PulpCore music playback - loop sound and animate volume

Question

I have been experimenting with PulpCore, trying to create my own tower defence game (not-playable yet), and I am enjoying it very much I ran into a problem that I can't quite figure out. I extended PulpCore with the JOrbis thing to allow OGG files to be played. Works fine. However, pulpCore seems to have a problem with looping the sound WHILE animating the volume level. I tried this with wav file too, to make sure it isn't jOrbis that breaks it. The code is like this:

Sound bgMusic = Sound.load("music/music.ogg");
Playback musicPlayback;
...

musicVolume = new Fixed(0.75);
musicPlayback = bgMusic.loop(musicVolume);
//TODO figure out why it's NOT looping when volume is animated
//  musicVolume.animate(0, musicVolume.get(), FADE_IN_TIME);

This code, for as long as the last line is commented out, plays the music.ogg again and again in an endless loop (which I can stop by calling stop on the Playback object returned from loop(). However, I would like the music to fade in smoothly, so following the advice of the PulpCore API docs, I added the last line which will create the fade-in but the music will only play once and then stop. I wonder why is that? Here is a bit of the documentation:

Playback pulpcore.sound.Sound.loop(Fixed level)

Loops this sound clip with the specified volume level (0.0 to 1.0). The level may have a property animation attached.

Parameters: level

Returns: a Playback object for this unique sound playback (one Sound can have many simultaneous Playback objects) or null if the sound could not be played.

So what could be the problem? I repeat, with the last line, the sound fades in but doesn't loop, without it it loops but starts with the specified 0.75 volume level. Why can't I animate the volume of the looped music playback? What am I doing wrong? Anyone has any experience with pulpCore and has come across this problem? Anyone could please download PulpCore and try to loop music which fades-in (out)?

note: I need to keep a reference to the Playback object returned so I can kill music later.

Answer 1

Finally I managed to get an explanation and a simple work-around for this issue from the pulp core author. So here it is:

It is a PulpCore bug. When the output volume is zero, the sound player stops looping the sound.

To work around it, animate from a value that is not zero, like this:

musicVolume.animate(0.0001, 1, FADE_IN_TIME); 

Link to this on pulpcore Google groups

Answer 2

If the animate method only sets the option, it can work unpredictably - try switching this line with the loop itself, so the animation applies first.

Answer 3

Can you animate the volume on an unlooped playback, and then, at the end of that playback, start the loop at the fixed level?