refactor: AudioSource is a func instead of single function interface

This avoids defining Processor altogether.

audio.go

@@ -29,11 +29,9 @@ type (
 		Play(r AudioSource) CloserWaiter
 	}
 
-	// AudioSource is an interface for reading audio samples into an
-	// AudioBuffer. Returns error if the buffer is not filled.
-	AudioSource interface {
-		ReadAudio(buf AudioBuffer) error
-	}
+	// AudioSource is an function for reading audio samples into an AudioBuffer.
+	// Returns error if the buffer is not filled.
+	AudioSource func(buf AudioBuffer) error
 
 	BufferSource struct {
 		buffer AudioBuffer
@@ -154,8 +152,15 @@ func (buffer AudioBuffer) Fill(synth Synth) error {
 	return nil
 }
 
-func (b AudioBuffer) Source() *BufferSource {
-	return &BufferSource{buffer: b}
+func (b AudioBuffer) Source() AudioSource {
+	return func(buf AudioBuffer) error {
+		n := copy(buf, b)
+		b = b[n:]
+		if n < len(buf) {
+			return io.EOF
+		}
+		return nil
+	}
 }
 
 // ReadAudio reads audio samples from an AudioSource into an AudioBuffer.

cmd/sointu-track/main.go

@@ -10,6 +10,7 @@ import (
 	"runtime/pprof"
 
 	"gioui.org/app"
+	"github.com/vsariola/sointu"
 	"github.com/vsariola/sointu/cmd"
 	"github.com/vsariola/sointu/oto"
 	"github.com/vsariola/sointu/tracker"
@@ -61,8 +62,10 @@ func main() {
 	}
 
 	trackerUi := gioui.NewTracker(model)
-	processor := tracker.NewProcessor(player, midiContext, trackerUi)
-	audioCloser := audioContext.Play(processor)
+	audioCloser := audioContext.Play(func(buf sointu.AudioBuffer) error {
+		player.Process(buf, midiContext, trackerUi)
+		return nil
+	})
 
 	go func() {
 		trackerUi.Main()

oto/oto.go

@@ -77,7 +77,7 @@ func (o *OtoReader) Read(b []byte) (n int, err error) {
 	} else if samples < len(o.tmpBuffer) {
 		o.tmpBuffer = o.tmpBuffer[:samples]
 	}
-	err = o.audioSource.ReadAudio(o.tmpBuffer)
+	err = o.audioSource(o.tmpBuffer)
 	if err != nil {
 		return o.closeWithError(err)
 	}

tracker/processor.go

@@ -1,20 +0,0 @@
-package tracker
-
-import (
-	"github.com/vsariola/sointu"
-)
-
-type Processor struct {
-	*Player
-	playerProcessContext PlayerProcessContext
-	uiProcessor          EventProcessor
-}
-
-func NewProcessor(player *Player, context PlayerProcessContext, uiProcessor EventProcessor) *Processor {
-	return &Processor{player, context, uiProcessor}
-}
-
-func (p *Processor) ReadAudio(buf sointu.AudioBuffer) error {
-	p.Player.Process(buf, p.playerProcessContext, p.uiProcessor)
-	return nil
-}