rough implementation for changing background music

script/audio.js

@@ -4,26 +4,81 @@
 var AudioEngine = {
     AUDIO_BUFFER_CACHE: {},
     audioContext: null,
-    output: null,
+    master: null,
+
+    // Tracks for playing music and sound effects
+    // 0 - Background music
+    // 1 - Background music
+    // 2 - Sound effects
+    // 3 - Sound effects
+    tracks: null,
+    currentBackgroundChannel: 0,
+    currentTrack: null,
 	init: function(options) {
         // for legacy browsers
         this.audioContext = new (window.AudioContext || window.webkitAudioContext);
-        this.output = this.audioContext.createGain();
-        this.output.connect(this.audioContext.destination);
+
+        // create master
+        this.master = this.audioContext.createGain();
+        this.master.connect(this.audioContext.destination);
+
+        // create 4 tracks to output to master
+        this.tracks = [];
+        for (var i = 0; i < 4; i++) {
+            this.tracks[i] = this.audioContext.createGain();
+            this.tracks[i].connect(this.master);
+        }
 	},
 	options: {}, // Nothing for now
-    _playAudioBuffer: function(buffer, loop) {
+    _playSound: function(buffer) {
         var source = this.audioContext.createBufferSource();
         source.buffer = buffer;
-        source.connect(this.output);
-        source.loop = loop || false;
+        source.connect(this.tracks[1]);
         source.start(0);
     },
-	playSound: function(src, loop) {
+    _fadeTrack: function(buffer) {
+        var newTrack = this.audioContext.createBufferSource();
+        newTrack.buffer = buffer;
+        newTrack.loop = true;
+
+        // figure out which background track to start on
+        // in order to do crossfade
+        var nextBackgroundChannel;
+        if (this.currentBackgroundChannel === 0) {
+            nextBackgroundChannel = 1;
+        } else {
+            nextBackgroundChannel = 0;
+        }
+        
+        // fade in new track
+        var fadeTime = this.audioContext.currentTime + 5.0;
+        newTrack.connect(this.tracks[nextBackgroundChannel]);
+        newTrack.start(0);
+        this.tracks[nextBackgroundChannel].gain.setValueAtTime(0.0, this.audioContext.currentTime);
+        this.tracks[nextBackgroundChannel].gain.linearRampToValueAtTime(1.0, fadeTime);
+
+        // fade out old track
+        this.tracks[this.currentBackgroundChannel].gain.linearRampToValueAtTime(0.0, fadeTime);
+        if (this.currentTrack) {
+            this.currentTrack.stop(fadeTime + 1.0); // make sure fade has completed
+        }
+
+        // switch background track
+        this.currentBackgroundChannel = nextBackgroundChannel;
+        this.currentTrack = newTrack;
+    },
+	changeMusic: function(src) {
         var self = this;
         this.loadAudioFile(src)
             .then(function (buffer) {
-                self._playAudioBuffer(buffer, loop);
+                self._fadeTrack(buffer);
+            });
+    },
+	playSound: function(src) {
+        var self = this;
+        this.loadAudioFile(src)
+            .then(function (buffer) {
+                self._playSound(buffer);
             });
     },
     loadAudioFile(src) {

script/engine.js

@@ -597,7 +597,7 @@
 				Engine.activeModule = module;
 				module.onArrival(diff);
 				Notifications.printQueue(module);
-
+				AudioEngine.changeMusic(module.music);
 			}
 		},
 

script/outside.js

@@ -3,6 +3,7 @@
  */
 var Outside = {
 	name: _("Outside"),
+	music: '/audio/outside.wav',
 	
 	_STORES_OFFSET: 0,
 	_GATHER_DELAY: 60,

script/room.js

@@ -10,7 +10,7 @@ var Room = {
 	_NEED_WOOD_DELAY: 15 * 1000, // from when the stranger shows up, to when you need wood
 	
 	buttons:{},
-	
+	music: '/audio/room.wav',
 	Craftables: {
 		'trap': {
 			name: _('trap'),