preload method

@override Future<void> preload(String asset)

Reads an asset so that start does not have to wait.

Implementation

@override
Future<void> preload(String asset) async {
  if (_sources.containsKey(asset)) return;
  final AudioSource source;
  try {
    // The bytes first and the source from them, rather than `loadAsset`:
    // the file's sample rate is in its header, and the filter below has to
    // know it. See `cutoff.dart`.
    final bytes = (await rootBundle.load(asset)).buffer.asUint8List();
    _sampleRates[asset] = wavSampleRate(bytes) ?? _kAssumedSampleRate;
    source = await _soloud.loadMem(asset, bytes);
  } catch (error) {
    // A missing sound leaves the game silent in one place rather than
    // stopping it. Losing a footstep should not cost the play-test — but it
    // is worth saying out loud, because silence is what a sound that works
    // and a sound that failed to decode look like from the outside.
    _failed.add(asset);
    onIssue(Issue('could not load "$asset": $error'));
    return;
  }
  _sources[asset] = source;
  // A low-pass on every source, open all the way, so a voice heard through
  // a wall can be dulled by moving its cutoff rather than by starting a
  // filter mid-sound — which is a click. Per source rather than global,
  // because a global filter has one cutoff for every voice at once, and a
  // torch behind the door and a torch beside you are not the same torch.
  try {
    final filter = source.filters.biquadFilter;
    if (!filter.isActive) filter.activate();
    filter.type().value = _kLowPass;
    // What a voice starts with before [start] sets its own: open for any
    // speed down to half, so no voice ever begins past its Nyquist.
    filter.frequency().value = openCutoff(
      sampleRate: _sampleRates[asset]!,
      rate: 0.5,
    );
  } catch (error) {
    if (!_filterRefused) {
      _filterRefused = true;
      onIssue(
        Issue(
          'no low-pass filter on this platform, walls only quieten: $error',
        ),
      );
    }
  }
}