Mixer buses

since 0.2.0 Simulation, audio and XR

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A settings screen usually has a music slider and an effects slider, and both sit under a master. AudioBus names the groups and Mixer holds what each one is turned to, read every frame so moving a slider is heard immediately.

Step 1: A mixer #

_mixer = Mixer();

Step 2: Set some volumes #

setVolume takes a bus and a level from 0 to 1.

void _apply() {
  _mixer
    ..setVolume(AudioBus.music, musicVolume)
    ..setVolume(AudioBus.master, masterVolume);
}

Step 3: Read the gain a sound actually plays at #

gainFor multiplies a bus's own volume by the master, since master is not a special case, only another bus everything is also on.

final musicGain = _mixer.gainFor(AudioBus.music);
final sfxGain = _mixer.gainFor(AudioBus.sfx);

AudioBus.sfx is never configured on this page, and gainFor still answers 1.0 for it: an unset bus is full rather than silent, so a game that forgets to configure one is still heard.

Step 4: Watch the levels #

Three bars stand on the page: the blue one is music as it is actually heard, after the master; the yellow one is sfx, which nobody configured; the purple one is the master itself. Slide Music volume and only the blue one moves. Slide Master volume and the blue and the yellow both follow it, because every bus is multiplied by the master; the yellow one otherwise stays at full, since an unset bus does until a game turns it down.

final musicGain = _mixer.gainFor(AudioBus.music);
final sfxGain = _mixer.gainFor(AudioBus.sfx);