Killer Game Programming in Java

Storing Midi Information

A MidiInfo object holds a single MIDI sequence and a reference to the sequencer created in MidisLoader. This allows it to play, stop, pause, and resume a clip, and make it loop.

The constructor is passed the sequence's name, filename, and the sequencer reference, and then it loads the sequence using MidiSystem.getSequence(). A sequence is played by loading it into the sequencer and starting the sequence:

    public void play(boolean toLoop)
    {
      if ((sequencer != null) && (seq != null)) {
        try {
          sequencer.setSequence(seq);   // load sequence into sequencer
          sequencer.setTickPosition(0); // reset to the start
          isLooping = toLoop;
          sequencer.start();            // play it
        }
        catch (InvalidMidiDataException e) {
          System.out.println("Invalid midi file: " + filename);
        }
      }
    }

The Sequencer class has several loop() methods, but they aren't used here. A similar coding technique is employed as in ClipInfo: A global isLooping Boolean is set to true and employed later by tryLooping(). This permits us to trigger a callback in a watcher at the end of each iteration.

Stopping Sequences

Stopping a sequence with Sequencer.stop() causes it to stop at its current position. More importantly, no metaevent is generated unless the stopping coincides with the end of the track. In order to generate an event, my stop() method "winds" the sequence to its end:

 public void stop() { if ((sequencer != null) && (seq != null)) { isLooping = false; if (!sequencer.isRunning()) // the sequence may be paused sequencer.start(); ...