Add .Playing() function to Track interface

interface.go

@@ -36,6 +36,7 @@ type Engine interface {
 // Playable is a music or sound effect object that can be played and managed.
 type Playable interface {
 	Play(loops int) error
+	Playing() bool
 	Pause() error
 	Stop() error
 

sdl/currently_playing.go

@@ -0,0 +1,30 @@
+package sdl
+
+import "errors"
+
+// setPlaying associates a channel no. to the Track playing.
+func (e *Engine) setPlaying(channel int, t *Track) {
+	e.channelMu.Lock()
+	defer e.channelMu.Unlock()
+	e.channelsPlaying[channel] = t
+}
+
+// unsetPlaying associates a channel no. to the Track playing.
+func (e *Engine) unsetPlaying(channel int) error {
+	e.channelMu.Lock()
+	defer e.channelMu.Unlock()
+	if track, ok := e.channelsPlaying[channel]; ok {
+		track.channel = -1
+		delete(e.channelsPlaying, channel)
+		return nil
+	}
+	return errors.New("didn't even know channel %d was playing a sound")
+}
+
+// isPlaying checks if a sound effect is playing on a channel.
+func (e *Engine) isPlaying(channel int) bool {
+	e.channelMu.RLock()
+	defer e.channelMu.RUnlock()
+	_, ok := e.channelsPlaying[channel]
+	return ok
+}

sdl/music.go

@@ -9,6 +9,8 @@ import (
 type Track struct {
 	isMusic bool // false = is sound effect
 
+	engine *Engine
+
 	// If isMusic
 	mus *mix.Music
 
@@ -46,6 +48,7 @@ func (e *Engine) LoadSound(filename string) (Track, error) {
 	wav, err := mix.LoadWAV(filename)
 	return Track{
 		isMusic: false,
+		engine:  e,
 		wav:     wav,
 		channel: -1,
 	}, err
@@ -62,6 +65,7 @@ func (e *Engine) LoadSoundBin(data []byte) (Track, error) {
 	wav, err := mix.LoadWAVRW(rw, false)
 	return Track{
 		isMusic: false,
+		engine:  e,
 		wav:     wav,
 		channel: -1,
 	}, err
@@ -93,9 +97,18 @@ func (t *Track) Play(loops int) error {
 	}
 	channel, err := t.wav.Play(-1, loops)
 	t.channel = channel
+	t.engine.setPlaying(channel, t)
 	return err
 }
 
+// Playing tells if this sound is already playing.
+func (t *Track) Playing() bool {
+	if t.isMusic {
+		return mix.PlayingMusic()
+	}
+	return t.channel >= 0 && t.engine.isPlaying(t.channel)
+}
+
 // Pause the track.
 func (t Track) Pause() error {
 	if t.isMusic {

sdl/sdl.go

@@ -1,24 +1,35 @@
 // Package sdl implements an audio engine using libSDL2.
 package sdl
 
-import "github.com/veandco/go-sdl2/mix"
+import (
+	"sync"
+
+	"github.com/veandco/go-sdl2/mix"
+)
 
 // Engine is the SDL2 audio engine.
 type Engine struct {
 	initFlags int
+
+	// Keep track of which SDL channel numbers are ACTUALLY playing sound
+	// effects right now, and watch for when the channels are finished.
+	channelMu       sync.RWMutex
+	channelsPlaying map[int]*Track
 }
 
 // New initializes an SDL2 Mixer for the audio engine.
 //
 // Pass the SDL2 Mixer flags for its initialization. The flags are an OR'd
 // value made up of:
-//    mix.INIT_MP3
-//    mix.INIT_OGG
-//    mix.INIT_FLAC
-//    mix.INIT_MOD
+//
+//	mix.INIT_MP3
+//	mix.INIT_OGG
+//	mix.INIT_FLAC
+//	mix.INIT_MOD
 func New(flags int) (*Engine, error) {
 	return &Engine{
-		initFlags: flags,
+		initFlags:       flags,
+		channelsPlaying: map[int]*Track{},
 	}, nil
 }
 
@@ -29,6 +40,11 @@ func (e *Engine) Setup() error {
 		return err
 	}
 
+	// Subscribe to sound effect channels finishing.
+	mix.ChannelFinished(func(channel int) {
+		_ = e.unsetPlaying(channel)
+	})
+
 	// Open the audio mixer.
 	// the '2' is stereo (two channels), '1' would be mono.
 	// 4096 is the chunk size.