source/includes/lv2/lv2-miditype.h

   1 /****************************************************************************
   2
   3     lv2-miditype.h - header file for using MIDI in LV2 plugins
   4
   5     Copyright (C) 2006  Lars Luthman <lars.luthman@gmail.com>
   6
   7     This program is free software; you can redistribute it and/or modify
   8     it under the terms of the GNU Lesser General Public License as published by
   9     the Free Software Foundation; either version 2 of the License, or
  10     (at your option) any later version.
  11
  12     This program is distributed in the hope that it will be useful,
  13     but WITHOUT ANY WARRANTY; without even the implied warranty of
  14     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15     GNU Lesser General Public License for more details.
  16
  17     You should have received a copy of the GNU Lesser General Public License
  18     along with this program; if not, write to the Free Software
  19     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 01222-1307  USA
  20
  21 ****************************************************************************/
  22
  23 #ifndef LV2_MIDITYPE_H
  24 #define LV2_MIDITYPE_H
  25
  26 #ifdef __cplusplus
  27 extern "C" {
  28 #endif
  29
  30 /** This data structure is used to contain the MIDI events for one run()
  31     cycle. The port buffer for a LV2 port that has the datatype
  32     <http://ll-plugins.nongnu.org/lv2/ext/miditype> should be a pointer
  33     to an instance of this struct.
  34
  35     To store two Note On events on MIDI channel 0 in a buffer, with timestamps
  36     12 and 35.5, you could use something like this code (assuming that
  37     midi_data is a variable of type LV2_MIDI):
  38     @code
  39
  40       size_t buffer_offset = 0;
  41       *(double*)(midi_data->data + buffer_offset) = 12;
  42       buffer_offset += sizeof(double);
  43       *(size_t*)(midi_data->data + buffer_offset) = 3;
  44       buffer_offset += sizeof(size_t);
  45       midi_data->data[buffer_offset++] = 0x90;
  46       midi_data->data[buffer_offset++] = 0x48;
  47       midi_data->data[buffer_offset++] = 0x64;
  48       ++midi_data->event_count;
  49
  50       *(double*)(midi_data->data + buffer_offset) = 35.5;
  51       buffer_offset += sizeof(double);
  52       *(size_t*)(midi_data->data + buffer_offset) = 3;
  53       buffer_offset += sizeof(size_t);
  54       midi_data->data[buffer_offset++] = 0x90;
  55       midi_data->data[buffer_offset++] = 0x55;
  56       midi_data->data[buffer_offset++] = 0x64;
  57       ++midi_data->event_count;
  58
  59       midi_data->size = buffer_offset;
  60
  61     @endcode
  62
  63     This would be done by the host in the case of an input port, and by the
  64     plugin in the case of an output port. Whoever is writing events to the
  65     buffer must also take care not to exceed the capacity of the data buffer.
  66
  67     To read events from a buffer, you could do something like this:
  68     @code
  69
  70       size_t buffer_offset = 0;
  71       uint32_t i;
  72       for (i = 0; i < midi_data->event_count; ++i) {
  73         double timestamp = *(double*)(midi_data->data + buffer_offset);
  74         buffer_offset += sizeof(double);
  75         size_t size = *(size_t*)(midi_data->data + buffer_offset);
  76         buffer_offset += sizeof(size_t);
  77         do_something_with_event(timestamp, size,
  78                                 midi_data->data + buffer_offset);
  79         buffer_offset += size;
  80       }
  81
  82     @endcode
  83 */
  84 typedef struct {
  85
  86   /** The number of MIDI events in the data buffer.
  87       INPUT PORTS: It's the host's responsibility to set this field to the
  88       number of MIDI events contained in the data buffer before calling the
  89       plugin's run() function. The plugin may not change this field.
  90       OUTPUT PORTS: It's the plugin's responsibility to set this field to the
  91       number of MIDI events it has stored in the data buffer before returning
  92       from the run() function. Any initial value should be ignored by the
  93       plugin.
  94   */
  95   uint32_t  event_count;
  96
  97   /** The size of the data buffer in bytes. It is set by the host and may not
  98       be changed by the plugin. The host is allowed to change this between
  99       run() calls.
 100   */
 101   uint32_t  capacity;
 102
 103   /** The size of the initial part of the data buffer that actually contains
 104       data.
 105       INPUT PORTS: It's the host's responsibility to set this field to the
 106       number of bytes used by all MIDI events it has written to the buffer
 107       (including timestamps and size fields) before calling the plugin's
 108       run() function. The plugin may not change this field.
 109       OUTPUT PORTS: It's the plugin's responsibility to set this field to
 110       the number of bytes used by all MIDI events it has written to the
 111       buffer (including timestamps and size fields) before returning from
 112       the run() function. Any initial value should be ignored by the plugin.
 113   */
 114   uint32_t  size;
 115
 116   /** The data buffer that is used to store MIDI events. The events are packed
 117       after each other, and the format of each event is as follows:
 118
 119       First there is a timestamp, which should have the type "double",
 120       i.e. have the same bit size as a double and the same bit layout as a
 121       double (whatever that is on the current platform). This timestamp gives
 122       the offset from the beginning of the current cycle, in frames, that
 123       the MIDI event occurs on. It must be strictly smaller than the 'nframes'
 124       parameter to the current run() call. The MIDI events in the buffer must
 125       be ordered by their timestamp, e.g. an event with a timestamp of 123.23
 126       must be stored after an event with a timestamp of 65.0.
 127
 128       The second part of the event is a size field, which should have the type
 129       "size_t" (as defined in the standard C header stddef.h). It should
 130       contain the size of the MIDI data for this event, i.e. the number of
 131       bytes used to store the actual MIDI event. The bytes used by the
 132       timestamp and the size field should not be counted.
 133
 134       The third part of the event is the actual MIDI data. There are some
 135       requirements that must be followed:
 136
 137       * Running status is not allowed. Every event must have its own status
 138         byte.
 139       * Note On events with velocity 0 are not allowed. These events are
 140         equivalent to Note Off in standard MIDI streams, but in order to make
 141         plugins and hosts easier to write, as well as more efficient, only
 142         proper Note Off events are allowed as Note Off.
 143       * "Realtime events" (status bytes 0xF8 to 0xFF) are allowed, but may not
 144         occur inside other events like they are allowed to in hardware MIDI
 145         streams.
 146       * All events must be fully contained in a single data buffer, i.e. events
 147         may not "wrap around" by storing the first few bytes in one buffer and
 148         then wait for the next run() call to store the rest of the event. If
 149         there isn't enough space in the current data buffer to store an event,
 150         the event will either have to wait until next run() call, be ignored,
 151         or compensated for in some more clever way.
 152       * All events must be valid MIDI events. This means for example that
 153         only the first byte in each event (the status byte) may have the eighth
 154         bit set, that Note On and Note Off events are always 3 bytes long etc.
 155         The MIDI writer (host or plugin) is responsible for writing valid MIDI
 156         events to the buffer, and the MIDI reader (plugin or host) can assume
 157         that all events are valid.
 158
 159       On a platform where double is 8 bytes and size_t is 4 bytes, the data
 160       buffer layout for a 3-byte event followed by a 4-byte event may look
 161       something like this:
 162       _______________________________________________________________
 163       | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | ...
 164       |TIMESTAMP 1    |SIZE 1 |DATA |TIMESTAMP 2    |SIZE 2 |DATA   | ...
 165
 166   */
 167   unsigned char* data;
 168
 169 } LV2_MIDI;
 170
 171 #ifdef __cplusplus
 172 }  /* extern "C" */
 173 #endif
 174
 175 #endif