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Diffstat (limited to 'ext/persist.lv2/persist.h')
| -rw-r--r-- | ext/persist.lv2/persist.h | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/ext/persist.lv2/persist.h b/ext/persist.lv2/persist.h new file mode 100644 index 0000000..928a297 --- /dev/null +++ b/ext/persist.lv2/persist.h @@ -0,0 +1,177 @@ +/* lv2_persist.h - C header file for the LV2 Persist extension. + * Copyright (C) 2010 Leonard Ritter <paniq@paniq.org> + * + * This header is free software; you can redistribute it and/or modify it + * under the terms of the GNU Lesser General Public License as published + * by the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This header is distributed in the hope that it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public + * License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with this header; if not, write to the Free Software Foundation, + * Inc., 59 Temple Place, Suite 330, Boston, MA 01222-1307 USA + */ + +/** @file + * C header for the LV2 Persist extension <http://lv2plug.in/ns/ext/persist>. + */ + +#ifndef LV2_PERSIST_H +#define LV2_PERSIST_H + +#ifdef __cplusplus +extern "C" { +#endif + +#define LV2_PERSIST_URI "http://lv2plug.in/ns/ext/persist" + +/** Causes the host to store a value under a given key. + * + * This callback is passed by the host to LV2_Persist.save(). + * @param callback_data Must be the callback_data passed to LV2_Persist.save(). + * @param key The URI key (RDF predicate) under which the value is to be stored. + * @param value Pointer to the value (RDF object) to be stored. + * @param size The size of the data at @a value in bytes. + * @param type The type of @a value, as a URI mapped to an integer. + * + * Unless @a type is 0, @a value is guaranteed to be POD (i.e. a region + * of memory that does not contain pointers and can safely be copied + * and persisted indefinitely with a simple memcpy). If @a type is 0, + * then @a value is a reference, as defined by the LV2 Atom extension + * <http://lv2plug.in/ns/ext/atom/>. Hosts are not required to support + * references, a plugin MUST NOT expect a host to persist references unless + * the host supports the feature <http://lv2plug.in/ns/ext/atom#blobSupport>. + * + * Note that @a size MUST be > 0, and @a value MUST point to a valid region of + * memory @a size bytes long (this is required to make restore unambiguous). + * If only the key is of interest, store the empty string (which has size 1). + */ +typedef void (*LV2_Persist_Store_Function)( + void* callback_data, + const char* key, + const void* value, + size_t size, + uint32_t type); + +/** Causes the host to retrieve a value under a given key. + * + * This callback is passed by the host to LV2_Persist.restore(). + * @param callback_data Must be the callback_data passed to LV2_Persist.restore(). + * @param key The URI key (RDF predicate) under which a value has been stored. + * @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. + * @return A pointer to the restored value (RDF object), or NULL if no value + * has been stored under @a key. + * + * The returned value MUST remain valid until LV2_Persist.restore() returns. The plugin + * MUST NOT attempt to access a returned pointer outside of the LV2_Persist.restore() + * context (it MUST make a copy in order to do so). + */ +typedef const void* (*LV2_Persist_Retrieve_Function)( + void* callback_data, + const char* key, + size_t* size, + uint32_t* type); + +/** When the plugin's extension_data is called with argument LV2_PERSIST_URI, + * the plugin MUST return an LV2_Persist 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 + * for the given function are met). + * + * The typical use case is to save the plugin's state when a project is + * saved, and to restore the state when a project has been loaded. Other + * uses are possible (e.g. cloning plugin instances or taking a snapshot + * of plugin state). + * + * 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 a plugin's ports change). Plugin + * authors should consider this possibility, and always store sensible data + * with meaningful types to avoid such compatibility issues in the future. + */ +typedef struct _LV2_Persist { + /** Causes the plugin to save state data using a host-provided + * @a store callback. + * + * @param instance The instance handle of the plugin. + * @param store The host-provided store callback. + * @param callback_data An opaque pointer to host data, e.g. the map or + * file where the values are to be stored. If @a store is called, + * this MUST be passed as its callback_data parameter. + * + * The plugin is expected to store everything necessary to completely + * restore its state later (possibly much later, in a different + * process, on a completely different machine, etc.) + * + * The @a callback_data pointer and @a 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 point in time. The simplest way to do this is to modify a + * copy of the state map and atomically swap a pointer to the entire + * map once the changes are complete (for very large state maps, + * a purely functional map data structure would be more appropriate + * since a complete copy is not necessary). + */ + void (*save)(LV2_Handle instance, + LV2_Persist_Store_Function store, + void* callback_data); + + /** Causes the plugin to restore state data using a host-provided + * @a retrieve callback. + * + * @param instance The instance handle of the plugin. + * @param retrieve The host-provided retrieve callback. + * @param callback_data An opaque pointer to host data, e.g. the map or + * file from which the values are to be restored. If @a retrieve is + * called, this MUST be passed as its callback_data parameter. + * + * The plugin MAY assume a restored value was set by a previous call to + * LV2_Persist.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 @a callback_data pointer and @a 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. + */ + void (*restore)(LV2_Handle instance, + LV2_Persist_Retrieve_Function retrieve, + void* callback_data); + +} LV2_Persist; + +#ifdef __cplusplus +} /* extern "C" */ +#endif + +#endif /* LV2_PERSIST_H */ |