audio: Add Volume/SetVolume

examples/audio/main.go

@@ -68,6 +68,7 @@ var (
 	seCh             = make(chan *wav.Stream)
 	mouseButtonState = map[ebiten.MouseButton]int{}
 	keyState         = map[ebiten.Key]int{}
+	volume128        = 128
 )
 
 func playerBarRect() (x, y, w, h int) {
@@ -105,6 +106,26 @@ func (p *Player) updateSE() error {
 	return sePlayer.Play()
 }
 
+func (p *Player) updateVolume() error {
+	if p.audioPlayer == nil {
+		return nil
+	}
+	if ebiten.IsKeyPressed(ebiten.KeyZ) {
+		volume128--
+	}
+	if ebiten.IsKeyPressed(ebiten.KeyX) {
+		volume128++
+	}
+	if volume128 < 0 {
+		volume128 = 0
+	}
+	if 128 < volume128 {
+		volume128 = 128
+	}
+	p.audioPlayer.SetVolume(float64(volume128) / 128)
+	return nil
+}
+
 func (p *Player) updatePlayPause() error {
 	if p.audioPlayer == nil {
 		return nil
@@ -171,6 +192,9 @@ func update(screen *ebiten.Image) error {
 		if err := musicPlayer.updateSE(); err != nil {
 			return err
 		}
+		if err := musicPlayer.updateVolume(); err != nil {
+			return err
+		}
 	}
 
 	op := &ebiten.DrawImageOptions{}
@@ -198,6 +222,7 @@ func update(screen *ebiten.Image) error {
 	msg := fmt.Sprintf(`FPS: %0.2f
 Press S to toggle Play/Pause
 Press P to play SE
+Press Z or X to change volume of the music
 %s`, ebiten.CurrentFPS(), currentTimeStr)
 	if musicPlayer == nil {
 		msg += "\nNow Loading..."

exp/audio/audio.go

@@ -153,6 +153,7 @@ type Player struct {
 	src     io.ReadSeeker
 	buf     []byte
 	pos     int64
+	volume  float64
 }
 
 // NewPlayer creates a new player with the given data to the given channel.
@@ -168,6 +169,7 @@ func (c *Context) NewPlayer(src io.ReadSeeker) (*Player, error) {
 		context: c,
 		src:     src,
 		buf:     []byte{},
+		volume:  1,
 	}
 	// Get the current position of the source.
 	pos, err := p.src.Seek(0, 1)
@@ -191,6 +193,7 @@ func (p *Player) bufferToInt16(lengthInBytes int) []int16 {
 	r := make([]int16, lengthInBytes/2)
 	for i := 0; i < lengthInBytes/2; i++ {
 		r[i] = int16(p.buf[2*i]) | (int16(p.buf[2*i+1]) << 8)
+		r[i] = int16(float64(r[i]) * p.volume)
 	}
 	return r
 }
@@ -245,5 +248,19 @@ func (p *Player) Current() time.Duration {
 	return time.Duration(p.pos/bytesPerSample/channelNum) * time.Second / time.Duration(p.context.sampleRate)
 }
 
-// TODO: Volume / SetVolume?
+func (p *Player) Volume() float64 {
+	return p.volume
+}
+
+func (p *Player) SetVolume(volume float64) {
+	// TODO: What if volume is NaN?
+	if 1 < volume {
+		panic("audio: volume must <= 1")
+	}
+	if volume < 0 {
+		panic("audio: volume must >= 0")
+	}
+	p.volume = volume
+}
+
 // TODO: Panning