From 4db67120efca2d4c200d2e1ba5cf3d7b97cab97e Mon Sep 17 00:00:00 2001 From: David Robillard Date: Sat, 22 Sep 2018 20:38:01 +0200 Subject: Install standard headers to simpler include paths --- lv2/state/state.ttl | 382 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 382 insertions(+) create mode 100644 lv2/state/state.ttl (limited to 'lv2/state/state.ttl') 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: . +@prefix rdf: . +@prefix rdfs: . +@prefix state: . + + + a lv2:Specification ; + rdfs:seeAlso , + ; + lv2:documentation """ +

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 +completely described by port values (as with all LV2 plugins) and a +simple dictionary.

+ +

The state 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 URID, a URI mapped to an integer. A single +key:value pair is called a property.

+ +

This state model is simple yet has many benefits:

+
    +
  • Both fast and extensible thanks to URID keys.
    • +
  • No limitations on possible value types.
    • +
  • Easy to serialise in almost any format.
    • +
  • Easy to store in a typical map or dictionary data + structure.
    • +
  • Elegantly described in Turtle, so state can be described in LV2 data + files (including presets).
    • +
  • Does not impose any file formats, data structures, or file system + requirements.
    • +
  • Suitable for portable persistent state as well as fast in-memory + snapshots.
    • +
  • Keys may be well-defined and used meaningfully across several + implementations.
    • +
  • State may be dynamic, but plugins are not required to have a + dynamic dictionary data structure available.
    • +
+ +

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.

+ +

Since value types are defined by URI, any type is possible. However, a set +of standard types is defined by the LV2 Atom +extension. Use of these types is recommended. Hosts MUST implement at least +atom:String, which is simply a C +string.

+ +

Referring to Files

+ +

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 atom:Path for all paths in their state.

+ +

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.

+ +

Plugin Code Example

+ +
+
+/* 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;
+    }
+}
+
+ +

Host Code Example

+ +
+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;
+}
+
+ +

Extensions to this Specification

+ +

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 model defined here. That is, do not complicate the +state model. Implementations can assume the following:

+ +
    +
  • The current port values and state dictionary completely describe a plugin +instance, at least well enough that saving and restoring will yield an +identical instance from the user's perspective.
    • +
  • Hosts are not expected to save and/or restore any other attributes of a +plugin instance.
    • +
+ +

The Property Principle

+ +

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 for free, since there is no need to define +commands and a set of properties for storing their effects. In +particular, this is a good way for UIs to achieve more advanced control of +plugins.

+ +

This property principle is summed up in the phrase: +Don't stop; set playing to false.

+ +

This extension does not define a dynamic mechanism for state access and +manipulation. The LV2 Patch extension +defines a generic set of messages which can be used to access or manipulate +properties, and the LV2 Atom extension defines +a port type and data container capable of transmitting those messages.

+""" . + +state:interface + a lv2:ExtensionData ; + lv2:documentation """ +

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.

+ +

The plugin data file should describe this like so:

+
+@prefix state: <http://lv2plug.in/ns/ext/state#> .
+
+<plugin>
+    a lv2:Plugin ;
+    lv2:extensionData state:interface .
+
+""" . + +state:State + a rdfs:Class ; + rdfs:label "State" ; + lv2:documentation """ +

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).

+""" . + +state:loadDefaultState + a lv2:Feature ; + lv2:documentation """ +

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.

+ +

To support this feature, the host MUST restore the default state +after instantiating the plugin but before calling run().

+""" . + +state:state + a rdf:Property ; + rdfs:label "state" ; + rdfs:range state:State ; + lv2:documentation """ +

The state of this instance. This property may be used anywhere a state +needs to be described, for example:

+ +
+@prefix eg: <http://example.org/> .
+
+<plugin-instance>
+    state:state [
+        eg:somekey "some value" ;
+        eg:someotherkey "some other value" ;
+        eg:favourite-number 2
+    ] .
+
+""" . + +state:mapPath + a lv2:Feature ; + rdfs:label "map file paths" ; + lv2:documentation """ +

This feature maps absolute paths to/from abstract paths 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.

+ +

The plugin MUST map all 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.

+ +

For example, a plugin may write a path to a state file like so:

+ +
+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);
+}
+
+ +

Then, later reload the path like so:

+ +
+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);
+}
+
+""" . + +state:makePath + a lv2:Feature ; + rdfs:label "create new file paths" ; + lv2:documentation """ +

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.

+ +

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 one such namespace, even if the feature is passed to +both LV2_Descriptor::instantiate() and LV2_State_Interface::save(). +Beyond this, the plugin MUST NOT make any assumptions about the returned +paths.

+ +

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.

+ +

For example, a plugin may create a file in a subdirectory like so:

+ +
+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;
+}
+
+""" . + +state:threadSafeRestore + a lv2:Feature ; + rdfs:label "thread-safe restore" ; + lv2:documentation """ +

If a plugin supports this feature, its LV2_State_Interface::restore method +is thread-safe and may be called concurrently with audio class functions.

+ +

To support this feature, the host MUST pass a work:schedule 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.

+ +

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.

+""" . + +state:Changed + a rdfs:Class ; + rdfs:label "State changed" ; + lv2:documentation """ +

A notification that the internal state of the plugin has been changed in a +way that the host can not otherwise know about.

+ +

This is a one-way notification, intended to be used as the type of an Object sent from plugins when +necessary.

+ +

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.

+""" . -- cgit v1.2.1