[Solved]: Qt and asynchronous c++ midi library

mrscope

Hi guys,

i'm looking for develop a simple app with a third part c++ library the libjdkmidi (http://www.jdkoftinoff.com/main/Free_Projects/C++_MIDI_Library/)

Now i'm studying an example of the library that play a midifile. It works well in a console app...

The problem (a common problem :-) is integrate it in GUI app.

I've this code :

@MIDIFileReadStreamFile rs ( "c:/temp/360.mid" );
MIDIMultiTrack tracks ( 64 );
MIDIFileReadMultiTrack track_loader ( &tracks );
MIDIFileRead reader ( &rs, &track_loader );
//MIDISequencerGUIEventNotifierText gui ( stdout );
MIDISequencer seq ( &tracks );
MIDIDriverWin32 driver ( 128 );
MIDIManager mgr ( &driver );
reader.Parse();
driver.StartTimer ( 20 );
driver.OpenMIDIOutPort ( MIDI_MAPPER );
seq.GoToZero();
mgr.SetSeq ( &seq );
mgr.SetTimeOffset ( timeGetTime() );
mgr.SeqPlay();
getchar();
mgr.SeqStop();@

now, the mgr.SeqPlay play the midifile and the getchar() function wait for an input allowing the mgr.SeqPlay to finish play the midifile.

obviously the getchar() freeze the GUI and i (for now) fix replacing it with
@ while (mgr.IsSeqPlay()) {qApp->processEvents();};@

The problem is it take a lot of CPU (50% on a dualcore) because the processEvents is a cpu intensive processment.

Can you give me a point of start about it? What i must use, thread ? QtConcurrent? and ... how ?

Thanks for your help!

Luca

Peleron

Make derived class of QRunnable
Reimplement method run() in your class:
@void run()
{
MIDIFileReadStreamFile rs ( "c:/temp/360.mid" );
MIDIMultiTrack tracks ( 64 );
MIDIFileReadMultiTrack track_loader ( &tracks );
MIDIFileRead reader ( &rs, &track_loader );
//MIDISequencerGUIEventNotifierText gui ( stdout );
MIDISequencer seq ( &tracks );
MIDIDriverWin32 driver ( 128 );
MIDIManager mgr ( &driver );
reader.Parse();
driver.StartTimer ( 20 );
driver.OpenMIDIOutPort ( MIDI_MAPPER );
seq.GoToZero();
mgr.SetSeq ( &seq );
mgr.SetTimeOffset ( timeGetTime() );
mgr.SeqPlay();
}@
Its enough if calling SeqStop() procedure not necessary.
Somewhere call this method via start()

mrscope

@Peleron: thanks...

i've tried this (as few examples found on the network)

@PlayerRunnable *pl= new PlayerRunnable ();
pl->setAutoDelete(false);
QThreadPool::globalInstance()->start(pl);@

after reimplemented method run() as you wrote, but it doesn't work. I think it quit after the mgr.SeqPlay

mrscope

[quote author="LuckyLiuk" date="1320946506"]@Peleron: thanks...

but it doesn't work.

[/quote]

The player doesn't sound

mrscope

i've fixed it with:
@ QEventLoop q;
mgr.SeqPlay();
q.exec();@

but not sure if it's correct or can be give me problems . What do you think ?

giesbert

For me, it looks like midi playback is already done in a thread. so I would make MIDIManager a member of my class, call mgr.SeqPlay(); and then return from the slot.
So no need of process event, qrunnable, a thread or whatever.

mrscope

@Gerolf

Hmmm i think you have the reason. I'll try . Tnx

mrscope

It works! Thanks.

SherifOmran

Hi LuckyLiuk,

I have the same problem, trying to play a midi file but it does not work . I would appreciate if you share you class .

SherifOmran

Hi LuckyLiuk,

I have the same problem, trying to play a midi file but it does not work . I would appreciate if you share you class .