# LV2

An open and extensible audio plugin standard

Version | 1.18.10

Data Structures | Macros | Variables
URI Map
LV2

## Detailed Description

A feature for mapping URIs to integers.

This extension defines a simple mechanism for plugins to map URIs to integers, usually for performance reasons (e.g. processing events typed by URIs in real time). The expected use case is for plugins to map URIs to integers for things they 'understand' at instantiation time, and store those values for use in the audio thread without doing any string comparison. This allows the extensibility of RDF with the performance of integers (or centrally defined enumerations).

See http://lv2plug.in/ns/ext/uri-map for details.

## Data Structures
struct | LV2_URI_Map_Feature

## Macros
#define | LV2_URI_MAP_URI "http://lv2plug.in/ns/ext/uri-map"
#define | LV2_URI_MAP_PREFIX LV2_URI_MAP_URI "#"

## Variables
LV2_DEPRECATED typedef void * | LV2_URI_Map_Callback_Data

## Data Structure Documentation

## ◆ LV2_URI_Map_Feature

struct LV2_URI_Map_Feature

URI Map Feature.

To support this feature the host must pass an LV2_Feature struct to the plugin's instantiate method with URI "http://lv2plug.in/ns/ext/uri-map" and data pointed to an instance of this struct.

Data Fields
LV2_URI_Map_Callback_Data | callback_data | Opaque pointer to host data. The plugin MUST pass this to any call to functions in this struct. Otherwise, it must not be interpreted in any way.
  uint32_t(*)(LV2_URI_Map_Callback_Data callback_data, const char *map, const char *uri) | uri_to_id | Get the numeric ID of a URI from the host. Parameters
  callback_data | Must be the callback_data member of this struct.
  map | The 'context' of this URI. Certain extensions may define a URI that must be passed here with certain restrictions on the return value (e.g. limited range). This value may be NULL if the plugin needs an ID for a URI in general. Extensions SHOULD NOT define a context unless there is a specific need to do so, e.g. to restrict the range of the returned value.
  uri | The URI to be mapped to an integer ID.
This function is referentially transparent; any number of calls with the same arguments is guaranteed to return the same value over the life of a plugin instance (though the same URI may return different values with a different map parameter). However, this function is not necessarily very fast: plugins SHOULD cache any IDs they might need in performance critical situations. The return value 0 is reserved and indicates that an ID for that URI could not be created for whatever reason. Extensions MAY define more precisely what this means in a certain context, but in general plugins SHOULD handle this situation as gracefully as possible. However, hosts SHOULD NOT return 0 from this function in non-exceptional circumstances (e.g. the URI map SHOULD be dynamic). Hosts that statically support only a fixed set of URIs should not expect plugins to function correctly.

## Macro Definition Documentation

## ◆ LV2_URI_MAP_URI

#define LV2_URI_MAP_URI "http://lv2plug.in/ns/ext/uri-map"

http://lv2plug.in/ns/ext/uri-map

## ◆ LV2_URI_MAP_PREFIX

#define LV2_URI_MAP_PREFIX LV2_URI_MAP_URI "#"

http://lv2plug.in/ns/ext/uri-map#

## Variable Documentation

## ◆ LV2_URI_Map_Callback_Data

LV2_DEPRECATED typedef void* LV2_URI_Map_Callback_Data

Opaque pointer to host data.