[update] Added debug-music-offset-beat command-line option.

src/main.d

@@ -36,11 +36,16 @@ 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
+      "debug-music-offset-beat", &args.debug_music_offset_beat,
+      "debug-music-index",       &args.debug_music_index,
+      "window-size",             &args.window_size
     );
 
   auto valid = true;
+  if (args.debug_music_offset_beat < 0) {
+    "invalid music offset (it should be 0 or more)".writeln;
+    valid = false;
+  }
   if (args.window_size <= 100) {
     "invalid window size (it should be 100 or more)".writeln;
     valid = false;

src/sj/Args.d

@@ -9,4 +9,6 @@ struct Args {
 
   ///
   int debug_music_index = -1;
+  ///
+  float debug_music_offset_beat = 0;
 }

src/sj/LoadingScene.d

@@ -35,17 +35,18 @@ class LoadingScene : SceneInterface {
   }
 
   ///
-  void Initialize(Music music) {
-    music_ = music;
+  void Initialize(Music music, float offset_beat = 0) {
+    music_       = music;
+    offset_beat_ = offset_beat;
 
     first_drawn_ = false;
   }
   override SceneInterface Update(KeyInput input) {
     if (first_drawn_) {
-      // TODO: parallelize contex creation
+      // TODO: parallelize context creation
       auto context = music_.CreatePlayerContext(
           vec2i(args_.window_size, args_.window_size), programs_.player);
-      play_scene_.Initialize(music_, context);
+      play_scene_.Initialize(music_, context, offset_beat_);
       return play_scene_;
     }
     return this;
@@ -67,6 +68,7 @@ class LoadingScene : SceneInterface {
   LobbyWorld lobby_;
 
   Music music_;
+  float offset_beat_;
 
   bool first_drawn_;
 }

src/sj/Music.d

@@ -64,8 +64,9 @@ class Music {
   }
 
   ///
-  void PlayForGame() {
-    sfMusic_setPlayingOffset(music_, sfMilliseconds(0));
+  void PlayForGame(float offset_beat) {
+    sfMusic_setPlayingOffset(music_,
+        sfMilliseconds((offset_beat*bpm_ / 60f / 1e-6f).to!int));
     sfMusic_play(music_);
   }
   ///

src/sj/PlayScene.d

@@ -35,13 +35,13 @@ class PlayScene : SceneInterface {
   }
 
   ///
-  void Initialize(Music music, sjplayer.Context context) {
+  void Initialize(Music music, sjplayer.Context context, float offset_beat = 0) {
     music_   = music;
     context_ = context;
 
     score_ = BaseScore;
 
-    music_.PlayForGame();
+    music_.PlayForGame(offset_beat);
   }
   override SceneInterface Update(KeyInput input) {
     beat_ = music_.beat;