Playlist: add method SongStarted()

Empty currently, but code will be added song.

src/queue/Playlist.cxx

@@ -60,6 +60,12 @@ playlist::QueueSongOrder(PlayerControl &pc, unsigned order)
 	pc.EnqueueSong(new DetachedSong(song));
 }
 
+void
+playlist::SongStarted()
+{
+	assert(current >= 0);
+}
+
 inline void
 playlist::QueuedSongStarted(PlayerControl &pc)
 {
@@ -78,6 +84,8 @@ playlist::QueuedSongStarted(PlayerControl &pc)
 		DeleteOrder(pc, old_current);
 
 	idle_add(IDLE_PLAYER);
+
+	SongStarted();
 }
 
 const DetachedSong *
@@ -152,6 +160,8 @@ playlist::PlayOrder(PlayerControl &pc, int order)
 
 	pc.Play(new DetachedSong(song));
 	current = order;
+
+	SongStarted();
 }
 
 void

src/queue/Playlist.hxx

@@ -134,6 +134,17 @@ protected:
 	 */
 	void OnModified();
 
+	/**
+	 * Called when playback of a new song starts.  Unlike
+	 * QueuedSongStarted(), this also gets called when the user
+	 * manually switches to another song.  It may be used for
+	 * playlist fixups.
+	 *
+	 * The song being started is specified by the #current
+	 * attribute.
+	 */
+	void SongStarted();
+
 	/**
 	 * Updates the "queued song".  Calculates the next song
 	 * according to the current one (if MPD isn't playing, it
@@ -152,7 +163,8 @@ protected:
 
 	/**
 	 * Called when the player thread has started playing the
-	 * "queued" song.
+	 * "queued" song, i.e. it has switched from one song to the
+	 * next automatically.
 	 */
 	void QueuedSongStarted(PlayerControl &pc);