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
  27 /** This data structure is used to contain the MIDI events for one run()
  28     cycle. The port buffer for a LV2 port that has the datatype
  29     <http://ll-plugins.nongnu.org/lv2/ext/miditype> should be a pointer
  30     to an instance of this struct.
  31
  32     To store two Note On events on MIDI channel 0 in a buffer, with timestamps
  33     12 and 35.5, you could use something like this code (assuming that
  34     midi_data is a variable of type LV2_MIDI):
  35     @code
  36
  37       size_t buffer_offset = 0;
  38       *(double*)(midi_data->data + buffer_offset) = 12;
  39       buffer_offset += sizeof(double);
  40       *(size_t*)(midi_data->data + buffer_offset) = 3;
  41       buffer_offset += sizeof(size_t);
  42       midi_data->data[buffer_offset++] = 0x90;
  43       midi_data->data[buffer_offset++] = 0x48;
  44       midi_data->data[buffer_offset++] = 0x64;
  45       ++midi_data->event_count;
  46
  47       *(double*)(midi_data->data + buffer_offset) = 35.5;
  48       buffer_offset += sizeof(double);
  49       *(size_t*)(midi_data->data + buffer_offset) = 3;
  50       buffer_offset += sizeof(size_t);
  51       midi_data->data[buffer_offset++] = 0x90;
  52       midi_data->data[buffer_offset++] = 0x55;
  53       midi_data->data[buffer_offset++] = 0x64;
  54       ++midi_data->event_count;
  55
  56       midi_data->size = buffer_offset;
  57
  58     @endcode
  59
  60     This would be done by the host in the case of an input port, and by the
  61     plugin in the case of an output port. Whoever is writing events to the
  62     buffer must also take care not to exceed the capacity of the data buffer.
  63
  64     To read events from a buffer, you could do something like this:
  65     @code
  66
  67       size_t buffer_offset = 0;
  68       uint32_t i;
  69       for (i = 0; i < midi_data->event_count; ++i) {
  70         double timestamp = *(double*)(midi_data->data + buffer_offset);
  71         buffer_offset += sizeof(double);
  72         size_t size = *(size_t*)(midi_data->data + buffer_offset);
  73         buffer_offset += sizeof(size_t);
  74         do_something_with_event(timestamp, size,
  75                                 midi_data->data + buffer_offset);
  76         buffer_offset += size;
  77       }
  78
  79     @endcode
  80 */
  81 typedef struct {
  82
  83   /** The number of MIDI events in the data buffer.
  84       INPUT PORTS: It's the host's responsibility to set this field to the
  85       number of MIDI events contained in the data buffer before calling the
  86       plugin's run() function. The plugin may not change this field.
  87       OUTPUT PORTS: It's the plugin's responsibility to set this field to the
  88       number of MIDI events it has stored in the data buffer before returning
  89       from the run() function. Any initial value should be ignored by the
  90       plugin.
  91   */
  92   uint32_t  event_count;
  93
  94   /** The size of the data buffer in bytes. It is set by the host and may not
  95       be changed by the plugin. The host is allowed to change this between
  96       run() calls.
  97   */
  98   uint32_t  capacity;
  99
 100   /** The size of the initial part of the data buffer that actually contains
 101       data.
 102       INPUT PORTS: It's the host's responsibility to set this field to the
 103       number of bytes used by all MIDI events it has written to the buffer
 104       (including timestamps and size fields) before calling the plugin's
 105       run() function. The plugin may not change this field.
 106       OUTPUT PORTS: It's the plugin's responsibility to set this field to
 107       the number of bytes used by all MIDI events it has written to the
 108       buffer (including timestamps and size fields) before returning from
 109       the run() function. Any initial value should be ignored by the plugin.
 110   */
 111   uint32_t  size;
 112
 113   /** The data buffer that is used to store MIDI events. The events are packed
 114       after each other, and the format of each event is as follows:
 115
 116       First there is a timestamp, which should have the type "double",
 117       i.e. have the same bit size as a double and the same bit layout as a
 118       double (whatever that is on the current platform). This timestamp gives
 119       the offset from the beginning of the current cycle, in frames, that
 120       the MIDI event occurs on. It must be strictly smaller than the 'nframes'
 121       parameter to the current run() call. The MIDI events in the buffer must
 122       be ordered by their timestamp, e.g. an event with a timestamp of 123.23
 123       must be stored after an event with a timestamp of 65.0.
 124
 125       The second part of the event is a size field, which should have the type
 126       "size_t" (as defined in the standard C header stddef.h). It should
 127       contain the size of the MIDI data for this event, i.e. the number of
 128       bytes used to store the actual MIDI event. The bytes used by the
 129       timestamp and the size field should not be counted.
 130
 131       The third part of the event is the actual MIDI data. There are some
 132       requirements that must be followed:
 133
 134       * Running status is not allowed. Every event must have its own status
 135         byte.
 136       * Note On events with velocity 0 are not allowed. These events are
 137         equivalent to Note Off in standard MIDI streams, but in order to make
 138         plugins and hosts easier to write, as well as more efficient, only
 139         proper Note Off events are allowed as Note Off.
 140       * "Realtime events" (status bytes 0xF8 to 0xFF) are allowed, but may not
 141         occur inside other events like they are allowed to in hardware MIDI
 142         streams.
 143       * All events must be fully contained in a single data buffer, i.e. events
 144         may not "wrap around" by storing the first few bytes in one buffer and
 145         then wait for the next run() call to store the rest of the event. If
 146         there isn't enough space in the current data buffer to store an event,
 147         the event will either have to wait until next run() call, be ignored,
 148         or compensated for in some more clever way.
 149       * All events must be valid MIDI events. This means for example that
 150         only the first byte in each event (the status byte) may have the eighth
 151         bit set, that Note On and Note Off events are always 3 bytes long etc.
 152         The MIDI writer (host or plugin) is responsible for writing valid MIDI
 153         events to the buffer, and the MIDI reader (plugin or host) can assume
 154         that all events are valid.
 155
 156       On a platform where double is 8 bytes and size_t is 4 bytes, the data
 157       buffer layout for a 3-byte event followed by a 4-byte event may look
 158       something like this:
 159       _______________________________________________________________
 160       | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | ...
 161       |TIMESTAMP 1    |SIZE 1 |DATA |TIMESTAMP 2    |SIZE 2 |DATA   | ...
 162
 163   */
 164   unsigned char* data;
 165
 166 } LV2_MIDI;
 167
 168
 169
 170 #endif