[update] Added a debug-music-index command-line option.

src/main.d

@@ -36,6 +36,7 @@ int main(string[] unparsed_args) {
 
 private bool ParseArgs(string[] unparsed_args, out Args args) {
   auto helpinfo = unparsed_args.getopt(
+      "debug-music-index", &args.debug_music_index,
       "window-size",       &args.window_size
     );
 

src/sj/Args.d

@@ -6,4 +6,7 @@ struct Args {
  public:
   ///
   int window_size = 600;
+
+  ///
+  int debug_music_index = -1;
 }

src/sj/Game.d

@@ -2,6 +2,7 @@
 module sj.Game;
 
 import std.algorithm,
+       std.exception,
        std.file,
        std.json,
        std.path;
@@ -48,9 +49,16 @@ class Game : AbstractGame {
     play_  .SetupSceneDependency(result_);
     result_.SetupSceneDependency(title_);
 
+    if (args.debug_music_index >= 0) {
+      enforce(args.debug_music_index < music_list.length);
+      load_.Initialize(music_list_[args.debug_music_index]);
+      super(load_);
+
+    } else {
       title_.Initialize();
       super(title_);
     }
+  }
 
   ~this() {
     title_.destroy();