The piano now has an internal ADSR

examples/piano/main.go

@@ -1,6 +1,7 @@
 package main
 
 import "math"
+import "time"
 import "errors"
 import "github.com/faiface/beep"
 import "github.com/faiface/beep/speaker"
@@ -15,7 +16,7 @@ const sampleRate = 44100
 const bufferSize = 256
 var   tuning     = music.EqualTemparment { A4: 440 }
 var   waveform   = 0
-var playing = map[music.Note] *beep.Ctrl { }
+var playing = map[music.Note] *toneStreamer { }
 
 func main () {
 	speaker.Init(sampleRate, bufferSize)
@@ -59,17 +60,27 @@ func stopNote (note music.Note) {
 	if _, is := playing[note]; !is { return }
 	
 	speaker.Lock() 
-	playing[note].Streamer = nil
+	playing[note].Release()
 	delete(playing, note)
 	speaker.Unlock()
 }
 
 func playNote (note music.Note) {
-	streamer, _ := Tone(sampleRate, int(tuning.Tune(note)), waveform, 0.3)
+	streamer, _ := Tone (
+		sampleRate,
+		int(tuning.Tune(note)),
+		waveform,
+		0.3,
+		ADSR {
+			Attack:  100 * time.Millisecond,
+			Decay:   400 * time.Millisecond,
+			Sustain: 0.7,
+			Release: 500 * time.Millisecond,
+		})
 
 	stopNote(note)
 	speaker.Lock()
-	playing[note] = &beep.Ctrl { Streamer: streamer }
+	playing[note] = streamer
 	speaker.Unlock()
 	speaker.Play(playing[note])
 }
@@ -80,30 +91,62 @@ func playNote (note music.Note) {
 type toneStreamer struct {
 	position float64
 	delta    float64
+	
 	waveform int
 	gain     float64
+
+	adsr     ADSR
+	released bool
+	complete bool
+
+	adsrPhase    int
+	adsrPosition float64
+	adsrDeltas   [4]float64
+}
+
+type ADSR struct {
+	Attack  time.Duration
+	Decay   time.Duration
+	Sustain float64
+	Release time.Duration
 }
 
 func Tone (
-	sr beep.SampleRate,
-	freq int,
+	sampleRate beep.SampleRate,
+	frequency int,
 	waveform int,
 	gain float64,
+	adsr ADSR,
 ) (
-	beep.Streamer,
+	*toneStreamer,
 	error,
 ) {
-	if int(sr) / freq < 2 {
+	if int(sampleRate) / frequency < 2 {
 		return nil, errors.New (
 			"tone generator: samplerate must be at least " +
 			"2 times greater then frequency")
 	}
+	
 	tone := new(toneStreamer)
-	tone.position = 0.0
 	tone.waveform = waveform
-	steps := float64(sr) / float64(freq)
+	tone.position = 0.0
+	steps := float64(sampleRate) / float64(frequency)
 	tone.delta = 1.0 / steps
 	tone.gain = gain
+
+	if adsr.Attack  < time.Millisecond { adsr.Attack  = time.Millisecond }
+	if adsr.Decay   < time.Millisecond { adsr.Decay   = time.Millisecond }
+	if adsr.Release < time.Millisecond { adsr.Release = time.Millisecond }
+	tone.adsr = adsr
+
+	attackSteps  := adsr.Attack.Seconds()  * float64(sampleRate)
+	decaySteps   := adsr.Decay.Seconds()   * float64(sampleRate)
+	releaseSteps := adsr.Release.Seconds() * float64(sampleRate)
+	tone.adsrDeltas[0] = 1 / attackSteps
+	tone.adsrDeltas[1] = 1 / decaySteps
+	tone.adsrDeltas[2] = 0
+	tone.adsrDeltas[3] = 1 / releaseSteps
+	
 	return tone, nil
 }
 
@@ -127,17 +170,59 @@ func (tone *toneStreamer) nextSample () (sample float64) {
 			28.32 * tone.position * tone.position +
 			15.62 * tone.position * tone.position * tone.position
 	}
+
+	adsrGain := 0.0
+	switch tone.adsrPhase {
+	case 0: adsrGain = tone.adsrPosition
+		if tone.adsrPosition > 1 {
+			tone.adsrPosition = 0
+			tone.adsrPhase = 1
+		}
+		
+	case 1: adsrGain = 1 + tone.adsrPosition * (tone.adsr.Sustain - 1)
+		if tone.adsrPosition > 1 {
+			tone.adsrPosition = 0
+			tone.adsrPhase = 2
+		}
+		
+	case 2: adsrGain = tone.adsr.Sustain
+		if tone.released {
+			tone.adsrPhase = 3
+		}
+		
+	case 3: adsrGain = (1 - tone.adsrPosition) * tone.adsr.Sustain
+		if tone.adsrPosition > 1 {
+			tone.adsrPosition = 0
+			tone.complete = true
+		}
+	}
+
+	sample *= adsrGain * adsrGain
+	
+	tone.adsrPosition += tone.adsrDeltas[tone.adsrPhase]
 	_, tone.position = math.Modf(tone.position + tone.delta)
 	return
 }
 
 func (tone *toneStreamer) Stream (buf [][2]float64) (int, bool) {
+	if tone.complete {
+		return 0, false
+	}
+
 	for i := 0; i < len(buf); i++ {
-		sample := tone.nextSample() * tone.gain
+		sample := 0.0
+		if !tone.complete {
+			sample = tone.nextSample() * tone.gain
+		}
 		buf[i] = [2]float64{sample, sample}
 	}
 	return len(buf), true
 }
+
 func (tone *toneStreamer) Err () error {
 	return nil
 }
+
+func (tone *toneStreamer) Release () {
+	tone.released = true
+}