20 Dec
2016
20 Dec
'16
5:30 a.m.
On 20.12.2016 12:09, ROBERT WOLF wrote:
What exactly is the difference between
*jack_midi_event_reserve* and
*jack_midi_event_write* ?
In particular, if I call *jack_midi_event_write*, does it actually copy the data
from the buffer, which I provide?
For a simple MIDI message
const size_t sz = 3;
const uint8_t src [sz] = {0x90, 0x2f, 0x7f};
think of jack_midi_event_write as a convenience wrapper around
jack_midi_event_reserve and memcpy
uint8_t *dst = jack_midi_event_reserve(client, 0, sz);
if(dst)
memcpy(dst, src, sz);
else
; // no space left on buffer
which is equivalent to
if(jack_midi_event_write(client, 0, src, sz) != 0)
; // no space left on buffer
Or does it use that same buffer.
Another question is how can I send midi events generated from GUI, (which does
not run in the audio callback)?
My guess is to cache them somewhere and transmit them inside the callback?
Am I guessing correctly?
The common practice is to use lock-free single-reader/single-writer ring buffers
to exchange data between worker/GUI and audio threads.
JACK readily ships its own implementation of such a structure [1].
[1] http://jackaudio.org/api/ringbuffer_8h.html