audio: Add Context.IsReady

Fixes #717

audio/audio.go

@@ -170,6 +170,7 @@ type Context struct {
 	players    *players
 	sampleRate int
 	err        error
+	ready      bool
 
 	m sync.Mutex
 }
@@ -266,15 +267,27 @@ func (c *Context) loop() {
 		case <-suspendCh:
 			<-resumeCh
 		default:
-			const n = 2048
-			if _, err := io.CopyN(p, c.players, n); err != nil {
+			if _, err := io.CopyN(p, c.players, 2048); err != nil {
 				c.err = err
 				return
 			}
+			c.m.Lock()
+			c.ready = true
+			c.m.Unlock()
 		}
 	}
 }
 
+// IsReady returns a boolean value indicating whether the audio is ready or not.
+//
+// On some browsers, user interaction like click or pressing keys is required to start audio.
+func (c *Context) IsReady() bool {
+	c.m.Lock()
+	r := c.ready
+	c.m.Unlock()
+	return r
+}
+
 // Update is deprecated as of 1.6.0-alpha.
 //
 // As of 1.6.0-alpha, Update always returns nil and does nothing related to updating the state.

examples/pcm/main.go

@@ -139,7 +139,7 @@ var (
 
 func update(screen *ebiten.Image) error {
 	// Play notes for each half second.
-	if frames%30 == 0 {
+	if frames%30 == 0 && audioContext.IsReady() {
 		currentNote = playNote(scoreIndex)
 		scoreIndex++
 		scoreIndex %= len(score)
@@ -151,11 +151,14 @@ func update(screen *ebiten.Image) error {
 	}
 
 	msg := "Note: "
-	if currentNote == 'R' {
+	if currentNote == 'R' || currentNote == 0 {
 		msg += "-"
 	} else {
 		msg += string(currentNote)
 	}
+	if !audioContext.IsReady() {
+		msg += "\n\n(If the audio doesn't start,\n click the screen or press keys)"
+	}
 	ebitenutil.DebugPrint(screen, msg)
 	return nil
 }

go.mod

@@ -7,7 +7,7 @@ require (
 	github.com/gopherjs/gopherwasm v1.0.0
 	github.com/hajimehoshi/bitmapfont v1.1.1
 	github.com/hajimehoshi/go-mp3 v0.1.1
-	github.com/hajimehoshi/oto v0.2.0
+	github.com/hajimehoshi/oto v0.2.1-0.20181013145203-3a9bb05c78a0
 	github.com/jakecoffman/cp v0.1.0
 	github.com/jfreymuth/oggvorbis v1.0.0
 	github.com/jfreymuth/vorbis v1.0.0 // indirect

go.sum

@@ -24,6 +24,8 @@ github.com/hajimehoshi/oto v0.1.4 h1:YixDDnNhUjtrYP84YXISGWhQUN2VJfVIgKUeSNMWtxQ
 github.com/hajimehoshi/oto v0.1.4/go.mod h1:0ZepxT+2KLDrCm1gdkKBCQCxr+8fgQqoh0I7g+kr040=
 github.com/hajimehoshi/oto v0.2.0 h1:7JRO4/b+/xjWdV9ccUs35xcYTDrzRHxs5qnxeMHj7CM=
 github.com/hajimehoshi/oto v0.2.0/go.mod h1:0ZepxT+2KLDrCm1gdkKBCQCxr+8fgQqoh0I7g+kr040=
+github.com/hajimehoshi/oto v0.2.1-0.20181013145203-3a9bb05c78a0 h1:Ruf7x6Tkg6lx6fwHO8a38eR/cf+2GEX+9tAyJnqV8jc=
+github.com/hajimehoshi/oto v0.2.1-0.20181013145203-3a9bb05c78a0/go.mod h1:0ZepxT+2KLDrCm1gdkKBCQCxr+8fgQqoh0I7g+kr040=
 github.com/jakecoffman/cp v0.1.0 h1:sgSYEGUgfwiT447fRjloa2c5b6UyYP+7muR3gQK+Ep0=
 github.com/jakecoffman/cp v0.1.0/go.mod h1:a3xPx9N8RyFAACD644t2dj/nK4SuLg1v+jL61m2yVo4=
 github.com/jfreymuth/oggvorbis v1.0.0 h1:aOpiihGrFLXpsh2osOlEvTcg5/aluzGQeC7m3uYWOZ0=