Help planning structure of randomly changing MIDI loop

[Adam Price]

I am playing around with the HeadFirst Beatbox. I have an idea for a modification, but my attempts at implementing have been unsuccessful (and as I get closer and closer I feel more and more like I am doing it wrong).

Without unnecessary detail, the program presents an GUI for designing a Midi sequence. There is a button to the side that causes a sequence to be built and started in a loop (buildTrackAndStart()) and another that interrupts the playing beat( via sequencer.stop();)

What I would like is for the sequence to randomly change every time through the loop. I tried the follwing setup, which failed miserably:
buildTrackAndStart() runs, then calls a copy of itself, buildTrackAndStartover() which in turn calls back to buildTrackAndStart() I threw in an appropriate snippet to make the random changes in each of the methods

The trouble is that the sequences never allow each other to finish. They interrupt each other on the first note over and over.

My nexy thought is to add a Midievent to the end of each sequence which will itself call the other buildTrackAnd*() This will be a little bit of a pain (because I don't know how to do it yet) so I wonder if I am going in the right direction anyway. Is there a better method for doing this?

Any thoughts appreciated...
-Adam
[ December 13, 2005: Message edited by: Adam Price ]

[Junilu Lacar]

Adam, post some code snippets so we have a better idea of what's going on. From what little I can glean though, I don't think you should be calling the method recursively:

buildTrackAndStart() runs, then calls a copy of itself, buildTrackAndStartover() which in turn calls back to buildTrackAndStart()

This is an example of indirect recursion.

[Adam Price]

public void buildTrackAndStart() {

int[] trackList = null;
sequencer.setTempoInBPM(BPM);
sequence.deleteTrack(track);


track = sequence.createTrack();

for (int i = 0; i < INSTRUMENT_COUNT; i++) {
trackList = new int[BEAT_COUNT];
int key = instruments[i];
for (int j = 0; j < BEAT_COUNT; j++) {

JCheckBox jc = (JCheckBox) checkboxList.get(j
+ (BEAT_COUNT * i));
if (jc.isSelected()) {
trackList[j] = key;
} else {
trackList[j] = 0;
}
}

makeTracks(trackList);
track.add(makeEvent(176, 1, 127, 0, BEAT_COUNT));
}
try {
sequencer.setSequence(sequence);
sequencer.setLoopCount(2);
                   //sequencer.setLoopCount(sequencer.LOOP_CONTINUOUSLY);   (commented out because I don't want each midi sequence to loop ad nauseum.
sequencer.start();
} catch (Exception e) {
e.printStackTrace();
}

}//end buildTrackAndStart

This scans a 16x16 grid of checkboxes to see what midi instruments should fire (rows) on what beats (columns). I want to randomly tweak it each time through the loop with :

int ranFlipper = (int) (Math.random() * BEAT_COUNT * INSTRUMENT_COUNT);
if((checkboxList.get(ranFlipper).isSelected() ==false)&& Math.random()>.25)                           
                       {checkboxList.get(ranFlipper).setSelected(true);}
else {checkboxList.get(ranFlipper).setSelected(false);}

The tweak works fine - the trouble is finding a way to have the method keep generating and playing sequences incorporating the tweak (at least until I poke the stop button, which calls the method:

public class MyStopListener implements ActionListener {
public void actionPerformed(ActionEvent a) {
sequencer.stop();
}
}

for the full code, before my attempts to add this random loop, see my other thread Modified Head First Beatbox
[ December 13, 2005: Message edited by: Adam Price ]

[Junilu Lacar]

Adam, I don't have any experience with the sound classes but it seems to me like you're going to have to bone up on threads. The sequencer has an isRunning() method that returns true if it's running a sequence. This suggests to me that it is spawning a thread that plays the sequence. I think you're going to have set up a loop to poll the sequencer to see if it's still running (it'd be nice if there was a way to just listen for a "loop done" event, wouldn't it?) and only build and start a new sequence after the current one completes running.

pseudocode:

 
  loop:
 
     set up sequencer
     start sequencer
 
     while sequencer is running 
        do nothing (just wait for it to stop running)
 
     if user clicked "stop"
        break out of loop
     else 
        continue loop

[ December 14, 2005: Message edited by: Junilu Lacar ]

[Adam Price]

Originally posted by Junilu Lacar:

 
  loop:
 
     set up sequencer
     start sequencer
 
     while sequencer is running 
        do nothing (just wait for it to stop running)
 
     if user clicked "stop"
        break out of loop
     else 
        continue loop

ok - here's my new flow:

set boolean pausedState to false  (the stop button now toggles the paused state)
 
buildTrackAndStart:
    if pausedState=false
            make a new loop
            playLoop()
     else break
playLoop
   start the sequencer playing
   while sequencer.isRunning() DO NOTHING   <----??
   buildTrackAndStart

It works in the barest sense - it plays the loop with random changes now and then, just as it should. Three problems though:

1. The grid of checkboxes is never redrawn to show which ones have been checked. I have tried forcing a repaint of the panel they are in and of the whole frame - no luck
2. The stop button doesn't work - it toggles fine before I start the sequence, but once it gets going, it can't seem to get a toggle in edgewise.
3. I am new to OOP, so maybe my expectations are wrong, but this flow feels very procedural, particularly the part where I make it wait by doing nothing while the sequence is running. Is this flow inf good style, or is a a gross hack?

Thanks for input!

[Junilu Lacar]

The empty while loop is eating up all the clock cycles and not letting the buttons get in on the action. Like I said before, you're going to have to bone up on threads: http://javaalmanac.com/egs/java.lang/PauseThread.html

As for being hacky or non-OOP, thinking in terms objects is just a way of abstracting and organizing a solution to a problem. At some point, however, you're going to have to go down to a level where all you have left is a sequence of commands that need to be executed by the computer. After all, statements like the for-loop, if-then-else, and while statements all come from procedural-type languages, don't they?