audio: optimize Mixer.Stream and Mix(...).Stream (remove unnecessary mix buffer)

audio/compositors.go

@@ -42,17 +42,17 @@ func Seq(s ...Streamer) Streamer {
 // Mix takes zero or more Streamers and returns a Streamer which streames them mixed together.
 func Mix(s ...Streamer) Streamer {
 	return StreamerFunc(func(samples [][2]float64) (n int, ok bool) {
-		var tmp, mix [512][2]float64
+		var tmp [512][2]float64
 
 		for len(samples) > 0 {
-			toStream := len(mix)
+			toStream := len(tmp)
 			if toStream > len(samples) {
 				toStream = len(samples)
 			}
 
-			// clear the mix buffer
-			for i := range mix[:toStream] {
-				mix[i] = [2]float64{}
+			// clear the samples
+			for i := range samples[:toStream] {
+				samples[i] = [2]float64{}
 			}
 
 			snMax := 0 // max number of streamed samples in this iteration
@@ -65,18 +65,13 @@ func Mix(s ...Streamer) Streamer {
 				ok = ok || sok
 
 				for i := range tmp[:sn] {
-					mix[i][0] += tmp[i][0]
-					mix[i][1] += tmp[i][1]
+					samples[i][0] += tmp[i][0]
+					samples[i][1] += tmp[i][1]
 				}
 			}
 
-			// copy mix buffer into samples
-			for i := range mix[:snMax] {
-				samples[i] = mix[i]
-			}
-
 			n += snMax
-			if snMax < len(mix) {
+			if snMax < len(tmp) {
 				break
 			}
 			samples = samples[snMax:]

audio/mixer.go

@@ -13,25 +13,25 @@ func (m *Mixer) Play(s ...Streamer) {
 }
 
 func (m *Mixer) Stream(samples [][2]float64) (n int, ok bool) {
-	var tmp, mix [512][2]float64
+	var tmp [512][2]float64
 
 	for len(samples) > 0 {
-		toStream := len(mix)
+		toStream := len(tmp)
 		if toStream > len(samples) {
 			toStream = len(samples)
 		}
 
-		// clear the mix buffer
-		for i := range mix[:toStream] {
-			mix[i] = [2]float64{}
+		// clear the samples
+		for i := range samples[:toStream] {
+			samples[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]
+				samples[i][0] += tmp[i][0]
+				samples[i][1] += tmp[i][1]
 			}
 			if !sok {
 				// remove drained streamer
@@ -42,11 +42,6 @@ func (m *Mixer) Stream(samples [][2]float64) (n int, ok bool) {
 			}
 		}
 
-		// copy mix buffer into samples
-		for i := range mix[:toStream] {
-			samples[i] = mix[i]
-		}
-
 		samples = samples[toStream:]
 		n += toStream
 	}