Expose the actively played beats through new event

[Danielku15]

As discussed here it is currently not possible outside of alphaTab. alphaTab keeps properly track of the active beats for highlighting purposes but an integrator cannot obtain this list for any custom purposes.

But the playedBeatChanged is only called with the beat which is used for cursor placement.

The idea would be to add a activeBeatsChanged which is always called with the full list of beats which are currently considered active. Integrators can then use this list for any custom purposes like updating fretboards or track lists with custom indicators.

[Danielku15]

chrome_VusSrNSOuM.mp4

Ping @marriusco @circinusX1

Here a demo of the upcoming feature. The text is generated using a code like

    const activeBeatsDisplay = document.querySelector('#activeBeats');
    at.activeBeatsChanged.on(function(args) {
        activeBeatsDisplay.innerText = args.activeBeats
            .map(b => `${b.voice.bar.staff.track.name} - Bar ${b.voice.bar.index} - Beat at ${b.displayStart}` )
            .join('\n');
    });

A new event activeBeatsChanged is added where the list of active beats is passed into the handlers. This list is independent from the rendering as you can see from the output. The sorting is not deterministic due to the reason how this list is computed during audio generation, but with a Map any application could optimize the handling of added/removed beats accordingly.

Does this fit your needs?

[Danielku15]

And a (ugly sounding) demo with multiple voices.

chrome_q8gTiLUOWp.mp4