Added volume controls

pkg/track_player.go

@@ -2,24 +2,43 @@ package gomus
 
 import (
 	"github.com/faiface/beep"
+	"github.com/faiface/beep/effects"
 	"github.com/faiface/beep/speaker"
 )
 
+const (
+	base        = 2
+	minVolume   = -5
+	maxVolume   = 1
+	startVolume = -2
+)
+
+type TrackPlayerEffects struct {
+	volume float64
+}
+
+func newTrackPlayerEffects() TrackPlayerEffects {
+	return TrackPlayerEffects{volume: startVolume}
+}
+
 type TrackPlayer struct {
 	streamer   *beep.StreamSeekCloser
 	playerCtrl *beep.Ctrl
+	playerVol  *effects.Volume
 }
 
-func (t *TrackPlayer) Play(streamer *beep.StreamSeekCloser) {
+func (t *TrackPlayer) Play(streamer *beep.StreamSeekCloser, trackEffects *TrackPlayerEffects) {
 	if t.streamer != nil {
 		t.Close()
 	}
 
 	ctrl := &beep.Ctrl{Streamer: beep.Loop(-1, *streamer), Paused: false}
-	speaker.Play(ctrl)
+	volume := &effects.Volume{Streamer: ctrl, Base: base, Volume: trackEffects.volume, Silent: false}
+	speaker.Play(volume)
 
-	t.playerCtrl = ctrl
 	t.streamer = streamer
+	t.playerCtrl = ctrl
+	t.playerVol = volume
 }
 
 func (t *TrackPlayer) TogglePause() bool {
@@ -30,6 +49,12 @@ func (t *TrackPlayer) TogglePause() bool {
 	return newState
 }
 
+func (t *TrackPlayer) SetVolume(volume float64) {
+	speaker.Lock()
+	(*t.playerVol).Volume = volume
+	speaker.Unlock()
+}
+
 func (t *TrackPlayer) Close() {
 	(*t.streamer).Close()
 }