audio: add Mixer

audio/mixer.go

@@ -0,0 +1,51 @@
+package audio
+
+type Mixer struct {
+	streamers []Streamer
+}
+
+func (m *Mixer) Play(s ...Streamer) {
+	m.streamers = append(m.streamers, s...)
+}
+
+func (m *Mixer) Stream(samples [][2]float64) (n int, ok bool) {
+	var tmp, mix [512][2]float64
+
+	for len(samples) > 0 {
+		toStream := len(mix)
+		if toStream > len(samples) {
+			toStream = len(samples)
+		}
+
+		// clear the mix buffer
+		for i := range mix[:toStream] {
+			mix[i] = [2]float64{}
+		}
+
+		for si := 0; si < len(m.streamers); si++ {
+			// mix the stream
+			sn, sok := m.streamers[si].Stream(tmp[:toStream])
+			for i := range tmp[:sn] {
+				mix[i][0] += tmp[i][0]
+				mix[i][1] += tmp[i][1]
+			}
+			if !sok {
+				// remove drained streamer
+				sj := len(m.streamers) - 1
+				m.streamers[si], m.streamers[sj] = m.streamers[sj], m.streamers[si]
+				m.streamers = m.streamers[:sj]
+				si--
+			}
+		}
+
+		// copy mix buffer into samples
+		for i := range mix[:toStream] {
+			samples[i] = mix[i]
+		}
+
+		samples = samples[toStream:]
+		n += toStream
+	}
+
+	return n, true
+}