Draw is looping but an inner loop is causing it not to render to the screen

Programming Questions

kevdean

Draw is looping but an inner loop is causing it not to render to the screen

in Programming Questions • 5 months ago

Hi, I have a strange problem related to rendering that I'm hoping someone will understand. I have a simple application that draws the circumference of a circle one step at a time in sync with beat data from Echonest.

In order to sync the drawing with each beat, I put a While loop inside Draw that retrieves that next beat from the Echonest data and then keeps looping until the song reaches a short window of time around that beat (i.e., within 13ms before or after it). I then draw the next circle segment, the While loop exits, and Draw completes. The problem is that, even though the code to draw the circle segment is getting performed and even though Draw is in fact looping properly, nothing is getting rendered. I just get a gray viewport. And I know that the While loop is causing the problem because, when I remove the condition that causes the While loop to keep looping until we hit the right window of time, it renders just fine. Moreover, if I leave that condition in, but drop my frame rate down to 3 or lower, then it renders fine as well.

So it seems that the inner loop is causing some sort of havoc with Processing. Does anyone have an idea of what could be happening and what a good solution is? Similarly, does anyone know of a better way to sync music and an animation (I tried doing it real-time with Minim, but I was struggling to get good results, particularly due to apparent latency).

Thanks,

Kevin

while (_currBeatFndInd == false && _currBeatIdx < _beats.length) {

int startTmMsNbr = ( int)(Float.parseFloat( _beats[ _currBeatIdx].get( "start").toString()) * 1000);

if (startTmMsNbr >= _player.position() - MAX_LATENCY_MS_NBR) {
_msToNextBeatNbr = abs(startTmMsNbr - _player.position());

      if (_msToNextBeatNbr <= MAX_LATENCY_MS_NBR ) {
      //if (true) {
            circles.get(0).update();
            println( _currBeatIdx + " drawn");
            _currBeatFndInd = true ;
            _currBeatIdx ++;
      } else {
            // println(_currBeatIdx + "  " + _msToNextBeatNbr);
      }
} else {
      _currBeatIdx ++;
}

}

Replies(3)

Chrisir

Re: Draw is looping but an inner loop is causing it not to render to the screen

5 months ago

hello,

the screen is only updated once at the end of draw.

That means draw() adds up all circle segments but puts them on the screen only at the very end of draw().

That means during while nothing changes.

without understanding the code I therefore suggest to get rid of while and use the looping functionality of draw itself. Thus you should see a change on the screen.

[not tested]

Greetings, Chrisir

if (_currBeatFndInd == false && _currBeatIdx < _beats.length) {
int startTmMsNbr = ( int)(Float.parseFloat( _beats[ _currBeatIdx].get( "start").toString()) * 1000);
if (startTmMsNbr >= _player.position() - MAX_LATENCY_MS_NBR) {
_msToNextBeatNbr = abs(startTmMsNbr - _player.position());
      if (_msToNextBeatNbr <= MAX_LATENCY_MS_NBR ) {
      //if (true) {
            circles.get(0).update();
            println( _currBeatIdx + " drawn");
            _currBeatFndInd = true ;
            _currBeatIdx ++;
      } else {
            // println(_currBeatIdx + "  " + _msToNextBeatNbr);
      }
} else {
      _currBeatIdx ++;
} // else
} // if

kevdean

Re: Draw is looping but an inner loop is causing it not to render to the screen

5 months ago

Thanks for the reply, Chrisir. Yeah, I wound up just getting rid of the While and depending strictly on the Draw loop, just as you suggested. I could never figure out why the While was causing a problem. Relying on the Draw loop works, but it's unsatisfying because it does introduce unnecessary overhead. Essentially what I was trying to do was to complete the Draw function only when I actually wanted something new drawn to the screen based on tight syncing with the beat. It seemed like creating my own loop was the best way to create that close syncing (rather than putting the thread to sleep, for instance), but for some reason Processing doesn't seem to like that. I may investigate more in the future, but for now the Draw loop is sufficient.

Thanks again!