Descriptor for a Type of Plugin. More...
#include <lv2.h>
Data Fields | |
const char * | URI |
A globally unique, case-sensitive identifier for this plugin type. | |
LV2_Handle(* | instantiate )(const struct _LV2_Descriptor *descriptor, double sample_rate, const char *bundle_path, const LV2_Feature *const *features) |
Function pointer that instantiates a plugin. | |
void(* | connect_port )(LV2_Handle instance, uint32_t port, void *data_location) |
Function pointer that connects a port on a plugin instance to a memory location where the block of data for the port will be read/written. | |
void(* | activate )(LV2_Handle instance) |
Function pointer that initialises a plugin instance and activates it for use. | |
void(* | run )(LV2_Handle instance, uint32_t sample_count) |
Function pointer that runs a plugin instance for a block. | |
void(* | deactivate )(LV2_Handle instance) |
This is the counterpart to activate() (see above). | |
void(* | cleanup )(LV2_Handle instance) |
This is the counterpart to instantiate() (see above). | |
const void *(* | extension_data )(const char *uri) |
Function pointer that can be used to return additional instance data for a plugin defined by some extenion (e.g. |
Descriptor for a Type of Plugin.
This structure is used to describe a plugin type. It provides a number of functions to instantiate it, link it to buffers and run it.
const char* _LV2_Descriptor::URI |
A globally unique, case-sensitive identifier for this plugin type.
All plugins with the same URI MUST be compatible in terms of 'port signature', meaning they have the same number of ports, same port shortnames, and roughly the same functionality. URIs should probably contain a version number (or similar) for this reason.
Rationale: When serializing session/patch/etc files, hosts MUST refer to a loaded plugin by the plugin URI only. In the future loading a plugin with this URI MUST yield a plugin with the same ports (etc) which is 100% compatible.
LV2_Handle(* _LV2_Descriptor::instantiate)(const struct _LV2_Descriptor *descriptor, double sample_rate, const char *bundle_path, const LV2_Feature *const *features) |
Function pointer that instantiates a plugin.
A handle is returned indicating the new plugin instance. The instantiation function accepts a sample rate as a parameter as well as the plugin descriptor from which this instantiate function was found. This function must return NULL if instantiation fails.
bundle_path is a string of the path to the LV2 bundle which contains this plugin binary. It MUST include the trailing directory separator (e.g. '/') so that BundlePath + filename gives the path to a file in the bundle.
features is a NULL terminated array of LV2_Feature structs which represent the features the host supports. Plugins may refuse to instantiate if required features are not found here (however hosts SHOULD NOT use this as a discovery mechanism, instead reading the data file before attempting to instantiate the plugin). This array must always exist; if a host has no features, it MUST pass a single element array containing NULL (to simplify plugins).
Note that instance initialisation should generally occur in activate() rather than here. If a host calls instantiate, it MUST call cleanup() at some point in the future.
void(* _LV2_Descriptor::connect_port)(LV2_Handle instance, uint32_t port, void *data_location) |
Function pointer that connects a port on a plugin instance to a memory location where the block of data for the port will be read/written.
The data location is expected to be of the type defined in the plugin's data file (e.g. an array of float for an lv2:AudioPort). Memory issues are managed by the host. The plugin must read/write the data at these locations every time run() is called, data present at the time of this connection call MUST NOT be considered meaningful.
The host MUST NOT try to connect a data buffer to a port index that is not defined in the RDF data for the plugin. If it does, the plugin's behaviour is undefined.
connect_port() may be called more than once for a plugin instance to allow the host to change the buffers that the plugin is reading or writing. These calls may be made before or after activate() or deactivate() calls. Note that there may be realtime constraints on connect_port (see lv2:hardRTCapable in lv2.ttl).
connect_port() MUST be called at least once for each port before run() is called. The plugin must pay careful attention to the block size passed to the run function as the block allocated may only just be large enough to contain the block of data (typically samples), and is not guaranteed to be constant.
Plugin writers should be aware that the host may elect to use the same buffer for more than one port and even use the same buffer for both input and output (see lv2:inPlaceBroken in lv2.ttl). However, overlapped buffers or use of a single buffer for both audio and control data may result in unexpected behaviour.
If the plugin has the feature lv2:hardRTCapable then there are various things that the plugin MUST NOT do within the connect_port() function (see lv2.ttl).
void(* _LV2_Descriptor::activate)(LV2_Handle instance) |
Function pointer that initialises a plugin instance and activates it for use.
This is separated from instantiate() to aid real-time support and so that hosts can reinitialise a plugin instance by calling deactivate() and then activate(). In this case the plugin instance must reset all state information dependent on the history of the plugin instance except for any data locations provided by connect_port(). If there is nothing for activate() to do then the plugin writer may provide a NULL rather than an empty function.
When present, hosts MUST call this function once before run() is called for the first time. This call SHOULD be made as close to the run() call as possible and indicates to real-time plugins that they are now live, however plugins MUST NOT rely on a prompt call to run() after activate(). activate() may not be called again unless deactivate() is called first (after which activate() may be called again, followed by deactivate, etc. etc.). If a host calls activate, it MUST call deactivate at some point in the future.
Note that connect_port() may be called before or after a call to activate().
void(* _LV2_Descriptor::run)(LV2_Handle instance, uint32_t sample_count) |
Function pointer that runs a plugin instance for a block.
Two parameters are required: the first is a handle to the particular instance to be run and the second indicates the block size (in samples) for which the plugin instance may run.
Note that if an activate() function exists then it must be called before run(). If deactivate() is called for a plugin instance then the plugin instance may not be reused until activate() has been called again.
If the plugin has the feature lv2:hardRTCapable then there are various things that the plugin MUST NOT do within the run() function (see lv2.ttl).
void(* _LV2_Descriptor::deactivate)(LV2_Handle instance) |
This is the counterpart to activate() (see above).
If there is nothing for deactivate() to do then the plugin writer may provide a NULL rather than an empty function.
Hosts must deactivate all activated units after they have been run() for the last time. This call SHOULD be made as close to the last run() call as possible and indicates to real-time plugins that they are no longer live, however plugins MUST NOT rely on prompt deactivation. Note that connect_port() may be called before or after a call to deactivate().
Note that deactivation is not similar to pausing as the plugin instance will be reinitialised when activate() is called to reuse it. Hosts MUST NOT call deactivate() unless activate() was previously called.
void(* _LV2_Descriptor::cleanup)(LV2_Handle instance) |
This is the counterpart to instantiate() (see above).
Once an instance of a plugin has been finished with it can be deleted using this function. The instance handle passed ceases to be valid after this call.
If activate() was called for a plugin instance then a corresponding call to deactivate() MUST be made before cleanup() is called. Hosts MUST NOT call cleanup() unless instantiate() was previously called.
const void*(* _LV2_Descriptor::extension_data)(const char *uri) |
Function pointer that can be used to return additional instance data for a plugin defined by some extenion (e.g.
a struct containing additional function pointers).
The actual type and meaning of the returned object MUST be specified precisely by the extension if it defines any extra data. If a particular extension does not define extra instance data, this function MUST return NULL for that extension's URI. If a plugin does not support any extensions that define extra instance data, this function pointer may be set to NULL rather than providing an empty function.
The only parameter is the URI of the extension. The plugin MUST return NULL if it does not support the extension, but hosts SHOULD NOT use this as a discovery method (e.g. hosts should only call this function for extensions known to be supported by the plugin from the data file).
The host is never responsible for freeing the returned value.
NOTE: This function should return a struct (likely containing function pointers) and NOT a direct function pointer. Standard C and C++ do not allow type casts from void* to a function pointer type. To provide additional functions a struct should be returned containing the extra function pointers (which is valid standard code, and a much better idea for extensibility anyway).