lv2-state.doap.ttl @@ -0,0 +1,67 @@ +@prefix dcs: <http://ontologi.es/doap-changeset#> . +@prefix doap: <http://usefulinc.com/ns/doap#> . +@prefix foaf: <http://xmlns.com/foaf/0.1/> . +@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . + +<http://lv2plug.in/ns/ext/state> + a doap:Project ; + doap:created "2010-11-09" ; + doap:name "LV2 State" ; + doap:shortdesc "An interface for LV2 plugins to save and restore state." ; + doap:license <http://opensource.org/licenses/isc> ; + doap:developer <http://lv2plug.in/ns/meta#paniq> , + <http://drobilla.net/drobilla#me> ; + doap:maintainer <http://drobilla.net/drobilla#me> ; + doap:release [ + doap:revision "2.4" ; + doap:created "2019-02-03" ; + doap:file-release <http://lv2plug.in/spec/lv2-1.16.0.tar.bz2> ; + dcs:blame <http://drobilla.net/drobilla#me> ; + dcs:changeset [ + dcs:item [ + rdfs:label "Add state:StateChanged for notification events." + ] + ] + ] , [ + doap:revision "2.2" ; + doap:created "2016-07-31" ; + doap:file-release <http://lv2plug.in/spec/lv2-1.14.0.tar.bz2> ; + dcs:blame <http://drobilla.net/drobilla#me> ; + dcs:changeset [ + dcs:item [ + rdfs:label "Add LV2_STATE_ERR_NO_SPACE status flag." + ] , [ + rdfs:label "Add state:threadSafeRestore feature for dropout-free state restoration." + ] + ] + ] , [ + doap:revision "2.0" ; + doap:created "2013-01-16" ; + doap:file-release <http://lv2plug.in/spec/lv2-1.4.0.tar.bz2> ; + dcs:blame <http://drobilla.net/drobilla#me> ; + dcs:changeset [ + dcs:item [ + rdfs:label "Add state:loadDefaultState feature so plugins can have their default state loaded without hard-coding default state as a special case." + ] + ] + ] , [ + doap:revision "1.2" ; + doap:created "2012-10-14" ; + doap:file-release <http://lv2plug.in/spec/lv2-1.2.0.tar.bz2> ; + dcs:blame <http://drobilla.net/drobilla#me> ; + dcs:changeset [ + dcs:item [ + rdfs:label "Use consistent label style." + ] + ] + ] , [ + doap:revision "1.0" ; + doap:created "2012-04-17" ; + doap:file-release <http://lv2plug.in/spec/lv2-1.0.0.tar.bz2> ; + dcs:blame <http://drobilla.net/drobilla#me> ; + dcs:changeset [ + dcs:item [ + rdfs:label "Initial release." + ] + ] + ] . diff --git a/lv2/state/manifest.ttl b/lv2/state/manifest.ttl new file mode 100644 index 0000000..e2d4d30 --- /dev/null +++ b/lv2/state/manifest.ttl @@ -0,0 +1,8 @@ +@prefix lv2: <http://lv2plug.in/ns/lv2core#> . +@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . + +<http://lv2plug.in/ns/ext/state> + a lv2:Specification ; + lv2:minorVersion 2 ; + lv2:microVersion 4 ; + rdfs:seeAlso <state.ttl> . diff --git a/lv2/state/state.h b/lv2/state/state.h new file mode 100644 index 0000000..1005d50 --- /dev/null +++ b/lv2/state/state.h @@ -0,0 +1,362 @@ +/* + Copyright 2010-2016 David Robillard <http://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. +*/ + +/** + @defgroup state State + + An interface for LV2 plugins to save and restore state, see + <http://lv2plug.in/ns/ext/state> for details. + + @{ +*/ + +#ifndef LV2_STATE_H +#define LV2_STATE_H + +#include "lv2/core/lv2.h" + +#include <stdbool.h> +#include <stddef.h> +#include <stdint.h> + +#define LV2_STATE_URI "http://lv2plug.in/ns/ext/state" ///< http://lv2plug.in/ns/ext/state +#define LV2_STATE_PREFIX LV2_STATE_URI "#" ///< http://lv2plug.in/ns/ext/state# + +#define LV2_STATE__State LV2_STATE_PREFIX "State" ///< http://lv2plug.in/ns/ext/state#State +#define LV2_STATE__interface LV2_STATE_PREFIX "interface" ///< http://lv2plug.in/ns/ext/state#interface +#define LV2_STATE__loadDefaultState LV2_STATE_PREFIX "loadDefaultState" ///< http://lv2plug.in/ns/ext/state#loadDefaultState +#define LV2_STATE__makePath LV2_STATE_PREFIX "makePath" ///< http://lv2plug.in/ns/ext/state#makePath +#define LV2_STATE__mapPath LV2_STATE_PREFIX "mapPath" ///< http://lv2plug.in/ns/ext/state#mapPath +#define LV2_STATE__state LV2_STATE_PREFIX "state" ///< http://lv2plug.in/ns/ext/state#state +#define LV2_STATE__threadSafeRestore LV2_STATE_PREFIX "threadSafeRestore" ///< http://lv2plug.in/ns/ext/state#threadSafeRestore +#define LV2_STATE__StateChanged LV2_STATE_PREFIX "StateChanged" ///< http://lv2plug.in/ns/ext/state#StateChanged + +#ifdef __cplusplus +extern "C" { +#endif + +typedef void* LV2_State_Handle; ///< Opaque handle for state save/restore +typedef void* LV2_State_Map_Path_Handle; ///< Opaque handle for state:mapPath feature +typedef void* LV2_State_Make_Path_Handle; ///< Opaque handle for state:makePath feature + +/** + Flags describing value characteristics. + + These flags are used along with the value's type URI to determine how to + (de-)serialise the value data, or whether it is even possible to do so. +*/ +typedef enum { + /** + Plain Old Data. + + Values with this flag contain no pointers or references to other areas + of memory. It is safe to copy POD values with a simple memcpy and store + them for the duration of the process. A POD value is not necessarily + safe to trasmit between processes or machines (e.g. filenames are POD), + see LV2_STATE_IS_PORTABLE for details. + + Implementations MUST NOT attempt to copy or serialise a non-POD value if + they do not understand its type (and thus know how to correctly do so). + */ + LV2_STATE_IS_POD = 1, + + /** + Portable (architecture independent) data. + + Values with this flag are in a format that is usable on any + architecture. A portable value saved on one machine can be restored on + another machine regardless of architecture. The format of portable + values MUST NOT depend on architecture-specific properties like + endianness or alignment. Portable values MUST NOT contain filenames. + */ + LV2_STATE_IS_PORTABLE = 1 << 1, + + /** + Native data. + + This flag is used by the host to indicate that the saved data is only + going to be used locally in the currently running process (e.g. for + instance duplication or snapshots), so the plugin should use the most + efficient representation possible and not worry about serialisation + and portability. + */ + LV2_STATE_IS_NATIVE = 1 << 2 +} LV2_State_Flags; + +/** A status code for state functions. */ +typedef enum { + LV2_STATE_SUCCESS = 0, /**< Completed successfully. */ + LV2_STATE_ERR_UNKNOWN = 1, /**< Unknown error. */ + LV2_STATE_ERR_BAD_TYPE = 2, /**< Failed due to unsupported type. */ + LV2_STATE_ERR_BAD_FLAGS = 3, /**< Failed due to unsupported flags. */ + LV2_STATE_ERR_NO_FEATURE = 4, /**< Failed due to missing features. */ + LV2_STATE_ERR_NO_PROPERTY = 5, /**< Failed due to missing property. */ + LV2_STATE_ERR_NO_SPACE = 6 /**< Failed due to insufficient space. */ +} LV2_State_Status; + +/** + A host-provided function to store a property. + @param handle Must be the handle passed to LV2_State_Interface.save(). + @param key The key to store `value` under (URID). + @param value Pointer to the value to be stored. + @param size The size of `value` in bytes. + @param type The type of `value` (URID). + @param flags LV2_State_Flags for `value`. + @return 0 on success, otherwise a non-zero error code. + + The host passes a callback of this type to LV2_State_Interface.save(). This + callback is called repeatedly by the plugin to store all the properties that + describe its current state. + + DO NOT INVENT NONSENSE URI SCHEMES FOR THE KEY. Best is to use keys from + existing vocabularies. If nothing appropriate is available, use http URIs + that point to somewhere you can host documents so documentation can be made + resolvable (e.g. a child of the plugin or project URI). If this is not + possible, invent a URN scheme, e.g. urn:myproj:whatever. The plugin MUST + NOT pass an invalid URI key. + + The host MAY fail to store a property for whatever reason, but SHOULD + store any property that is LV2_STATE_IS_POD and LV2_STATE_IS_PORTABLE. + Implementations SHOULD use the types from the LV2 Atom extension + (http://lv2plug.in/ns/ext/atom) wherever possible. The plugin SHOULD + attempt to fall-back and avoid the error if possible. + + Note that `size` MUST be > 0, and `value` MUST point to a valid region of + memory `size` bytes long (this is required to make restore unambiguous). + + The plugin MUST NOT attempt to use this function outside of the + LV2_State_Interface.restore() context. +*/ +typedef LV2_State_Status (*LV2_State_Store_Function)( + LV2_State_Handle handle, + uint32_t key, + const void* value, + size_t size, + uint32_t type, + uint32_t flags); + +/** + A host-provided function to retrieve a property. + @param handle Must be the handle passed to LV2_State_Interface.restore(). + @param key The key of the property to retrieve (URID). + @param size (Output) If non-NULL, set to the size of the restored value. + @param type (Output) If non-NULL, set to the type of the restored value. + @param flags (Output) If non-NULL, set to the flags for the restored value. + @return A pointer to the restored value (object), or NULL if no value + has been stored under `key`. + + A callback of this type is passed by the host to + LV2_State_Interface.restore(). This callback is called repeatedly by the + plugin to retrieve any properties it requires to restore its state. + + The returned value MUST remain valid until LV2_State_Interface.restore() + returns. The plugin MUST NOT attempt to use this function, or any value + returned from it, outside of the LV2_State_Interface.restore() context. +*/ +typedef const void* (*LV2_State_Retrieve_Function)( + LV2_State_Handle handle, + uint32_t key, + size_t* size, + uint32_t* type, + uint32_t* flags); + +/** + LV2 Plugin State Interface. + + When the plugin's extension_data is called with argument + LV2_STATE__interface, the plugin MUST return an LV2_State_Interface + structure, which remains valid for the lifetime of the plugin. + + The host can use the contained function pointers to save and restore the + state of a plugin instance at any time, provided the threading restrictions + of the functions are met. + + Stored data is only guaranteed to be compatible between instances of plugins + with the same URI (i.e. if a change to a plugin would cause a fatal error + when restoring state saved by a previous version of that plugin, the plugin + URI MUST change just as it must when ports change incompatibly). Plugin + authors should consider this possibility, and always store sensible data + with meaningful types to avoid such problems in the future. +*/ +typedef struct _LV2_State_Interface { + /** + Save plugin state using a host-provided `store` callback. + + @param instance The instance handle of the plugin. + @param store The host-provided store callback. + @param handle An opaque pointer to host data which MUST be passed as the + handle parameter to `store` if it is called. + @param flags Flags describing desired properties of this save. These + flags may be used to determine the most appropriate values to store. + @param features Extensible parameter for passing any additional + features to be used for this save. + + The plugin is expected to store everything necessary to completely + restore its state later. Plugins SHOULD store simple POD data whenever + possible, and consider the possibility of state being restored much + later on a different machine. + + The `handle` pointer and `store` function MUST NOT be used + beyond the scope of save(). + + This function has its own special threading class: it may not be called + concurrently with any "Instantiation" function, but it may be called + concurrently with functions in any other class, unless the definition of + that class prohibits it (e.g. it may not be called concurrently with a + "Discovery" function, but it may be called concurrently with an "Audio" + function. The plugin is responsible for any locking or lock-free + techniques necessary to make this possible. + + Note that in the simple case where state is only modified by restore(), + there are no synchronization issues since save() is never called + concurrently with restore() (though run() may read it during a save). + + Plugins that dynamically modify state while running, however, must take + care to do so in such a way that a concurrent call to save() will save a + consistent representation of plugin state for a single instant in time. + */ + LV2_State_Status (*save)(LV2_Handle instance, + LV2_State_Store_Function store, + LV2_State_Handle handle, + uint32_t flags, + const LV2_Feature *const * features); + + /** + Restore plugin state using a host-provided `retrieve` callback. + + @param instance The instance handle of the plugin. + @param retrieve The host-provided retrieve callback. + @param handle An opaque pointer to host data which MUST be passed as the + handle parameter to `retrieve` if it is called. + @param flags Currently unused. + @param features Extensible parameter for passing any additional + features to be used for this restore. + + The plugin MAY assume a restored value was set by a previous call to + LV2_State_Interface.save() by a plugin with the same URI. + + The plugin MUST gracefully fall back to a default value when a value can + not be retrieved. This allows the host to reset the plugin state with + an empty map. + + The `handle` pointer and `store` function MUST NOT be used + beyond the scope of restore(). + + This function is in the "Instantiation" threading class as defined by + LV2. This means it MUST NOT be called concurrently with any other + function on the same plugin instance. + */ + LV2_State_Status (*restore)(LV2_Handle instance, + LV2_State_Retrieve_Function retrieve, + LV2_State_Handle handle, + uint32_t flags, + const LV2_Feature *const * features); +} LV2_State_Interface; + +/** + Feature data for state:mapPath (@ref LV2_STATE__mapPath). +*/ +typedef struct { + /** + Opaque host data. + */ + LV2_State_Map_Path_Handle handle; + + /** + Map an absolute path to an abstract path for use in plugin state. + @param handle MUST be the `handle` member of this struct. + @param absolute_path The absolute path of a file. + @return An abstract path suitable for use in plugin state. + + The plugin MUST use this function to map any paths that will be stored + in plugin state. The returned value is an abstract path which MAY not + be an actual file system path; absolute_path() MUST be used to map + it to an actual path in order to use the file. + + Plugins MUST NOT make any assumptions about abstract paths except that + they can be mapped back to the absolute path of the "same" file (though + not necessarily the same original path) using absolute_path(). + + This function may only be called within the context of + LV2_State_Interface methods. The caller is responsible for freeing the + returned value with free(). + */ + char* (*abstract_path)(LV2_State_Map_Path_Handle handle, + const char* absolute_path); + + /** + Map an abstract path from plugin state to an absolute path. + @param handle MUST be the `handle` member of this struct. + @param abstract_path An abstract path (e.g. a path from plugin state). + @return An absolute file system path. + + The plugin MUST use this function in order to actually open or otherwise + use any paths loaded from plugin state. + + This function may only be called within the context of + LV2_State_Interface methods. The caller is responsible for freeing the + returned value with free(). + */ + char* (*absolute_path)(LV2_State_Map_Path_Handle handle, + const char* abstract_path); +} LV2_State_Map_Path; + +/** + Feature data for state:makePath (@ref LV2_STATE__makePath). +*/ +typedef struct { + /** + Opaque host data. + */ + LV2_State_Make_Path_Handle handle; + + /** + Return a path the plugin may use to create a new file. + @param handle MUST be the `handle` member of this struct. + @param path The path of the new file within a namespace unique to this + plugin instance. + @return The absolute path to use for the new file. + + This function can be used by plugins to create files and directories, + either at state saving time (if this feature is passed to + LV2_State_Interface.save()) or any time (if this feature is passed to + LV2_Descriptor.instantiate()). + + The host MUST do whatever is necessary for the plugin to be able to + create a file at the returned path (e.g. using fopen), including + creating any leading directories. + + If this function is passed to LV2_Descriptor.instantiate(), it may be + called from any non-realtime context. If it is passed to + LV2_State_Interface.save(), it may only be called within the dynamic + scope of that function call. + + The caller is responsible for freeing the returned value with free(). + */ + char* (*path)(LV2_State_Make_Path_Handle handle, + const char* path); +} LV2_State_Make_Path; + +#ifdef __cplusplus +} /* extern "C" */ +#endif + +#endif /* LV2_STATE_H */ + +/** + @} +*/ diff --git a/lv2/state/state.ttl b/lv2/state/state.ttl new file mode 100644 index 0000000..c86fea7 --- /dev/null +++ b/lv2/state/state.ttl @@ -0,0 +1,382 @@ +@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://lv2plug.in/ns/ext/state> + a lv2:Specification ; + rdfs:seeAlso <state.h> , + <lv2-state.doap.ttl> ; + lv2:documentation """ +<p>This extension defines a simple mechanism which allows hosts to save and +restore a plugin instance's state. The goal is for an 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> defined here is conceptually a key:value dictionary, with +URI keys and values of any type. For performance reasons the key and value +type are actually a <q>URID</q>, a URI mapped to an integer. A single +key:value pair is called a <q>property</q>.</p> + +<p>This state model is simple yet has many benefits:</p> +<ul> + <li>Both fast and extensible thanks to URID keys.</li> + <li>No limitations on possible value types.</li> + <li>Easy to serialise in almost any format.</li> + <li>Easy to store in a typical <q>map</q> or <q>dictionary</q> data + structure.</li> + <li>Elegantly described in Turtle, so state can be described in LV2 data + files (including presets).</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>Keys <em>may</em> be well-defined and used meaningfully across several + implementations.</li> + <li>State <em>may</em> be dynamic, but plugins are not required to have a + dynamic dictionary data structure available.</li> +</ul> + +<p>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>Since value types are defined by URI, any type is possible. However, a set +of standard types is defined by the <a href="../atom/atom.html">LV2 Atom</a> +extension. Use of these types is recommended. Hosts MUST implement at least +<a href="../atom/atom.html#String">atom:String</a>, which is simply a C +string.</p> + +<h3>Referring to Files</h3> + +<p>Plugins may need to refer to existing 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 state:mapPath for details. Plugins MUST use the type <a +href="../atom/atom.html#Path">atom:Path</a> for all paths in their state.</p> + +<p>Plugins are strongly encouraged to avoid creating files, instead storing all +state as properties. However, occasionally the ability to create files is +necessary. To make this possible, the host can provide the feature +state:makePath which allocates paths for plugin-created files. Plugins MUST +NOT create files in any other locations.</p> + +<h3>Plugin Code Example</h3> + +<pre class="c-code"> + +/* Namespace for this plugin's keys. This SHOULD be something that could be + published as a document, even if that document does not exist right now. +*/ +#define NS_MY "http://example.org/myplugin/schema#" + +#define DEFAULT_GREETING "Hello" + +LV2_Handle +my_instantiate(...) +{ + MyPlugin* plugin = ...; + plugin->uris.atom_String = map_uri(LV2_ATOM__String); + plugin->uris.my_greeting = map_uri(NS_MY "greeting"); + plugin->state.greeting = strdup(DEFAULT_GREETING); + return plugin; +} + +LV2_State_Status +my_save(LV2_Handle instance, + LV2_State_Store_Function store, + LV2_State_Handle handle, + uint32_t flags, + const LV2_Feature *const * features) +{ + MyPlugin* plugin = (MyPlugin*)instance; + const char* greeting = plugin->state.greeting; + + store(handle, + plugin->uris.my_greeting, + greeting, + strlen(greeting) + 1, // Careful! Need space for terminator + plugin->uris.atom_String, + LV2_STATE_IS_POD | LV2_STATE_IS_PORTABLE); + + return LV2_STATE_SUCCESS; +} + +LV2_State_Status +my_restore(LV2_Handle instance, + LV2_State_Retrieve_Function retrieve, + LV2_State_Handle 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.my_greeting, &size, &type, &flags); + + if (greeting) { + free(plugin->state->greeting); + plugin->state->greeting = strdup(greeting); + } else { + plugin->state->greeting = strdup(DEFAULT_GREETING); + } + + return LV2_STATE_SUCCESS; +} + +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)) { + return &state_iface; + } +} +</pre> + +<h3>Host Code Example</h3> + +<pre class="c-code"> +LV2_State_Status +store_callback(LV2_State_Handle handle, + uint32_t key, + const void* value, + size_t size, + uint32_t type, + uint32_t flags) +{ + if ((flags & LV2_STATE_IS_POD)) { + /* We only care about POD since we're keeping state in memory only. + For disk or network use, LV2_STATE_IS_PORTABLE must also be checked. + */ + Map* state_map = (Map*)handle; + state_map->insert(key, Value(copy(value), size, type)); + return 0; + } else { + return 1; /* Non-POD events are unsupported. */ + } +} + +Map +get_plugin_state(LV2_Handle instance) +{ + LV2_State* state = instance.extension_data(LV2_STATE__interface); + Map state_map; + /** Request a fast/native/POD save, since we're just copying in memory */ + state.save(instance, store_callback, &state_map, + LV2_STATE_IS_POD|LV2_STATE_IS_NATIVE); + return state_map; +} +</pre> + +<h3>Extensions to this Specification</h3> + +<p>It is likely that other interfaces for working with plugin state will be +developed as needed. This is encouraged, however everything SHOULD work within +the state <em>model</em> defined here. That is, <strong>do not complicate the +state model</strong>. Implementations can assume the following:</p> + +<ul> +<li>The current port values and state dictionary completely describe a plugin +instance, at least well enough that saving and restoring will yield an +<q>identical</q> instance from the user's perspective.</li> +<li>Hosts are not expected to save and/or restore any other attributes of a +plugin instance.</li> +</ul> + +<h3>The <q>Property Principle</q></h3> + +<p>The main benefit of this meaningful state model is that it can double as a +plugin control/query mechanism. For plugins that require more advanced control +than simple control ports, instead of defining a set of commands, define +properties whose values can be set appropriately. This provides both a way to +control and save that state <q>for free</q>, since there is no need to define +commands <em>and</em> a set of properties for storing their effects. In +particular, this is a good way for UIs to achieve more advanced control of +plugins.</p> + +<p>This <q>property principle</q> is summed up in the phrase: +<q>Don't stop; set playing to false</q>.</p> + +<p>This extension does not define a dynamic mechanism for state access and +manipulation. The <a href="../patch/patch.html">LV2 Patch</a> extension +defines a generic set of messages which can be used to access or manipulate +properties, and the <a href="../atom/atom.html">LV2 Atom</a> extension defines +a port type and data container capable of transmitting those messages.</p> +""" . + +state:interface + a 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 URI +LV2_STATE__interface.</p> + +<p>The plugin data file should describe this like so:</p> +<pre class="turtle-code"> +@prefix state: <http://lv2plug.in/ns/ext/state#> . + +<plugin> + a lv2:Plugin ; + lv2:extensionData state:interface . +</pre> +""" . + +state:State + a rdfs:Class ; + rdfs:label "State" ; + lv2:documentation """ +<p>A state dictionary. This type should be used wherever instance state is +described. The properties of a resource with this type correspond directly to +the properties of the state dictionary (except the property that states it has +this type).</p> +""" . + +state:loadDefaultState + a lv2:Feature ; + lv2:documentation """ +<p>This feature indicates that the plugin has default state listed with the +state:state property which should be loaded by the host before running the +plugin. Requiring this feature allows plugins to implement a single state +loading mechanism which works for initialisation as well as restoration, +without having to hard-code default state.</p> + +<p>To support this feature, the host MUST <q>restore</q> the default state +after instantiating the plugin but before calling run().</p> +""" . + +state:state + a rdf:Property ; + rdfs:label "state" ; + rdfs:range state:State ; + lv2:documentation """ +<p>The state of this instance. This property may be used anywhere a state +needs to be described, for example:</p> + +<pre class="turtle-code"> +@prefix eg: <http://example.org/> . + +<plugin-instance> + state:state [ + eg:somekey "some value" ; + eg:someotherkey "some other value" ; + eg:favourite-number 2 + ] . +</pre> +""" . + +state:mapPath + a lv2:Feature ; + rdfs:label "map file paths" ; + 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__mapPath 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 those +inside 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 "create new file paths" ; + 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__makePath 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 hierarchical 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 state:mapPath +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, "I am some data"); + fclose(myfile); + return path; +} +</pre> +""" . + +state:threadSafeRestore + a lv2:Feature ; + rdfs:label "thread-safe restore" ; + lv2:documentation """ +<p>If a plugin supports this feature, its LV2_State_Interface::restore method +is thread-safe and may be called concurrently with audio class functions.</p> + +<p>To support this feature, the host MUST pass a <a +href="../worker/worker.html#schedule">work:schedule</a> feature to the restore +method, which will be used to complete the state restoration. The usual +mechanics of the worker apply: the host will call the plugin's work method, +which emits a response which is later applied in the audio thread.</p> + +<p>The host is not required to block run() while restore() and work() load the +state, so this feature allows state to be restored without dropouts.</p> +""" . + +state:Changed + a rdfs:Class ; + rdfs:label "State changed" ; + lv2:documentation """ +<p>A notification that the internal state of the plugin has been changed in a +way that the host can not otherwise know about.</p> + +<p>This is a one-way notification, intended to be used as the type of an <a +href="../atom/atom.html#Object">Object</a> sent from plugins when +necessary.</p> + +<p>Plugins SHOULD emit such an event whenever a change has occurred that would +result in a different state being saved, but not when the host explicity makes +a change which it knows is likely to have that effect, such as changing a +parameter.</p> +""" . |