libs/ardour/lv2ext/lv2_uri_map.h

   1 /* lv2_uri_map.h - C header file for the LV2 URI Map extension.
   2  *
   3  * Copyright (C) 2008 David Robillard <d@drobilla.net>
   4  *
   5  * This header is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU Lesser General Public License as published
   7  * by the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This header is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  13  * License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public License
  16  * along with this header; if not, write to the Free Software Foundation,
  17  * Inc., 59 Temple Place, Suite 330, Boston, MA 01222-1307 USA
  18  */
  19
  20 #ifndef LV2_URI_MAP_H
  21 #define LV2_URI_MAP_H
  22
  23 #define LV2_URI_MAP_URI "http://lv2plug.in/ns/ext/uri-map"
  24
  25 #include <stdint.h>
  26
  27 /** @file
  28  * This header defines the LV2 URI Map extension with the URI
  29  * <http://lv2plug.in/ns/ext/uri-map> (preferred prefix 'lv2urimap').
  30  *
  31  * This extension defines a simple mechanism for plugins to map URIs to
  32  * integers, usually for performance reasons (e.g. processing events
  33  * typed by URIs in real time).  The expected use case is for plugins to
  34  * map URIs to integers for things they 'understand' at instantiation time,
  35  * and store those values for use in the audio thread without doing any string
  36  * comparison.  This allows the extensibility of RDF with the performance of
  37  * integers (or centrally defined enumerations).
  38  */
  39
  40
  41 /** Opaque pointer to host data. */
  42 typedef void* LV2_URI_Map_Callback_Data;
  43
  44
  45 /** The data field of the LV2_Feature for this extension.
  46  *
  47  * To support this feature the host must pass an LV2_Feature struct to the
  48  * plugin's instantiate method with URI "http://lv2plug.in/ns/ext/uri-map"
  49  * and data pointed to an instance of this struct.
  50  */
  51 typedef struct {
  52
  53         /** Opaque pointer to host data.
  54          *
  55          * The plugin MUST pass this to any call to functions in this struct.
  56          * Otherwise, it must not be interpreted in any way.
  57          */
  58         LV2_URI_Map_Callback_Data callback_data;
  59
  60         /** Get the numeric ID of a URI from the host.
  61          *
  62          * @param callback_data Must be the callback_data member of this struct.
  63          * @param map The 'context' of this URI.  Certain extensions may define a
  64          *        URI that must be passed here with certain restrictions on the
  65          *        return value (e.g. limited range).  This value may be NULL if
  66          *        the plugin needs an ID for a URI in general.
  67          * @param uri The URI to be mapped to an integer ID.
  68          *
  69          * This function is referentially transparent - any number of calls with
  70          * the same arguments is guaranteed to return the same value over the life
  71          * of a plugin instance (though the same URI may return different values
  72          * with a different map parameter).  However, this function is not
  73          * necessarily very fast: plugins should cache any IDs they might need in
  74          * performance critical situations.
  75          * The return value 0 is reserved and means an ID for that URI could not
  76          * be created for whatever reason.  Extensions may define more precisely
  77          * what this means, but in general plugins should gracefully handle 0
  78          * and consider whatever they wanted the URI for "unsupported".
  79          */
  80         uint32_t (*uri_to_id)(LV2_URI_Map_Callback_Data callback_data,
  81                               const char*               map,
  82                               const char*               uri);
  83
  84 } LV2_URI_Map_Feature;
  85
  86
  87 #endif // LV2_URI_MAP_H
  88