Have the server tell the client whether there is a backing track, and…

… if so what kind, what's the client can use to decide whether to show the backing track volume slider, name it properly, and choose whether you can join the first packet. Fixes #169

html/demo.js

@@ -1118,7 +1118,7 @@ function update_active_users(
     if (userid == myUserid) {
       for (var j = 0 ; j < N_BUCKETS; j++) {
         window.buckets.children[j].children[0].children[1].disabled =
-          est_bucket === j;
+          (j == 0 && !backingTrackOn && !imLeading) || est_bucket === j;
       }
     }
 
@@ -1638,6 +1638,7 @@ function connect_twilio() {
   });
 }
 
+let backingTrackOn = false;
 async function start_singing() {
   var final_url = server_api_path();
 
@@ -1713,6 +1714,13 @@ async function start_singing() {
     if (metadata["backingVolume"] != null) {
       window.backingVolumeControl.value = metadata["backingVolume"];
     }
+    if (metadata["backing_track_type"] != null) {
+      const backingTrackType = metadata["backing_track_type"];
+      backingTrackOn = !!backingTrackType;
+      window.backingSliderDiv.style.display =
+        backingTrackOn ? "block" : "none";
+      window.backingTrackTypeName.innerText = backingTrackType;
+    }
 
     first_bucket_s = metadata["first_bucket"] || first_bucket_s;
 

html/index.html

@@ -197,7 +197,9 @@
     width: 12em;
   }
 }
-
+#backingSliderDiv {
+  display: none;
+}
 #remainderWindow {
   flex-grow: 1;
   display: flex;
@@ -1192,8 +1194,8 @@ <h3>Something else weird is going on</h3>
     <div id=spectatorMode>As a spectator, your singing is not included</div>
   </div>
 
-  <div>
-  <label for=backingVolumeSlider>Backing Volume:</label>
+  <div id=backingSliderDiv>
+  <label for=backingVolumeSlider><span id=backingTrackTypeName></span> Volume:</label>
   <input type="range" min="0" max="160" value="100" id="backingVolumeSlider">
   </div>
 

server.py

@@ -104,6 +104,7 @@ def reset(self):
 
         self.backing_track: Any = np.zeros(0)
         self.backing_track_index = 0
+        self.backing_track_type = ""
 
         self.max_position = DELAY_INTERVAL*LAYERING_DEPTH
 
@@ -469,6 +470,7 @@ def run_backing_track() -> None:
                 inf.readframes(-1), np.int16).astype(np.float32) / (2**15)
             state.backing_track *= 0.8 # turn it down a bit
             state.backing_track_index = 0
+            state.backing_track_type = "Backing Track"
 
     # Backing track is used only once.
     state.requested_track = None
@@ -766,6 +768,11 @@ def handle_json_post(in_json_raw, in_data):
         "x-audio-metadata": x_audio_metadata,
     }), out_data
 
+def end_song():
+    state.leader = None
+    state.backing_track_type = ""
+    sendall("backing_track_type", state.backing_track_type)
+
 # Handle special operations that do not require a user (although they may
 #   optionally support one), but can be done server-to-server as well.
 def handle_special(query_params, server_clock, user=None, client_read_clock=None):
@@ -817,16 +824,18 @@ def handle_special(query_params, server_clock, user=None, client_read_clock=None
             state.song_start_clock = server_clock
         state.song_end_clock = 0
 
+        state.backing_track_type = ""
         if state.bpm > 0:
             backfill_metronome()
+            state.backing_track_type = "Metronome"
         elif state.requested_track:
             run_backing_track()
             # These must be separate from song_start/end_clock, because they
             #   are used for video sync and must be EXACTLY at the moment the
             #   backing track starts/ends, not merely close.
             #insert_event("backingTrackStart", server_clock)
             #insert_event("backingTrackEnd", server_clock + len(state.backing_track))
-
+        sendall("backing_track_type", state.backing_track_type)
 
     if query_params.get("mark_stop_singing", None):
         # stop the backing track from playing, if it's still going
@@ -842,8 +851,7 @@ def handle_special(query_params, server_clock, user=None, client_read_clock=None
         else:
             state.song_end_clock = server_clock
 
-        state.leader = None
-
+        end_song()
 
     if query_params.get("clear_events", None):
         events.clear()
@@ -977,7 +985,7 @@ def handle_post(in_json, in_data) -> Tuple[Any, str]:
         if state.backing_track_index == len(state.backing_track):
             # the song has ended, mark it so
             state.song_end_clock = clear_index
-            state.leader = None
+            end_song()
 
     if clear_samples > 0:
         if state.bpm > 0: