func update() {
lock.Lock()
defer lock.Unlock()
_, write, err := dsound.GetPlayAndWriteCursors()
if err != nil {
lastError = err
return
}
if write != writeCursor {
var delta uint
if write > writeCursor {
delta = write - writeCursor
} else {
// wrap-around happened in DirectSound's ring buffer
delta = write + dsound.BufferSize() - writeCursor
}
advanceSoundsByBytes(int(delta))
// rewrite the whole look-ahead with newly mixed data
lastError = dsound.WriteToSoundBuffer(mix(), write)
if lastError != nil {
return
}
}
writeCursor = write
}
// Init sets up DirectSound and prepares for mixing and playing sounds. It
// starts a Go routine that periodically writes to the sound buffer to output
// to the sound card.
// Call Close when you are done with the mixer.
func Init() error {
initLock.Lock()
defer initLock.Unlock()
if inited {
return nil
}
if err := dsound.Init(44100); err != nil {
return err
}
writeAheadByteCount := bytesPerSecond / 10 // buffer 100ms
// make sure it is evenly dividable into samples
writeAheadByteCount -= writeAheadByteCount % bytesPerSample
writeAheadBuffer = make([]byte, writeAheadByteCount)
mixBuffer = make([]float32, writeAheadByteCount/2) // 2 bytes form one value
leftBuffer = mixBuffer[:len(mixBuffer)/2]
rightBuffer = mixBuffer[len(mixBuffer)/2:]
volume = 1
// initially write silence to sound buffer
if err := dsound.WriteToSoundBuffer(writeAheadBuffer, 0); err != nil {
return err
}
if err := dsound.StartSound(); err != nil {
return err
}
stop = make(chan bool)
go func() {
pulse := time.Tick(10 * time.Millisecond)
for {
select {
case <-pulse:
update()
if lastError != nil {
return
}
case <-stop:
return
default:
time.Sleep(1 * time.Millisecond)
}
}
}()
inited = true
return nil
}