Re: [fluid-dev] FluidSynth backend for SDL_mixer

[Pedro Lopez-Cabanillas]

On Thursday 07 October 2010, James Le Cuirot wrote:
> > Hmm, because they are private, that means that we are free to change
> > the implementation (and even remove the field) between FS versions.
> > I'm not sure I want to give up that freedom right away, what does the
> > rest of the list think here?
> > 
> > Also, I'm not exactly seeing why wrapping this in another struct
> > would be "a PITA", but you can also malloc another array next to the
> > event array containing the times if that works better for you. That
> > would also stop the overwriting problem you have.
> 
> I'm being very conservative with my memory management and backing out
> of a failed malloc could get messy with nested structs. Having a
> separate array works fine though. Should have thought of that! I've now
> made that change.

I don't know if you have already seen two examples using the sequencer 
(fluidsynth_metronome.c and fluidsynth_arpeggio.c) in the doc/ directory. One  
idea behind them is to keep the events, notes, patterns, the song, in whatever 
structure that comfortably represents (for your program) the list of 
timestamped events: the music, and then use new_fluid_event() and 
delete_fluid_event() just for the moment when you need to schedule the events 
to the sequencer.

> > I think you'll have to look at fluid_player_set_midi_tempo and do 
> > something similar, as you're doing your own midi file parser, that
> > is, combine PPQN with the MIDI_SET_TEMPO meta event.
> 
> I read up some more on SYSEX and found out what these meta events are.

SysEx is a real-time MIDI event (that may exists in a MIDI events stream, for 
instance in a wire connecting two MIDI devices) and Tempo is a SMF meta-event, 
that only exists inside MIDI files. There are also text and other types of 
meta events in SMF
http://home.roadrunner.com/~jgglatt/tech/midifile.htm
http://home.roadrunner.com/~jgglatt/tech/midispec/sysex.htm

The synth object doesn't do anything currently with sysex events, or with SMF  
meta-events.

> I now understand that the PPQN alone isn't enough even for the initial
> tempo so I need to handle this event. The problem is, as I mentioned
> before, there isn't a fluid_event function for tempo changes. I tried
> to work around this by dealing with it in a client callback but when I
> call fluid_sequencer_set_time_scale inside the callback, the game
> crashes with this horrific error.

This looks like a sensible design, scheduling a timer event (using the 
functions fluid_event_timer() and fluid_event_set_dest() with a client 
destination handler) for each tempo change in the MIDI file. Each timer event 
shall trigger the client callback, which in turn should call to the 
fluid_sequencer_set_time_scale() function corresponding to the new tempo. If 
this call crashes, there is a bug somewhere and we need to investigate. It 
would be nice (and easier) to have also a META sequencer event type to deal 
with these issues.

Regards,
Pedro